Dissertations / Theses on the topic 'Resonance searches'
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Lenz, Tatjana [Verfasser]. "Prospects for ttbar resonance searches at ATLAS / Tatjana Lenz." Wuppertal : Universitätsbibliothek Wuppertal, 2011. http://d-nb.info/1011113201/34.
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Ferapontov, Alexey V. "Measurements and searches for new physics in diboson processes with the D0 detector." Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1347.
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Schliephake, Thorsten [Verfasser]. "Resonance Searches with the tt Invariant Mass Distribution measured with the DØ Experiment at √s = 1.96 TeV / Thorsten Schliephake." Wuppertal : Universitätsbibliothek Wuppertal, 2010. http://d-nb.info/1006178279/34.
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Antel, Claire [Verfasser], and Monica [Akademischer Betreuer] Dunford. "Enhancing low mass dark matter mediator resonance searches with improved triggering in the ATLAS detector / Claire Antel ; Betreuer: Monica Dunford." Heidelberg : Universitätsbibliothek Heidelberg, 2019. http://d-nb.info/1180394445/34.
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Beresford, Lydia Audrey. "Searches for dijet resonances using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:c516b04b-2763-487a-a633-6c506cec93ad.
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This thesis presents three searches for new resonances in dijet invariant mass spectra. The spectra are produced using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector. New dijet resonances are searched for in the mass range 200 GeV to 6.9 TeV in mass. Heavy new resonances, with masses above 1.1 TeV, are targeted by a high mass dijet search. Light new resonances, with masses down to 200 GeV, are searched for in dijet events with an associated high momentum object (a photon or a jet) arising from initial state radiation. The associated object is used to efficiently trigger the recording of low mass dijet events. All of the analyses presented in this thesis search for an excess of events, localised in mass, above a data-derived estimate of the smoothly falling QCD background. In each search no evidence for new resonances is observed, and the data are used to set 95% C.L. limits on the production cross-section times acceptance times branching ratio for model-independent Gaussian resonance shapes, as well as benchmark signals. One particular benchmark signal which is considered in all of the searches is an axial-vector Z' dark matter mediator model whose parameter space is reduced due to the results presented in this thesis.
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Kunigo, Takuto. "Diboson resonance searches in the final state of the ℓvqq with improved large-R jet uncertainties in pp collisions at √s = 13 TeV with the ATLAS detector." Kyoto University, 2019. http://hdl.handle.net/2433/242598.
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Chung, Soo J. "Search for composite signatures at the Z Ìresonance." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/33520.
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Necula, Valentin. "Search for heavy resonances decaying into tt pairs." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0015671.
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Romano, Saez Silvestre Marino. "Search for ttbar resonances using the ATLAS detector." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22736/document.
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Le Modèle Standard (MS) de la physique des particules décrit les particules élémentaires et leurs interactions à l'exception de la gravité. Jusqu'à présent, la plupart des résultats expérimentaux sont en accord avec les prédictions du MS. Cependant, il existe encore des questions de nature expérimentale ou théorique qui restent sans réponse. Les particules massives qui se désintègrent en une paire de quarks top-antitop sont prédites par certains des modèles de physique au-delà du Modèle Standard, qui tentent de répondre à ces questions.Une recherche de nouvelles résonances tt est présentée dans ce manuscrit, en utilisant l'ensemble de données 2015 (début des Run 2) à partir des collisions proton-proton produites par le Large Hadron Collider (LHC) avec une énergie de faisceau de 13 TeV dans le centre de masse et avec une luminosité intégrée de 3.2 fb-1 recueillie par le détecteur ATLAS. La signature de l'état final recherché est caractérisée par la présence d'un électron ou d'un muon, d'un certain nombre de jets de hadrons et de l'énergie transverse manquante. La masse invariante des systèmes tt (mrecott ) est la principale observable sur cette recherche, et est utilisée pour tester la compatibilité des données avec l'hypothèse MS seule. Pour la région à grand mtt, les quarks top sont produits avec un grande impulsion et leurs produits de désintégration sont collimatés. Dans cette région, la sous-structure des jets doit être utilisée pour identifier les paires tt (scénario « boosted »), tandis que pour de basses valeurs de mtt, les produits de désintégration des quark top sont bien séparés (scénario « resolved »).Les résultats préliminaires sur l'analyse « boosted » sont présentés dans ce manuscrit. Dans les spectres de masse analysés, aucune preuve de l'existence de nouvelles particules n'a été trouvée. Pour une boson Z’TC2 « Topcolor assisted technicolor » avec une largeur relative de 1.2 %, des masses inférieures à 2 TeV sont exclues, l'améliorant les limites antérieures obtenues lors du Run 1. Des études de perspective pour inclure les topologies « resolved » sont également discutées, avec en particulier l'estimation du bruit de fond multi-jet en utilisant la « méthode de la matrice ». En outre, la méthode d'étalonnage des jets in-situ est proposée pour améliorer la résolution sur mtt. L'impact après chaque étape de la procédure de mise à l'échelle est présentée en utilisant des simulations à 8 TeVMassive particles decaying into a top-antitop pair (tt) are predicted by many theoretical models, which are introduced to provide explanations to the various open questions raised by the current formulation of the Standard Model of Particle Physics (SM). A search for new tt resonances is presented in this manuscript, using the 2015 dataset (early Run 2) from the proton-proton collisions at Large Hadron Collider (LHC) with a beam energy of 13 TeV at the centre-of-mass and with an integrated luminosity of 3.2 fb-1 collected by the ATLAS detector. The final state signature focuses on the lepton-plus-jets channel, which is characterised by the presence of an electron or muon, certain number of jets of hadrons and missing transverse energy. The invariant mass of the tt system (mtt) is the main observable on this search, which is used to test the compatibility of the data with the SM-only hypothesis. For the high mtt region, the selected events are dominated by top-quarks with collimated decay products, and jet substructure techniques have to be used to select the tt pairs (boosted scenario), while for low mtt, the selected events are dominated by top-quarks with well separated decay products (resolved scenario).Preliminary results on the boosted analysis are presented in this manuscript. In the analysed mass spectra, no evidence of the existence of new particles was found. For a topcolor-assisted technicolorZ’TC2 boson with a relative width of 1.2%, masses below 2 TeV are excluded, improving the previous limits obtained at Run 1. Perspective studies to include the resolved topologies are also discussed, where the estimation of the QCD multi-jet background using the « matrix method » is exposed in detail. In addition, the in-situ « jet rescaling » method is proposed to improve the mtt resolution. The impact after each step of the rescaling procedure is presented using 8 TeV simulations
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Yoon, Choong-Jae. "Search for Η-dibaryon resonance in 12C(K[-], K[+]ΛΛX) reaction." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136832.
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Williams, Catherine F. M. "Diffusion-weighted magnetic resonance imaging techniques." Thesis, University of Aberdeen, 1998. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602003.
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The aim of this project was to compare and evaluate other, non-EPI, diffusion-weighted MRI (DWI) sequences, through imaging experiments, on a phantom and in vivo, (using a 0.95 T system) and computer simulations, and to develop improved DWI methodology which could be implemented on standard hardware. Pulsed gradient spin echo (PGSE) and diffusion-weighted STEAM are slow multiple shot sequences, with measurement times of several minutes. Both sequences are highly sensitive to patient motion, but motion artifact was virtually eliminated using navigator echo phase correction and EGG triggering when diffusion-sensitisation was in the phase-encoding direction. It was demonstrated that both sequences can provide high quality images and allow accurate and straightforward diffusion-coefficient measurement when an imaging time period in the region of 20-30 minutes is available and when diffusion-sensitisation is required in one or two directions. A third direction of diffusion-sensitisation may be feasible if more sophisticated immobilisation or phase correction techniques are employed. A choice between PGSE or STEAM for a given application should take account of the Ti and T2 values of the imaged tissues, since a higher SNR might be provided by STEAM when the T1T2 ratio is high. A diffusion-weighted CE-FAST sequence was implemented with the novel modification of acquisition of a navigator gradient-echo, which was shown to reduce motion artifact when diffusion-sensitisation was in the phase-encoding direction. However, it has been demonstrated by other workers that unknown signal losses due to motion-induced phase incoherence between signal components may remain. The SNR (normalised with respect to the square root of the imaging time) in the phantom and in white matter was similar to that obtained using PGSE, but an advantage of CE- FAST is that it can be performed in a fraction of the measurement time of PGSE. Diffusion-sensitivity was much higher than in other sequences and the diffusion- attenuation was found to agree with an analysis presented in the literature. However, a major disadvantage of the technique, which precludes its use for many DWI applications, is the requirement of accurate knowledge of Ti, T2 and flip angle in order to calculate the diffusion coefficient or tensor. Prior to a study of diffusion-weighted snapshot FLASH, the effects of magnetisation evolution during snapshot FLASH acquisition on image quality and parameter measurement accuracy were first investigated, through phantom experiments and computer simulations, in the context of a r2-weighted snapshot FLASH sequence. It was demonstrated that magnetisation evolution effects can lead to significant error in parameter measurement, but that this error can be eliminated by using crusher gradients to prevent evolved magnetisation from contributing to the acquired signal. However, qualitative effects are not entirely eliminated, since a significant degree of edge blurring may remain, and there is a 50% loss of SNR inherent to the crusher gradient technique. It was then shown, theoretically and experimentally, that in diffusion-weighted snapshot FLASH, the crusher gradient technique not only addresses the problem of magnetisation evolution, but also eliminates the effect of phase shifts arising during the diffusion-preparation sequence.
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Millar, Declan Andrew. "Phenomenology of searches for new neutral resonances in top quark pair production at the LHC." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/423817/.
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This report presents the research that I have done in conjunction with my supervisors Lucio Cerrito and Stefano Moretti, as well as in collaboration with Francesco Spanò, over the last three years of my studies. Chapter 6 presents work conducted as part of the e/ signature trigger group within the ATLAS collaboration. Chapter 7 presents work released in a publicly available paper, while the study discussed in chapter 8 I hope to be the subject of an upcoming publication. This thesis presents two studies considering new neutral resonances in top quark pair production at the Large Hadron Collider. Its focus is largely on charge and spin asymmetry observables sensitive to the chiral couplings of a Z′ boson. Both analyses employ a 2 ! 6 simulation accounting for all possible leading order topologies for both signal and (irreducible) top backgrounds including interference effects. The first is a parton-level analysis aimed at the lepton-plus-jets final state, using a reconstruction procedure of the (anti)top quark mass and momenta that closely mimics experimental conditions. Results show the potential of these observables to characterise the chiral couplings of the Z′ boson and distinguish between different theoretical models, and to improve the discovery potential in combination with the tt differential cross section. The second study extends to an analysis using the dilepton final state in top pair production to observe a new resonance, accounting for parton-shower, hadronisation and simulated reconstruction with the ATLAS detector. Several approaches to top reconstruction and their relative observational power are explored. Finally a study of the sources for single electron trigger inefficiencies with the ATLAS detector is presented.
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Fajardo, Luz Stella Gomez. "A search for massive resonances decaying to top quark pairs and jet trigger performance studies with the ATLAS detector at the Large Hadron Collider." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/17083.
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Diese Arbeit behandelt die Suche nach neuen Teilchen, die in Top-Quark-Paare zerfallen (t¯t). Die Analyse beruht auf Daten des ATLAS-Experiments von Proton- Proton-Kollisionen am LHC bei einer Schwerpunktsenergie von p s = 7 TeV und einer Gesamtluminosität von 2.05 fb−1. Hierzu wird der Lepton+Jets Endzustand im t¯t ! WbWb Zerfallskanal verwendet, worin ein W-Boson leptonisch und das andere hadronisch zerfällt. Das t¯t -Ereignis wird sowohl in aufgelösten als auch geboosteten Zerfallstopologien rekonstruiert. Zum ersten Mal werden die Korrelationen beider Kanäle in Form einer dritten Kategorie nutzbar gemacht, welche aus Ereignissen besteht, die in beiden Topologien selektiert wurden. Die Sensitivität der Analyse wird hierdurch erhöht. Obere Schranken bei 95% Vertrauensniveau auf den Wirkungsquerschnitt multipliziert mit der Zerfallsbreite für massive Zustände großer und kleiner Zerfallsbreite werden berechnet. Diese werden aus der Kombination der beiden Ansätze der t¯t -Rekonstruktion gewonnen. Für die Z0-Resonanz kleiner Breite reicht die beobachtete (erwartete) obere Grenze auf den Wirkungsquerschnitt von 4.85 (4.81) pb, für eine Masse von 0.6 TeV, bis 0.21 (0.13) pb, für eine Masse von 2 TeV. Eine schmale leptophobische Topcolor-Z0-Resonanzen mit einer Masse unterhalb von 1.3 TeV kann ausgeschlossen werden. Weiterhin konnten beobachtete (erwartete) obere Grenzen auch für eine breite Farboktett-Resonanz berechnet werden. Diese liegen zwischen 2.52 (2.59) pb und 0.37 (0.27) pb für Massen von 0.7 TeV bzw. 2 TeV. Breite Kaluza-Klein-Gluon-Resonanzen mit einer Masse unter 1.65 TeV können ausgeschlossen werden.This thesis presents the search for new particles that decay into top quark pairs (t¯t). The analysis is performed with the ATLAS experiment at the LHC, using an integrated luminosity of 2.05 fb−1 of proton–proton collision data, collected at a center-of-mass energy of p s = 7 TeV. The lepton plus jets final state is used in the t¯t ! WbWb decay, where one W boson decays leptonically and the other hadronically. The t¯t system is reconstructed using both resolved and boosted topologies of the top-quark decay. For the first time, correlations between the two search channels have been employed by creating a third channel with the events selected by both analyses. The sensitivity to new physics phenomena is thereby improved. Upper limits are derived on the production cross-section times branching ratio for narrow and wide massive states, at the 95 % confidence level. These are extracted by combining the two approaches of the t¯t reconstruction. For a narrow Z0 resonance, the observed (expected) upper limits range from 4.85 (4.81) pb for a mass of 0.6 TeV, to 0.21 (0.13) pb for a mass of 2 TeV. A narrow leptophobic topcolor Z0 resonance with a mass below 1.3 TeV is excluded. Observed (expected) limits are also derived for a broad color-octet resonance. They vary between 2.52 (2.59) pb and 0.37 (0.27) pb for a mass of 0.7 TeV and 2 TeV, respectively. The wide Kaluza-Klein gluon with a mass below 1.65 TeV is excluded. Another aspect of this thesis are performance studies of the level-1 jet trigger. Trigger efficiencies have been measured, using data collected by the ATLAS detector in 2010 at p s = 7 TeV. The turn-on curves obtained for a variety of jet triggers, showed good agreement between data and simulation in the plateau region. The efficiency results were used at the first stage of analyses for multi-jet cross-section measurements.
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Nicholson, Ian. "Proton electron double resonance imaging of free radicals." Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602265.
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Betz, Michael [Verfasser]. "The CERN Resonant WISP Search (CROWS) / Michael Betz." Karlsruhe : KIT Scientific Publishing, 2014. http://www.ksp.kit.edu.
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Morgenstern, Marcus Matthias. "Search for heavy resonances decaying into the fully hadronic di-tau final state with the ATLAS detector." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139662.
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The discovery of a heavy neutral particle would be a direct hint for new physics beyond the Standard Model. In this thesis searches for new heavy neutral particles decaying into two tau leptons, which further decay into hadrons, are presented. They cover neutral Higgs bosons in the context of the minimal supersymmetric extension of the Standard Model (MSSM) as well as Z′ bosons, predicted by various theories with an extended gauge sector. Both analyses are based on the full 2012 proton-proton collision dataset taken by the ATLAS experiment at the Large Hadron Collider (LHC). The extended Higgs sector in the MSSM suggests additional heavy neutral Higgs bosons which decay into tau leptons in about 10% of the time. Given that the dominant final state, φ → b¯b, suffers from tremendous QCD initiated backgrounds, the decay into two tau leptons is the most promising final state to discover such new resonances. The fully hadronic final state is the dominant one with a branching fraction of about 42%. It governs the sensitivity, in particular at high transverse momentum when the QCD multijet background becomes small.
Other theoretical extensions of the Standard Model, which are mainly driven by the concept of gauge unification, predict additional heavy particles arising from an extended underlying gauge group. Some of them further predict an enhanced coupling to fermions of the third generation. This motivates the search for Z′ bosons in the fully hadronic di-tau final state.
One major challenge in physics analyses involving tau leptons is to have an outstanding performance of trigger and identification algorithms suitable to select real tau leptons with high efficiency, while rejecting fake taus originating from quark or gluon initiated jets. In this work a new tau trigger concept based on multivariate classifiers has been developed and became the default tau trigger algorithm in 2012 data-taking. An updated tau identification technique based on the log-likelihood approach has been provided for 2011 data-taking. Furthermore, a new framework has been developed to perform the tuning of the tau identification algorithm and exploited for the optimisation for 2012 data-taking, accordingly.
The search for new heavy neutral Higgs bosons in the context of the MSSM has been performed exploiting the full 2012 dataset corresponding to an integrated luminosity of 19.5 fb−1 taken at a centre-of-mass energy of √s = 8 TeV. Updated event selection criteria and novel data-driven background estimation techniques have been developed and are suitable to increase the sensitivity of the analysis significantly. No deviations from the Standard Model prediction are observed, and thus 95% C.L. exclusion limits on the production cross section times branching ratio, σ(pp → φ) × BR(φ → ττ), are derived exploiting the CLs method. The exclusion ranges from 13.0 pb at 150GeV to 7.0 fb at 1 TeV for Higgs boson production in association with b-quarks and from 23.6 pb at 150GeV to 7.5 fb at 1 TeV for Higgs bosons produced via gluon-gluon fusion. The obtained exclusion limit on σ(pp → φ) × BR(φ → ττ) can be related to an exclusion of the MSSM parameter space in the MA-tan β-plane. Various benchmark scenario are considered. The ”standard candle” is the mhmax scenario, for which tan β values between 13.3 and 55 can be excluded at 95% C.L. in the considered mass range. Updated benchmark scenarios designed to incorporate the recently discovered SM-like Higgs boson were suggested and analysed as well. In the mhmod+ (mhmod−) scenario tan β values between 13.5 (13.3 ) and 55 (52 ) can be excluded.
Finally, a search for heavy neutral resonances in the context of Z′ bosons was performed. As in the search for new Higgs bosons, no deviation from the Standard Model prediction is observed, and hence exclusion limits on the production cross section times branching ratio, σ(pp → Z′) × BR(Z′ → ττ), and on the Z′ boson mass are derived exploiting the Bayesian approach. Z′ bosons with MZ′ < 1.9 TeV can be excluded at 95% credibility, and thus mark the strongest exclusion limit obtained in the di-tau final state by any collider experiment so far.
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O'Shea, Jacinta. "Human frontal eye fields and visual search." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:42ba15a7-ef0d-4787-a313-bc54462bb831.
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This thesis tested whether the human frontal eye fields (FEFs) have visuospatial functions that are dissociable from FEF oculomotor functions. Functional magnetic resonance imaging (fMRI) was used to localize the FEFs, and transcranial magnetic stimulation (TMS) was applied in a series of experiments to transiently disrupt information processing in the FEFs. It was shown that TMS applied over the right FEFs degrades subjects' performance on a visual conjunction search task in which eye movements were not required and were not made. A TMS timing protocol subsequently showed that computations in the FEFs that occur between 40 and 80ms after the onset of a visual search array are critical for accurate performance. This suggests that, as in the monkey, the human FEFs may accumulate and use visual evidence from extrastriate cortex, which forms the basis for accurate visuospatial discrimination. A training protocol showed that the right FEFs are no longer critical for accurate visuospatial discrimination performance once a search task has been extensively practised. This study further suggested that the FEFs may have a previously unknown role in the perception of left-right rotated shapes. A study on feature and spatial priming indicated that these two phenomena have distinct causal mechanisms. The left FEFs appear to access a spatial memory signal during the process of saccade programming. When TMS is applied during this period, the spatial priming benefit is abolished. Altogether, this thesis presents evidence that visuospatial and oculomotor functions can be dissociated in the human FEFs. The data on timing and the effects of learning correspond well with results reported in monkeys. The priming experiment offers the first evidence that the left FEFs are crucial for spatial priming, while the learning study suggests the novel hypothesis that the FEFs are crucial for left-right rotated shape perception.
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Marsden, Stephen Philip. "Search for diboson resonance production at sqrt(s) = 8 TeV with the ATLAS detector." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/search-for-diboson-resonance-production-at-sqrts--8-tev-with-the-atlas-detector(91f7ac80-2f2a-4c75-a21c-00063c527947).html.
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A search for heavy exotic diboson resonances decaying to llqq final states is presented using pp collision data collected with the ATLAS detector at the Large Hadron Collider. The analysis uses a data sample corresponding to an integrated luminosity of 20.3 fb^-1 at sqrt(s) = 8 TeV collected between April and December 2012. No significant excess of data events over the predicted Standard Model background is observed and 95% confidence level upper limits are set on the product of the production cross-section and the branching ratio for spin-2 Kaluza-Klein gravitons predicted by the bulk Randall-Sundrum model and for Extended Gauge Model W’ bosons. These results are subsequently combined with limits obtained from searches using the lvll, lvqq, and qqqq final states, and new mass limits are set on both signal models.
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Vaupel, Maren. "Measurement of the tt̄ invariant mass distribution and search for tt̄ resonances." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981638023.
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Robb, Fraser J. L. "Field-cycled proton-electron double resonance imaging of dissolved oxygen." Thesis, University of Aberdeen, 1997. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU094459.
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Field-Cycled Proton-Electron Double Resonance Imaging (FC-PEDRI) is a new imaging technique that has potential for detecting and monitoring concentrations of dissolved oxygen in aqueous solutions. This technique is based upon the magnetic interactions that can occur between nitroxide free radicals and water molecules. This thesis describes why the FC-PEDRI signal is sensitive to dissolved oxygen and explores different methods of making quantitative measurements of oxygen concentration using FC-PEDRI. It starts by developing a comprehensive theoretical model which describes all the relevant magnetic interactions which can occur between nitroxide molecules, molecules of dissolved oxygen and solvent water protons. It was found that the complicated chemical structure of nitroxide molecules can greatly affect the oxygen-sensitivity of the FC-PEDRI signal. Methods of correcting for some of these effects are discussed. The instrumentation necessary to perform FC-PEDRI oximetry is also described, as is the implementation of oxygen-sensitive FC-PEDRI pulse sequences. The success of these sequences was found to be strongly dependent on the performance of the field-cycling apparatus. Two different FC-PEDRI instruments are described in this thesis. The construction and commissioning of one of these instruments is fully discussed. This instrument was large enough to allow in-vivo FC-PEDRI experiments to be undertaken and was based upon the use of novel field-cycling control electronics. The improved operation of this machine, in comparison to that of the older instrument, allowed the oxygen-sensitive pulse sequences developed in this thesis to be performed much more satisfactorily.
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Alecci, Marcello. "New magnetic resonance techniques for in vivo free radical detection." Thesis, University of Aberdeen, 1998. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU106309.
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Naturally occurring free radicals are involved in normal metabolism and in a number of conditions such as myocardial ischaemia, inflammation, ageing and cancer. Stable free radicals can be introduced into animals and used as "tracers" to study renal function, integrity of the blood-brain barrier, subcutaneous neoplasms, extra vascular viscosity in tumour tissues, oxygen concentration in cells and tissues. They have also been studied as contrast enhancing systems in Magnetic Resonance Imaging (MRI). At present, two closely-related magnetic resonance techniques exist which are capable of imaging free radicals, namely Proton-Electron Double-Resonance Imaging (PEDRI) and Electron Paramagnetic Resonance Imaging (EPRI). These techniques are at the beginning of their development and a substantial improvement of their performances is crucial for future applications. The aim of this thesis was to investigate new methods for improving PEDRI and EPRI techniques at radio frequencies. In summary, the main topics can be grouped as follows: (i) A pulsed dynamic nuclear polarisation (DNP) technique at 10 mT was developed and a theoretical model for calculation of the DNP enhancement with a train of EPR pulses was proposed. It was shown experimentally that the use of pulsed DNP techniques at 10 mT can increase the enhancement and/or decrease the required average applied RF power to samples containing free radicals in solution. (ii) A simultaneous multiple CW EPR irradiation technique for PEDRI at 10 mT was introduced. A novel EPR resonator and a PEDRI apparatus suitable for multiple-frequency EPR irradiation experiments were designed and tested. It was shown that simultaneous multiple CW EPR irradiation increases the PEDRI sensitivity (up to a factor of three with nitroxides in solution). (iii) Novel radio frequency pulsed EPR instrumentation was developed. This apparatus has a submicrosecond dead time and was developed for fast direct detection of free radicals in large samples. However, its field of applicability is very broad and, for example, it can be used for pulsed NMR imaging of solids.
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McCallum, Stephen John. "A multimodality magnetic resonance system for studying free radicals in biological systems." Thesis, University of Aberdeen, 1997. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU090119.
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Free radicals are defined as molecules with one or more unpaired electrons in their outer orbits. They have been implicated in a large number of disease states and consequently there is increasing interest in detecting them in vivo. Having an un-cancelled electron spin, free radicals are amenable to magnetic resonance experiments. For reasons of sensitivity commercially available electron paramagnetic resonance (EPR) spectrometers operate in the X-band (9 GHz). Such frequencies are unsuitable for large biological samples because of excessive electromagnetic losses. This thesis describes the development of a radio frequency continuous wave (RFCW) EPR spectrometer operating around 280 MHz suitable for in vivo studies. The instrument is based around an existing low field NMR imager. The spectrometer includes both automatic frequency control and automatic coupling systems to combat the problems of animal motion. The instrument has been able to detect free radicals in living animals. PEDRI is a technique that can provide high resolution images showing free radical distribution in living systems. The method is based on conventional pulsed NMR imaging combined with dynamic nuclear polarisation The disadvantage of PEDRI is that it is difficult to obtain spectral information such as EPR line-width and g-factor. These parameters are easy to obtain by CW-EPR, and can give useful information. A further development was the combining of the RF CW-EPR instrument with a PEDRI imager to produce a multimodality instrument capable of sequential PEDRI and CW-EPR on the same sample. Switch-over between the two modes of operation takes less than 5 seconds. This instrument combines the advantages of the two types of free radical detection in a single instrument providing an extremely useful and flexible tool.
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Brookes, Jason A. "Quantitation of contrast enhancement in dynamic magnetic resonance imaging of the breast." Thesis, University of Aberdeen, 1996. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU090114.
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This thesis explores issues relating to the quantitation of both signal enhancement and contrast agent uptake, along with problems associated with such quantitation, with the aim of improving the specificity of dynamic, contrast enhanced breast MRI. A variable flip angle technique for measuring T1 in vivo was implemented using 2D and 3D FLASH sequences, in order to monitor the differential relaxation rate following injection of contrast agent. Experiments (with phantom objects) investigating sources of error in these techniques found that (i) the rf transmit power calibration automatically performed by the imaging system was 13.5% in error, (ii) significant non-uniformity in the rf transmit field existed over the breast coil volume and (iii) a 2D FLASH sequence developed locally from an editable scout sequence was significantly more accurate at measuring T1 than a commercially supplied 2D FLASH sequence. Since the in vivo measurement of T1 requires complicated imaging protocols and data analysis, two simple indices commonly used to quantitate signal enhancement were evaluated by computer simulation and comparison in a group of patients. The postulate that the index least influenced by pre-contrast tissue T1 (when using a contrast enhanced gradient echo imaging protocol) would be better able to correctly classify an undiagnosed lesion as either benign or malignant was used to evaluate which index was the most appropriate for quantitating signal enhancement in breast MRI. An index which normalised the difference between pre- and post-contrast signal to the fat signal intensity proved to be the better of the two indices. One problem with this index, however, is that it is sensitive to variations in fat signal through the breast. A simple uniformity correction scheme was implemented to reduce this problem and tested on both phantom and patient image data sets.
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Ruiz, Vargas José Cupertino [UNESP]. "Search for new resonances in the merged jet plus dilepton final state in CMS." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/150892.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Na Organização Europeia para a Pesquisa Nuclear (CERN), o Large Hadron Collider (LHC) colide grupos de prótons 40 milhões de vezes por segundo a uma energia de 13 TeV. Operando junto ao LHC, o Compact Muon Solenoid (CMS) é um detector projetado para identificar uma ampla gama de partículas produzidas nessas colisões. As partículas produzidas em cada colisão são observadas nos subdetectores na busca de pistas sobre a Natureza no seu nível mais fundamental. Apesar do modelo padrão das partículas elementares ter sido testado em uma variedade de experimentos de altas energias, um dos principais objetivos do LHC é a busca de uma nova física além daquela prevista pela teoria existente. Nesse trabalho analisamos os dados de colisões próton-próton produzidos pelo LHC operando com energia de centro de massa de 13 TeV e coletados pelo CMS em 2015. O presente estudo envolve a busca de uma ressonância X não observada previamente, decaindo em um par de bósons vetoriais. Os resultados são interpretados no contexto do modelo de dimensões extras deformadas de Randall-Sundrum, distinguindo as hipóteses de fundo (modelo padrão) e fundo mais sinal (modelo padrão + graviton). Nenhuma evidência da existência de uma partícula com as características do graviton de Randall-Sundrum foi encontrada.
At the European Organization for Nuclear Research (CERN), the Large Hadron Collider (LHC) smashes groups of protons 40 million times per second at an energy of 13 TeV. Operating at the LHC, the Compact Muon Solenoid (CMS) is a multipurpose detector conceived to identify a large variety of particles produced in such collisions. The produced particles are observed at the sub-detectors in search of clues about Nature at the most fundamental level. In spite of the impressive agreement of the standard model with all the experimental results obtained so far, one of the main aims of the LHC is the search of new physics beyond the one foreseen by this theoretical model. In this work, we analyze proton–proton collisions delivered by the LHC operating at centre-of-mass energy of 13 TeV and collected by CMS during 2015. The channel under study involves the search for an unknown resonance X decaying into a pair of vector bosons. The results are interpreted in the context of the Randall-Sundrum warped extra-dimensional model, distinguishing between the hypotheses of background only (standard model) and background plus signal (standard model + graviton). No evidence of the existence of a graviton-like particle was found.
FAPESP: 2012/24593-8
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Ruiz, Vargas José Cupertino. "Search for new resonances in the merged jet plus dilepton final state in CMS /." São Paulo, 2017. http://hdl.handle.net/11449/150892.
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Orientador: Sérgio Ferraz NovaesCoorientador: Thiago R. F. P. Tomei
Banca: Alexandre Alves
Banca: Antonio Vilela Pereira
Banca: Gilvan Augusto Alves
Banca: Murilo Santana Rangel
Resumo: Na Organização Europeia para a Pesquisa Nuclear (CERN), o Large Hadron Collider (LHC) colide grupos de prótons 40 milhões de vezes por segundo a uma energia de 13 TeV. Operando junto ao LHC, o Compact Muon Solenoid (CMS) é um detector projetado para identificar uma ampla gama de partículas produzidas nessas colisões. As partículas produzidas em cada colisão são observadas nos subdetectores na busca de pistas sobre a Natureza no seu nível mais fundamental. Apesar do modelo padrão das partículas elementares ter sido testado em uma variedade de experimentos de altas energias, um dos principais objetivos do LHC é a busca de uma nova física além daquela prevista pela teoria existente. Nesse trabalho analisamos os dados de colisões próton-próton produzidos pelo LHC operando com energia de centro de massa de 13 TeV e coletados pelo CMS em 2015. O presente estudo envolve a busca de uma ressonância X não observada previamente, decaindo em um par de bósons vetoriais. Os resultados são interpretados no contexto do modelo de dimensões extras deformadas de Randall-Sundrum, distinguindo as hipóteses de fundo (modelo padrão) e fundo mais sinal (modelo padrão + graviton). Nenhuma evidência da existência de uma partícula com as características do graviton de Randall-Sundrum foi encontrada. Limites superiores com nível de confiança de 95% são estabelecidos para a seção de choque de produção da ressonância X decaindo em um par de bosons Z, para valores de massa MX no intervalo 800 - 3000 GeV. A exclusão esperada (observada) no valor de massa MX = 800 GeV é 154 fb (93 fb); para o valor de massa MX = 3000 GeV o valor de exclusão esperado (observado) diminui para 19 fb (15 fb). Um excesso com significância global igual a 2s é observado no ponto de massa MX = 1000 GeV.
Abstract: At the European Organization for Nuclear Research (CERN), the Large Hadron Collider (LHC) smashes groups of protons 40 million times per second at an energy of 13 TeV. Operating at the LHC, the Compact Muon Solenoid (CMS) is a multipurpose detector conceived to identify a large variety of particles produced in such collisions. The produced particles are observed at the sub-detectors in search of clues about Nature at the most fundamental level. In spite of the impressive agreement of the standard model with all the experimental results obtained so far, one of the main aims of the LHC is the search of new physics beyond the one foreseen by this theoretical model. In this work, we analyze proton-proton collisions delivered by the LHC operating at centre-of-mass energy of 13 TeV and collected by CMS during 2015. The channel under study involves the search for an unknown resonance X decaying into a pair of vector bosons. The results are interpreted in the context of the Randall-Sundrum warped extra-dimensional model, distinguishing between the hypotheses of background only (standard model) and background plus signal (standard model + graviton). No evidence of the existence of a graviton-like particle was found. Upper limits at 95% confidence level are set for the production cross section of a resonance X decaying to a pair of Z bosons, for values of mass MX in the range between 800 - 3000 GeV. The limit expected (observed) at MX = 800 GeV is 154 fb (93 fb); for the mass point MX = 3000 GeV the limit expected (observed) decreases to 19 fb (15 fb). A localised excess with global significance equal to 2s is observed in the mass point MX = 1000 GeV.
Doutor
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Schäfer, Daniela [Verfasser]. "Suche nach Zwei-Boson-Resonanzen im vollhadronischen Endzustand mit dem CMS-Detektor = Search for Diboson Resonances in the Full-Hadronic Final State with the CMS Detector at $\sqrts}$ = 13 TeV / Daniela Schäfer." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1203211880/34.
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Semple, Scott I. K. "Clinical cardiac functional MRI." Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602018.
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The purpose of this project was to assess techniques which could be implemented in clinical cardiac MRI using a moderate gradient performance imaging system in order to aid in the assessment of myocardial function. Possible improvements in image contrast were assessed using four different magnetisation preparation schemes applied prior to MR image acquisition in order to aid in the delineation of myocardial borders, and therefore improve cardiac image assessment quality. The usefulness of several novel T2*-weighted acquisition techniques were assessed in clinical cardiac applications in order to indirectly assess myocardial perfusion. Four magnetisation preparation schemes were applied in order to attempt to improve image contrast in short axis gradient-echo cardiac MRI; T2, T1, Magnetisation Transfer Contrast (MTC), and Double Inversion (DI). The T2, and preparation schemes proved to be the most effective, showing an initial improvement in image contrast by approximately 100% and proving effective in improving image contrast over the entire imaging duration {550 ms through the cardiac cycle). The MTC preparation scheme showed a 50% improvement in image contrast, again being effective over the entire imaging duration. The DI preparation scheme proved useful in creating a black blood gradient-echo image but showed no improvement in contrast throughout the imaging duration (since the DI preparation technique is essentially a 'snapshot' technique). Recent developments in cardiac MRI have moved towards assessment of myocardial perfusion, using first-pass contrast-enhancement imaging. This approach requires assessment of a large enough volume of the heart to allow assessment of perfusion as well as retaining a high temporal resolution of 7 or 2 seconds, and therefore a more modem high performance imaging system. For moderate performance gradient MR systems an alternative method of assessing myocardial perfusion is therefore required. Several novel techniques to assess myocardial T2* values in order to indirectly infer myocardial perfusion are introduced. The use of an original multi-echo gradient-echo imaging sequence to acquire T2* pixel-maps was investigated in phantoms and compared with commercially available sequences in order to validate its use.
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Swedish, Stephen. "Searches for new resonances decaying to top-antitop quark pairs with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50169.
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This work presents the results of two analyses searching for massive resonances decaying to top-antitop quark pairs in sqrt(s) = 7 TeV proton-proton collisions measured with the ATLAS detector at the CERN Large Hadron Collider. The peculiar position of the top-quark within the Standard Model, as the most massive particle, motivates many theories predicting the existence of new massive particles that couple strongly to top-quarks. These particles may manifest themselves at the LHC as new massive resonances decaying to top-antitop quark pairs. An analysis conducted on the first 2.04/fb^-¹ of data collected in 2011 searched for resonances in the subset of top-pair events where the W-bosons from each top decay decayed leptonically to a final state electron or muon. A second analysis conducted on the full 4.7/fb^-¹ of 2011 data searched for resonances in the subset of top-quark pair events where W-bosons from each top decay decayed hadronically to a diquark pair. The analysis focused on the case were each top-quark is sufficiently boosted such that the resultant fully hadronic system is highly collimated, and reconstructable as a single hadronic jet with large angular separation. In each analysis, the leptophobic Z' from topcolor assisted technicolor models, and the KK-gluon from Randall-Sundrum warped extra-dimension models were chosen as benchmarks to test for the presence of narrow and wide resonances respectively. No significant deviation from the Standard Model was observed in either analysis. The results were used to set 95% C.L. upper limits on the cross-section times branching ratio to top-quark pairs as a function of resonance mass for each benchmark model. The existence of a Randall-Sundrum KK-gluon was excluded at the 95% C.L. over the mass range 500 to 1620 GeV.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Michetti, Michele. "Search for ttbar resonances at sqrt(s) = 8 TeV with the CMS experiment at LHC." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/12229/.
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This work concerns the search for the production of heavy resonances decaying into ttbar pairs at a the center-of-mass energy √s = 8 TeV in the CMS experiment at LHC.
After the Higgs boson discovery, a persisting issue in the Standard Model is the squared divergencies of the Higgs mass, that generate the “hierarchy problem”. This divergence is mitigated by the Supersimmetry or, in other models, introducing the Kaluza-Klein gluonic resonances or Z massive resonances with higher coupling with the most massive particles. For this reason, the ttbar decay is the channel with the highest cross section. The models predict a mass of these resonances between 700 GeV and some TeV, and production cross sections around some picobarns.
The CMS data collected at √s = 8 TeV center-of-mass energy with integrated luminosity L= 19.5 fb^(-1) represent a large sample of data on which it is possible to look for a possible tt resonances.
In this thesis, the search is performed in the all-jets channel with reference to the resolved event topology characterised by 6 or more jets in the final state.
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Viel, Simon. "Search for new neutral high-mass resonances decaying into muon pairs with the ATLAS detector." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/49948.
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The question of physics beyond the Standard Model remains as crucial as it was before the discovery of a Higgs boson at the Large Hadron Collider, as the theoretical and experimental shortcomings of the Standard Model remain unresolved. Indeed, theoretical problems such as the hierarchy of energy scales, the Higgs mass fine-tuning and the large number of postulated parameters need to be addressed, while the experimental observations of dark matter, dark energy and neutrino masses are not explained by the Standard Model. Many hypotheses addressing these issues predict the existence of new neutral high-mass resonances decaying into muon pairs.
This dissertation documents a search for this process using 25.5 inverse femtobarns of proton-proton collision data collected by the ATLAS experiment in Run‑I of the Large Hadron Collider. After evaluating the performance of the detector for reconstructing muons at very high momentum, the event yields observed as a function of the invariant mass of muon pairs are compared with expected values from Standard Model processes.
The observed yields are found to be in good agreement with Standard Model predictions, and no significant excess of events is found. New gauge bosons with couplings to fermions equal to these of the Standard Model Z boson and with masses lower than 2.53 TeV are therefore excluded at 95% confidence level. A statistical combination with the results of the search for the same particle decaying into electron pairs yields a lower mass limit of 2.90 TeV at 95% confidence level. Limits are also placed in the context of two classes of models inspired by Grand Unification Theories: gauge theories with the E₆ symmetry group, as well as Minimal Z' Models.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Thomas, Laurent. "Search for new heavy narrow resonances decaying into a dielectron pair with the CMS detector." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209221.
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Le sujet de la présente thèse porte sur la recherche de nouvelles particules très massives se désintégrant en une paire électron-positron avec le détecteur CMS.Le démarrage en 2010 du Large Hadron Collider au CERN marque le début d'une nouvelle ère en physique des particules. L'énergie et l'intensité de ses faisceaux de protons, inégalées à ce jour, offre en effet la possibilité d'étudier les lois décrivant les constituants ultimes de la matière et leurs interactions à des énergies jusqu'alors inaccessibles et d'étudier des processus rares.
La découverte récente par les expériences ATLAS et CMS du boson scalaire prédit par la théorie de la brisure de symétrie électro-faible constitue ainsi la première percée du programme de recherche du LHC et confirme la théorie actuelle décrivant la physique subatomique, le Modèle Standard.
Il est cependant largement admis que cette théorie, bien que hautement prédictive et jamais mise en défaut expérimentalement jusqu'à présent, ne constitue qu'une approximation à basse énergie d'une théorie plus fondamentale.
Cette thèse décrit la recherche de nouvelles particules, prédites par plusieurs modèles au delà du Modèle Standard, via leur désintégration en une paire électron-positron de haute énergie.
La reconstruction et la sélection des électrons de haute énergie par le détecteur CMS sont des éléments centraux de cette analyse et sont étudiées en détail. Divers critères sont développés afin de distinguer les électrons des autres types d'objets physiques produits lors de collisions de protons, tels que les jets. L'intensité des faisceaux du LHC est telle que plusieurs collisions ont lieu simultanément dans le détecteur et il est montré que l'efficacité de sélection des électrons dépend fortement du nombre de ces interactions. Une technique est donc mise au point pour corriger cet effet.
Une méthode pour mesurer l'efficacité de la sélection directement sur les données est également développée. Celle-ci permet de confirmer les mesures obtenues à partir de simulations, jusqu'à des impulsions transverses de plusieurs centaines de GeV.
Le spectre de masse des paires diélectron est établi pour les données enregistrées en 2012 à une énergie dans le centre de masse des protons de 8 TeV, et un excès localisé d'événements est recherché. Aucune déviation significative par rapport au bruit de fonds attendu n'est observée et des limites très contraignantes sont établies sur le rapport de la section efficace de production d'une nouvelle résonance diélectronique et de celle mesurée au pic du boson Z. Ces résultats sont utilisés pour fixer des limites inférieures sur la masse de nouvelles particules prédites par certains modèles.
Le redémarrage du LHC en 2015 avec une énergie de 6.5 TeV par faisceau de proton élargira fortement le potentiel de découverte de ces résonances. En cas de découverte d'un signal, ses propriétés (telles que le spin ou l'asymétrie avant-arrière) seront étudiées avec attention. Des projections sur la précision qui pourrait alors être atteinte pour ces mesures sont donc finalement présentées en fonction de la luminosité intégrée collectée.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Chapleau, Bertrand. "Search for top-antitop quark resonances with the ATLAS detector at the Large Hadron Collider." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123013.
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The intriguing nature of the top quark, by far the heaviest particle in the Standard Model of particle physics, has motivated the development of many theoretical extensions predicting the existence of new massive particles decaying to a pair of top-antitop quarks. The production of these hypothetical particles in proton-proton collisions at the Large Hadron Collider would reveal itself as a resonance in the expected smooth distribution of the top-antitop quark invariant mass. This thesis presents a search for such a new heavy particle decaying to a pair of top-antitop quarks in the semi-leptonic final state. The analyzed data sample amounts to a total of 4.6 fb−1 at a proton-proton collision center-of-mass energy of 7 TeV. Novel techniques specifically tailored to the identification of the decay products of highly energetic top quarks are developed and used. No evidence for resonant production of pairs of top-antitop quarks is found and, as a result, constraints are set on two theoretical models. Upper limits on the production cross-section times branching ratio are established at a 95% credibility level for a leptophobic Z′ boson from the Topcolor model, and a Kaluza-Klein gluon from the Randall-Sundrum model. The Z′ boson and the Kaluza-Klein gluon are excluded to exist (at a 95% credibility level) in the mass ranges 0.8-1.65 TeV and 0.8-1.88 TeV, respectively. The constraints de- rived in this thesis on the two theoretical models are more stringent than the ones obtained at other experiments, thanks to the large center-of-mass energy and the dedicated high-energy top quark identification techniques used.La nature intrigante du quark top, de loin la particule élémentaire la plus lourde du Modèle standard de la physique des particules, a motivé le développement de nom-breuses théories prédisant l'existence de nouvelles particules massives se désintégrant en une paire de quarks top-antitop. La production de ces particules hypoth étiques dans des collisions de type proton-proton au Grand collisionneur de hadrons (LHC) se manifesterait sous la forme d'une résonance dans la distribution de la masse invariante des paires de quarks top-antitop. La présente thèse consiste en une recherche d'une telle particule se désintégrant en une paire de quarks top-antitop dans l'état final dit semi-leptonique. La taille de l'échantillon de données analysé équivaut à 4.6 fb−1 à une énergie de centre de masse des collisions proton-proton de 7 TeV. Des techniques novatrices d'identification des produits de désintégrations de quarks top à grande énergie sont développées et utilisées. La présence d'une résonance dans la production de paires de quarks top-antitop n'a pu être établie et, conséquemment, des contraintes sont dérivées sur deux modèles théoriques. Des limites supérieures sur la section efficace de production multipliée par le rapport de branchement sont établies avec un niveau de crédibilité de 95% pour un boson Z′ leptophobique du modèle Topcolor, ainsi que pour un gluon Kaluza-Klein du modèle Randall-Sundrum. Le boson Z′ et le gluon Kaluza-Klein sont proscrits (avec un niveau de crédibilité de 95%) dans la région de masse 0.8-1.65 TeV et 0.8-1.88 TeV respectivement. Grâce à la grande énergie de centre de masse ainsi qu'aux techniques spécialisées d'identification des quarks top de grande énergie, les contraintes dérivées dans la présente thèse sur les deux modèles théoriques ici considérés sont plus restrictives que celles obtenues par le biais d'autres expériences.
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Damp, Johannes Frederic [Verfasser]. "Search for Dijet Resonances with the Level-1 Topological Processor at ATLAS / Johannes Frederic Damp." Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2021. http://d-nb.info/1227048726/34.
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Yeung, David. "Dual-tuned radiofrequency coils for field-cycled proton-electron double resonance imaging of free radicals." Thesis, University of Aberdeen, 1995. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU078721.
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Field-cycled proton-electron double-resonance imaging (FC-PEDRI) is a technique developed to image the distribution of free radicals in biological samples. This technique is based on the Overhauser Effect that causes an enhancement in the NMR signal by saturating the ESR resonance of unpaired electrons in the sample. FC-PEDRI requires two sources of RF irradiations. To improve the sensitivity and to reduce power deposition in samples, new dual-tuned single coil designs were needed since existing dual-tuned single-coil designs known in the literature cannot operate at two widely separated frequencies. The theory of double-tuned circuits was examined and new circuit models were developed to identify the design requirements. Four new dual-tuned RF coils were developed, namely a dual-tuned split solenoidal coil (2.5 and 78 MHz), a combined saddle-birdcage (CS-B) coil (2.5 and 110 MHz), a 3-endring (3-ER) birdcage (2.5 and 56 MHz) and a 4-endring (4-ER) birdcage (2.5 and 74 MHz). A prototype coil for each design was built for performance evaluation studies and the parameters evaluated were: the Q factors, the signal-to-noise ratio, the transmit sensitivity and the field uniformity. The performance of the NMR-mode of the 3-ER and 4-ER designs was poor because the inherently low-inductance of the birdcage meant that high-value capacitors with high dissipation factors had to be used in the fabrication. A new construction method named as the multilayer self capacitance (MLSC) technique was developed to improve the efficiency of the 4-ER design by creating efficient capacitors within the conductors of the coil itself. The unloaded Q factor of the optimised 4-ER birdcage using the MLSC technique was 267 compared to 100 when commercial capacitors were used.
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Livermore, Sarah Stephanie Alexandra. "A search for massive top quark resonances with the ATLAS detector at the Large Hadron Collider." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:c826ed7f-1566-4a93-8675-d32ed3b97f7d.
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This thesis presents a search for resonant production of top-antitop quark pairs in final states containing at least one electron or muon. A number of beyond the standard model (BSM) theories incorporate a specific role for the top quark, resulting in resonances that preferentially decay to t(bar over t) pairs. The data sample analysed corresponds to an integrated luminosity of 2.05 fb-1 recorded during 2011 using the ATLAS detector at the Large Hadron Collider. The proton-proton centre-of-mass energy was 7 TeV. The search is tailored towards heavy resonances at the TeV-scale which therefore decay to top quarks with high transverse momentum. Large hadronic jets are used to reconstruct the energy carried by the hadrons and the substructure of these jets is studied in order to identify hadronically decaying top quarks. The reconstruction can therefore proceed even if the decay products of the top quark are highly collimated. This study represents the first use of jet substructure techniques in a search for t(bar over t) resonances using hadron-hadron collision data. The invariant mass of the reconstructed t(bar over t) pair is used to test compatibility of the data with the standard model prediction. No evidence for t(bar over t) resonances is found. Upper limits are derived on the production cross-section times branching ratio for narrow and wide resonant states, at the 95 % credibility level. An upper limit of 0.61 (0.65) pb is set for a narrow (wide) resonance with a mass of 1 TeV. Two specific BSM models are excluded within certain mass ranges: the narrow leptophobic Z' boson with mass 600 - 1150 GeV and the wide Kaluza-Klein gluon with a mass below 1.5 TeV. These results represent a significant improvement on those of previous searches performed at the ATLAS experiment, which did not use jet substructure techniques. In addition, the possibility of using jets which decrease in size as their transverse momentum increases is investigated using simulated data. The yield of events due to resonant t(bar over t) production increases by approximately 20 % compared to when using jets of fixed size. Furthermore, the resolution of the invariant mass of the reconstructed t(bar over t) pair is found to improve by almost one fifth. It is recommended that a calibration scheme be developed for these variable-sized jets, so that their potential to improve the sensitivity to t(bar over t) resonances can be investigated further.
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Reis, Thomas. "Search for new massive resonances decaying to dielectrons or electron-muon pairs with the CMS detector." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209131.
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Le sujet de cette thèse porte sur la recherche de nouvelles résonances massives se désintégrant en une paire d’électrons ou une paire électron-muon avec le détecteur CMS, installé auprès du Grand Collisionneur du Hadrons (LHC) au CERN. Les données analysées correspondent à l’ensemble des collisions proton-proton enregistrées par le détecteur en 2012 à une énergie dans le centre de masse de 8 TeV. Après une brève introduction au modèle standard des particules élémentaires et à quelques unes des théories allant au-delà, le LHC et le détecteur CMS sont présentés. La reconstruction des différentes particules créées lors des collisions, en particulier des électrons et muons de haute énergie, est ensuite discutée. Deux analyses séparées sont menées.La première consiste en la recherche d’une nouvelle résonance étroite, plus massive que le boson Z, dans le spectre de masse invariante des paires d’électrons, dont la principale contribution, dans le modèle standard, provient du processus de Drell–Yan. De telles résonances sont notamment prédites par des modèles dits de grande unification ou à dimensions spatiales supplémentaires. Le bruit de fond provenant des processus du modèle standard étant réduit dans la région étudiée, quelques événements localisés peuvent suffire pour mener à une découverte, et la sélection des électrons est optimisée afin de ne perdre aussi peu d’événements que possible. Les différentes contributions des bruits de fond sont partiellement estimées à partir de simulations. Une méthode basée sur le spectre de masse invariante des paires électron-muon mesuré dans les données est développée pour valider la contribution du second bruit de fond en terme d’importance. Aucun excès n’est observé par rapport aux prédictions du modèle standard et des limites supérieures à 95% de niveau de confiance sont placées sur le rapport entre la section efficace de production multipliée par le rapport de branchement d’une nouvelle résonance et celle au pic du boson Z. Ces limites sont ensuite converties en limites inférieures sur la masse de différentes particules hypothétiques de spin 1 ou de spin 2.
La seconde analyse consiste en une recherche de résonances massives et étroites dans le spectre de masse invariante des paires électron-muon. De telles résonances briseraient la conservation du nombre leptonique tel que prédit par le modèle standard. Cette possibilité existe cependant dans certains modèles de nouvelle physique. C’est notamment le cas pour un modèle à dimensions supplémentaires où apparaissent des nouveaux bosons neutres lourds. La sélection des événements demande un électron de haute énergie comme dans l’analyse précédente, et un muon de grande impulsion transverse. La stratégie de recherche est similaire au cas des paires d’électrons :le fait de rechercher un signal étroit rend l’analyse statistique très peu sensible aux erreurs systématiques affectant la normalisation absolue du spectre de masse électron-muon. Comme aucune déviation significative n’est observée par rapport aux prévisions du modèle standard, des limites supérieures sur la section efficace multipliée par le rapport de branchement sont établies pour le modèle à dimensions spatiales supplémentaires. Étant données les faibles valeurs théoriques de la section efficace de production des résonances violant la conservation de la saveur dans ce modèle, la quantité de données analysées ne permet pas d’en déduire une limite inférieure sur leur masse. Cette analyse représente néanmoins la première recherche directe avec l’expérience CMS, de bosons massifs, se désintégrant avec violation du nombre leptonique, en une paire électron-muon.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Haj, Ahmad Wael [Verfasser]. "Search for top quark pair resonances with the CMS detector at the LHC / Wael Haj Ahmad." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1037106644/34.
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St, John Jason Michael. "A search for new resonances with the dijet angular ratio using the Compact Muon Solenoid Experiment." Thesis, Boston University, 2012. https://hdl.handle.net/2144/31606.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
A search for dijet resonances is performed using 2.2 fb-1 of proton-proton collision data at [Special characters omitted.] = 7 TeV recorded by the CMS detector at CERN. The study is based on the dijet angular ratio, the ratio of the number of events with the two leading jets having pseudorapidity difference |Δη| < 1.3 to the number of events with 1.3 < |Δη| < 3.0. Models of new resonances which decay into two jets typically predict dijet angular distributions and hence, values of the dijet angular ratio which differ from standard model processes. We thus use the measurement of the angular ratio as a function of mass to set limits on the cross sections of new spin-1⁄2 quark-gluon resonances. We exclude excited quarks of mass less than 3.2 TeV at 95% confidence level, where a limit of 2.8 TeV is expected.
2031-01-01
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Walshe, Joseph Michael. "Resonant scattering studies of 24Mg and 28Mg and the search for nuclear water." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6514/.
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The neutron-rich nucleus 28Mg has been studied for the first time above the particle decay threshold using α-particle resonant scattering with a beam of radioactive 24Ne ions from the SPIRAL facility at GANIL. The thick target inverse kinematics technique was used to permit measurement of the differential cross section at 180◦ in the centre-of-mass frame, for the excitation energy region from 15 to 21 MeV, with a single beam energy. Since no previous experimental data exist with which to compare the current work, data were also taken for 24Mg using a 20Ne beam with the same experimental set-up. Comparison of these data with previous work yields excellent agreement and so validates the data collection method. In 28Mg, energies and widths of thirteen new states are reported with relative strengths given for ten of these. For two states, spin-parity assignments are made and it is found, by calculation of the α-decay branching ratios and comparison to a theoretical model, that these two states do not appear to be strongly α clustered. The underlying structure of 28Mg in this region is therefore not clear, and further experimental work is required in order to establish a full understanding, with a particular focus on the energy resolution of the measurement. The experimental technique is a powerful tool for the study of α elastic scattering cross sections, and combined with new radioactive beam facilities will prove an effective method of investigating α clustering in a wide range of unstable nuclei.
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Czodrowski, Patrick. "Search for Charged Higgs Bosons with the ATLAS Detector at the LHC." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-119770.
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Die Entdeckung eines geladenen Higgs-Bosons, H+, wäre ein unbestreitbarer Nachweis von Physik jenseits des Standardmodells. In der vorliegenden Arbeit wird die Suche nach dem H+ mit Hilfe von Proton-Proton-Kollisionen, welche im Jahr 2011 mit dem ATLAS Experiment am Large Hadron Collider, LHC, des CERN aufgenommen wurden, beschrieben. Im Rahmen dieser Arbeit wurde eine überarbeitete Analyse der Suche nach geladenen Higgs-Bosonen, die eine Verhältnismethode anwendet und damit die Sensitivität des traditionell direkten Suchansatzes stark verbessert, durchgeführt. Leichte geladene Higgs-Bosonen, welche eine Masse geringer als die des Top-Quarks aufweisen, können aus einem Top-Quark-Zerfall hervorgehen. Im Gegensatz zu den schweren geladenen Higgs-Bosonen sind die leichten aufgrund des hohen Produktionswirkungsquerschnitts von Top-Quark-Paaren am LHC potenziell mit den ersten Daten des Experiments beobachtbar.
In den meisten Theorien und Szenarien sowie dem größten Bereich ihres Phasenraumes zerfallen leichte geladene Higgs-Bosonen meist im H± → τ±ν Kanal. Demzufolge spielen sowohl die τ-Identifikation als auch die τ-Fehlidentifikation eine besondere Rolle für die Suche nach geladenen Higgs-Bosonen. Eigens für die Ermittlung der Fehlidentifikationswahrscheinlichkeiten von Elektronen als hadronisch zerfallende τ-Leptonen wurde eine “tag-and-probe”-Methode, basierend auf Z → ee Ereignissen, entwickelt. Diese Messungen sind mit den allerersten Daten durchgeführt worden. Dabei haben diese einerseits für alle Analysen, welche die Elektronenveto-Algorithmen der τ-Identifikation nutzen, essenzielle Skalenfaktoren hervorgebracht. Andererseits wurde, beruhend auf diesen Ergebnissen, eine datenbasierte Abschätzungsmethode entwickelt und für die Untergründe der geladenen Higgs-Boson-Suche, die von der Fehlidentifikation von Elektronen als hadronisch zerfallende τ-Leptonen stammen, erfolgreich implementiert.
Im Rahmen dieser Arbeit wurden Triggerstudien, mit dem Ziel höchstmögliche Signaleffizienzen zu gewährleisten, durchgeführt. Neuartige Triggerobjekte, basierend auf einer Kombination aus τ-Trigger und fehlender transversaler Energie-Trigger, wurden entworfen, überprüft und in das Triggermenü für die Datennahme im Jahr 2012 aufgenommen. Eine direkte Suche nach dem geladenen Higgs-Boson wurde in drei Kanälen mit einem τ-Lepton im Endzustand unter Berücksichtigung des gesamten Datensatzes des Jahres 2011 durchgeführt. Da kein signifikanter Überschuss, der von den Vorhersagen des Standardmodells abweicht, in den Daten beobachtet wurde, sind obere Ausschlussgrenzen auf B(t → bH+) gesetzt worden.
Letztlich ist die Analyse des Kanals mit einem hadronisch zerfallenden τ-Lepton und einem Myon oder Elektron im Endzustand des tt ̄-Zerfalls, unter Anwendung der sogenannten Verhältnismethode, wiederholt worden. Diese Methode misst Verhältnisse von Ereignisausbeuten, anstatt die Verteilungen diskriminierender Variablen zu evaluieren. Folglich kürzen sich die meisten dominant beitragenden systematischen Unsicherheiten intrinsisch heraus. Die Daten stimmen mit den Vorhersagen des Standardmodells überein. Durch Zuhilfenahme der Verhältnismethode wurden die oberen Ausschlussgrenzen, im Vergleich zur direkten Suche, signifikant verbessert. Die Resultate der Verhältnismethode sind mit denen der direkten Suche, welche ein hadronisch zerfallendes τ-Lepton und zwei Jets im Endzustand des tt ̄-Zerfalls nutzt, kombiniert worden. Auf diese Art und Weise konnten obere Ausschlussgrenzen auf B(t → bH+) in einem Bereich von 0,8 %–3,4 % für geladene Higgs-Bosonen in einem Massenbereich für m_H+ zwischen 90 GeV und 160 GeV gesetzt werden.
Sollte das Minimal Supersymmetrische Standardmodell (MSSM) in der Natur realisiert sein, so haben die hier ermittelten oberen Ausschlussgrenzen auf B(t → bH+) direkte Konsequenzen für die Identität des Higgs-Boson-ähnlichen Teilchens, welches im Jahr 2012 am LHC entdeckt wurde.
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Veatch, Jason Robert. "A Search For New Physics Using tt(bar) Resonances in the Lepton Plus Jets Channel at √(s) = 8 TeV in 20 fb⁻¹ of pp Collision Data at the ATLAS Experiment." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/578734.
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Many Beyond Standard Model theories predict particles that couple strongly to top/anti-top quark pairs. This makes tt(bar) a promising signature for new physics searches. The analysis presented in this dissertation uses 20.3 fb⁻¹ of √s = 8 TeV pp collision data from the ATLAS experiment to search for evidence of new physics in the single-lepton plus jets tt(bar) decay channel. This is done by requiring one electron or muon, large missing transverse momentum and additional hadronic jets. The tt(bar) system is reconstructed using techniques optimized for either resolved or boosted event topologies. The results of the analysis are used to set upper limits on the production cross-section times branching ratio for heavy resonances decaying to tt(bar). These limits are interpreted in the context of several benchmark models including the leptophobic topcolor Z', the Randall-Sundrum Kaluza-Klein gluon (gKK), the Randall-Sundrum Kaluza-Klein graviton (GKK) and a spin-0 scalar particle.
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Yap, Yee chinn. "Search for new physics with two photons in the final state with the ATLAS detector." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC005/document.
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Le sujet de cette thèse est la recherche de signaux de physique au-delà du modèle standard,dans le canal de désintégration en deux photons, dans les collisions proton-proton enregistrées par le détecteur ATLAS à des énergies dans le centre de masse de √s = 8 TeV en 2012 et√s = 13 TeV en 2015 et 2016.Une étude de faisabilité de la recherche d’un boson pseudo-scalaire A se désintégrant en un boson Z et un boson de Higgs d’une masse de 125 GeV est présentée. Cette étude est effectuée dans le contexte de modèles prédisant deux doublets de Higgs. L’état final recherché est constitué de deux jets hadroniques et deux photons et les données utilisées sont celles enregistrées en 2012 `a √s = 8 TeV, correspondant `a une luminosité intégrée de 20.3 fb−1. La sensibilité attendue est comparable `a celle atteinte avec une autre recherche effectuée dans la collaboration ATLAS, basée sur l’état final constitué d’une paire d’électrons ou muons et d’une paire de leptons τ . En revanche, elle est inférieure à celle des études dans lesquelles le Higgs est recherché dans sa désintégration en une paire de quarks beaux.La recherche de nouvelles résonances de haute masse se désintégrant en deux photons dans les collisions `a 13 TeV est également présentée. Les échantillons analysés correspondent à des luminosités intégrées de 3.2 fb−1 en 2015 et 12.2 fb−1 en 2016. Deux études sont développées :l’une est optimisée pour la recherche, aussi générale que possible, d’une particule de spin 0; la seconde cible une particule de spin 2 telle que le graviton prédit par le modèle de Randall-Sundrum. Une attention particulière est portée `a la compréhension et la paramétrisation de la forme de la résonance dans l’hypothèse où celle-ci aurait une largeur naturelle non négligeable.L’analyse des données enregistrées en 2015 conclut `a l’observation d’un léger excès autour d’une masse de 750 GeV, d’une largeur d’environ 45 GeV, et dont la significativité statistique locale est estimée à 3,9 et 3,8 écarts standard selon le spin de la résonance recherchée. La significativité globale est estimée à 2,1 écarts standard. L’analyse des données enregistrées en 2016 ne mène à l’observation d’aucun excès significatif. Des limites sur le produit de la section efficace de production d’une résonance par le taux de désintégration en deux photons sont établies : pour une résonance de spin nul, elles vont de 12 fb (51 fb) `a une masse de 200 GeV `a 0,2 fb (0,3 fb)`a 2400 GeV, dans l’hypothèse d’une largeur naturelle de 4 MeV (10% de la masse). Une étude de la reconnaissance des photons se convertissant en une paire électron-positon avant d’interagir avec les calorimètres, basée sur la forme de la gerbe électromagnétique détectée est également documentée. Cette étude a deux objectifs : d’une part, améliorer l’identification des photons convertis dans le contexte de taux d’empilement élevés ; d’autre part, fournir une méthode d’identification basée sur des informations indépendantes (calorimétriques) de celles utilisées par la méthode standard (trajectoires des particules chargées) afin d’évaluer les performances de cette dernièreThis thesis reports on the search for new physics in the diphoton decay channel with the protonprotoncollision data collected by ATLAS at a centre-of-mass energy of √s = 8 TeV in 2012and √s = 13 TeV in 2015 and 2016.A feasibility study of the search for a pseudoscalar A decaying to a Z boson and a 125 GeVHiggs boson in the context of an extended Higgs sector, namedly the two-Higgs-doublet models,is presented. The search is performed with a final state of two jets and two photons using20.3 fb−1 of data at √s = 8 TeV. The expected sensitivity is found to be competitive with theanalysis with a final state of two electrons or muons and two τ leptons, but less sensitive to theother searches with the Higgs decaying to a pair of b-quarks.Search for high mass resonances decaying to two photons at √s = 13 TeV is also presented.The analysed dataset corresponds to an integrated luminosity of 3.2 fb−1 in 2015 and 12.2 fb−1in 2016. Two searches are performed: one optimised for a generic spin-0 particle, and theother for a spin-2 particle using Randall-Sundrum graviton model as benchmark. Particularattention is paid to the understanding and the parameterisation of the line shape of a largewidthresonance. In the search using the collision data recorded in 2015, a moderate excess wasobserved at a diphoton invariant mass around 750 GeV with a best-fit width of around 45 GeV,corresponding to a local significances of 3.8-3.9 standard deviations, depending on the spin ofthe resonance being searched for. The global significances are estimated to be 2.1 standarddeviations. The search is updated with 2016 data and no significant excess is observed. Limitson the production cross-section times branching ratio to two photons for the two resonancetypes are reported: for a spin-0 resonance, the fiducial cross-section ranges from 12 fb (51 fb) at200 GeV to 0.2 fb (0.3 fb) at 2400 GeV, with the narrow (10% of the mass) width hypothesis.A part of this document is also devoted to the study of photons that convert into electronpositronpairs before entering the calorimeter using their electromagnetic shower information.The conversion study has two objectives: improving the identification of photon conversion athigh pile-up rate and providing an orthogonal classification method to assess the performanceof the standard track-based algorithm
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Orovets, Christine M. "Search for Resonant Impurities in Bismuth and Bismuth-Antimony Alloys: Lithium, Magnesium, and Sodium." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337715464.
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Hönig, Georg Friedrich [Verfasser], and Dorothee [Akademischer Betreuer] Schaile. "Search for a scalar dimuon resonance with LHC Run2 data from the ATLAS detector / Georg Friedrich Hönig ; Betreuer: Dorothee Schaile." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2017. http://d-nb.info/1135136351/34.
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Che, Siinn. "Search for long-lived resonance decaying to a dilepton pair in pp collisions at √s = 13 TeV with the ATLAS detector." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534515934683945.
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Lenfeldt, Niklas. "The search for reversibility of idiopathic normal pressure hydrocephalus : aspects on intracranial pressure measurements and advanced MRI techniques in combination with CSF volume alteration /." Umeå : Univ, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1422.
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Abad, David Romero. "Search for massive resonances decaing into pairs of boosted bosons in missing energy plus jet final state Vs=13 TeV." reponame:Repositório Institucional da UFABC, 2017.
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Orientador: Prof. Dr. Eduardo de Moraes GregoresTese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2017.
O Large Hadron Collider (LHC) do CERN foi projetado e construído com o objetivo de proporcionar a observação de fenômenos na fronteira das altas energias. O Compact Muon Solenoide (CMS) é um dos quatros experimentos que observam o resultado das colisões hadrônicas de altas energias geradas pelo LHC, podendo medir com grande precisão diversos parâmetros do Modelo Padrão das interações fundamentais bem como propiciar o descobrimento de novos constituintes da matéria e suas interações. Em sua nova fase de operação, iniciada em junho de 2015 e prevista para durar até 2020, ele vem gerando colisões de prótons a 13 e 14 TeV, propiciando um ambiente de descobertas em regiões do espaço de fase ainda não acessíveis. O objetivo deste trabalho é investigar a possível existência de ressonâncias pesadas que tenham por sinal característico seu decaimento em bósons vetoriais massivos do Modelo Padrão, em particular em um par de bósons vetoriais VZ (V = W, Z). A existência de tais ressonâncias é prevista em muitas extensões do Modelo Padrão, tais como as que preveêm la existência de dimensões extras espaciais ou modelo Simplificados que descrevem novos bósons vetoriais de spin um. Estudaremos o indício da existência de tais ressonâncias analisando os sinais experimentais surgidos quando o bóson V decai em dois jatos hadrônicos e o bóson Z decai invisivelmente em dois neutrinos.
The Large Hadron Collider (LHC) at CERN was designed with the purpose to observe new phenomena on the high energies frontier. The Compact Muon Solenoid (CMS) is one of the four experiments that examine the outcome of hadronic collisions at high energies generated by LHC. It can measure with great accuracy various parameters of the Standard Model of fundamental interactions as well as facilitate the discovery of new constituents of matter and their interactions. In this new stage of operation, initiated in June 2015 and expected to last until 2020, the LHC generates collisions of protons at energies of 13 and 14 TeV, providing an environment of discoveries in regions of phase space still not accessible. The objective of this work is to investigate the existence of heavy resonances which have as characteristic signature, decaying in massive vector bosons of the Standard Model, particularly in a pair of vector bosons VZ (V = W, Z). These kind of resonances are predicted by many extensions of the Standard Model, such as models with extra dimensions or Simplified models that describe new vector bosons of spin one. We will examine the evidence of such resonances by analyzing the experimental signatures that arise when the V boson decays into two jets and the Z boson decays invisibly into two neutrinos.
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Proissl, Manuel Daniel. "Dijet invariant mass studies in the Higgs boson H→bb- resonance search in association with a W/Z boson using the ATLAS detector." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10516.
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The Standard Model of Particle Physics describes the fundamental building blocks of matter and phenomena up to the highest particle interaction energies. The theory demands the existence of a scalar particle: the Higgs boson. The Higgs boson was discovered by the ATLAS and CMS collaborations at CERN using bosonic final states and is measured to have a mass of around 125 GeV. This particle is predicted to decay predominantly into pairs of b-quarks at this mass, but suffers from overwhelming backgrounds from the multijet production expected from QCD interactions. Therefore, H→bb- production in association with a leptonically decaying W or Z boson is considered, with Z → vv-, W → lv and Z → ll, where ` denotes electrons and muons. This thesis presents a search for the Higgs boson decaying into bb- pairs in association with a W or Z boson using the ATLAS detector at the Large Hadron Collider (LHC) at CERN. The analysis uses the full dataset recorded during pp collisions at the LHC in Run-1, corresponding to 4.7 fb-1 at √s = 7 TeV and 20.3 fb-1 at √s = 8 TeV. A multivariate technique and a kinematic cut-based approach have been used to maximize the signal over background ratio, where a particular emphasis on the latter approach is made in this thesis. Final state radiation and reconstruction effects may decrease the bb- resonance resolution significantly, while comparably decreasing the probability of observing the decay over the background. The b quark pairs from the Higgs boson are reconstructed as topological clusters formed to jets in the ATLAS calorimeter. Thus, the reconstruction and calibration of these jets are crucial for the final Higgs mass resolution and paramount for the search and for future precision measurements of V H, H→bb- production. This thesis presents the development and evaluation of advanced techniques to improve the invariant dijet mass reconstruction of the H→bb- candidate. Sequential jet calibrations, semileptonic corrections and pT corrections to account for the interplay between jet resolution/scale and the underlying signal pT spectrum obtained from Monte Carlo simulations have been studied. A major focus has been made on the development and evaluation of an event-level kinematic likelihood fitting framework to exploit the full kinematic potential of V H topologies within the detector uncertainties of the reconstructed final state signatures in order to improve the measurement of the b-tagged jet kinematics. The jet energy calibrations of the H→bb- signal candidates yield an overall improvement of the dijet invariant mass resolution of up to ~30%, and of the expected statistical significance of ~12%. The analysis procedure is validated using the resonant V Z(bb-) production in the same final states as for the Higgs boson search, and is observed, compatible with the Standard Model expectation, with a significance of 4.9 standard deviations and a signal strength of μ^V Z = 0:74+0:17 -0:16. For a Higgs boson mass of 125.36 GeV, the observed (expected) deviation from the background-only hypothesis is found with a significance of 1.4 (2.6) standard deviations and a signal strength is determined to be μ^V H = 0:52±0:32(stat.)±0:24(syst.).
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Hönle, Andreas [Verfasser], Hubert [Akademischer Betreuer] Kroha, Hubert [Gutachter] Kroha, and Lothar [Gutachter] Oberauer. "Searches for new resonances decaying to a Higgs and a vector boson with the ATLAS detector at the LHC / Andreas Hönle ; Gutachter: Hubert Kroha, Lothar Oberauer ; Betreuer: Hubert Kroha." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1239240120/34.
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Barnovska, Zuzana. "Diphoton measurements with the ATLAS detector at LHC : search for new resonances and study of diphoton production in association with jets." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY072/document.
Full textAbstract:
Cette thèse étudie les collisions pp à sqrt{s} = 8 TeV avec des paires de photons dans l'état final, telles que recueillies par l'expérience ATLAS au LHC au cours de 2012. L'état final avec diphoton s'est avéré cruciale pour la découverte du boson de Higgs. La motivation pour la recherche de résonances supplémentaires se désintégrant en deux photons est très forte en raison l'existence de nombreux modèles prévoyant un secteur de Higgs étendu. Dans le même temps, des mesures détaillées des sections efficaces diphoton sont nécessaires pour établir la précision des prédictions théoriques actuellement disponibles pour ces processus.La mesure des photons par ATLAS repose sur un excellent étalonnage de la réponse du calorimètre électromagnétique. Pour cette raison, les études liées à l'étalonnage de la réponse de photons dans le calorimètre Argon Liquide (LAr) sont initialement réalisées, y compris la mesure de l'étalonnage par rapport à l'échelle de l'énergie de la couche calorimètre utilisant des photons, et la nécessité éventuelle d'un inter-étalonnage de la réponse en énergie des photons en fonction de l'angle azimutal $phi$. Une étude de l'amplitude du bruit du calorimètre dans des conditions de pile-up élevés est également présentée, aboutissant à des recommandations pour les configurations d'échantillonnage d'impulsion LAr au Run2.La recherche d'une résonance supplémentaire se désintégrant en deux photons est effectuée et aucun signal n'est observé: une limite est mise sur la section efficace fiducielle d'une résonance multipliée par son rapport de branchement de désintégration en diphoton. La mesure de la section efficace de production de diphoton isolés en association avec des jets est effectuée en fonction de la masse invariante de diphoton, l'impulsion transverse du système diphoton, la différence d'angles dans le plan azimutal de l'angle entre les deux photons et l'angle theta de coplanarité, en fonction de la multiplicité en jets et de différentes variables associés aux jets. Les résultats sont comparés aux dernières prévisions QCD Next-To-Leading-Order QCD. Une telle mesure est la première du genre effectuée au LHCThis thesis studies pp collisions at sqrt{s}=8 TeV with pairs of photons in the final state, as collected by the ATLAS experiment at the LHC during 2012. The diphoton final state has proven to be crucial to the discovery of the Higgs boson. The motivation for searching for additional resonances decaying into two photons is very strong due to many models predicting an extended Higgs sector. At the same time, detailed measurements of diphoton cross sections are necessary to establish the quality of the theoretical predictions currently available for these processes.The measurement of photons by ATLAS relies on an excellent calibration of the electromagnetic calorimeter response. For this reason, studies related to the calibration of the photon response in the ATLAS Liquid Argon (LAr) calorimeter are initially performed, including a measurement of the calorimeter layer energy scale relative calibration using photons, and the potential need of an inter-calibration of the photon energy response as a function of the azimuthal angle $phi$. A study of noise performance of the calorimeter in high pile-up conditions is also presented, resulting in recommendations for the LAr pulse sampling configurations for Run2.A search for an additional resonance decaying into two photons is performed, leading to no significant excess being observed. A limit on the fiducial cross section times branching fraction of a new resonance decaying into two photons is therefore computed. The measurement of the production cross section of isolated prompt diphoton in association with jets is performed as a function of the diphoton invariant mass, the transverse momentum of the diphoton system, the azimuthal angle difference of the two photons and the coplanarity angle theta, for jet multiplicity categories and as a function of various jet variables. The results are compared to the latest Next-To-Leading-Order QCD predictions. Such a measurement has not been previously published at the LHC