Дисертації з теми "Associated Bottom Higgs Production"
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Dovier, Giacomo Oliviero. "Semi-inclusive associated bottom-Higgs production at LHC: the complete one-loop electroweak in the MSSM." Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4815.
Повний текст джерелаIl bosone di Higgs il tassello mancante del Modello Standard: predetto da Peter Higgs negli anni sessanta, non ancora stato osservato sperimental- mente. Il Large Hadron Collider stato costruito con questo obiettivo in mente, assieme a molti altri. Uno dei processi pi interessanti per la pro- duzione di Higgs Supersimmetrico bg -> bH0 ( A0, h0). La natura dell'accoppiamento Yukawa nel MSSM lo rende predominate per alti valori di tan(beta) . In questa tesi vengono calcolate le correzioni elettrodeboli ad un loop alla sezione d'urto del processo nel MSSM, e viene mostrato come esse possano essere molto rilevanti per alcune regioni dello spazio dei parametri. Viene anche mostrato come i risultati siano indipendenti dalla scelta dello schema di rinormalizzazione tra DCPR and DR, ed anche come la consueta Improved Born Approximation non riproduca accuratamente i risultati ad un loop, mentre una diversa possibile approssimazione, la Reduced Vertex Approximation, in migliore accordo con il calcolo completo. Viene quindi eff ettuato un confronto con i risultati per un Two Higgs Doublet Modle, e viene mostrato come la di erenza con i risultati nel MSSM sia rilevante ad un loop, rendendo lo studio di questo processo una possibile via per discriminare tra i due modelli.
The Higgs particle is the missing piece of the Standard Model picture: pre- dicted by Peter Higgs in the late sixties, it has yet to be observed in a collider. The Large Hadron Collider has been built with this goal in mind, among many others. A very important channel to look at for SUSY Higgs production is bg -> bH0 (A0, h0). The nature of the MSSM Yukawa couplings make it dominant for high Values of tan(beta) . In my work I calculate the electroweak one loop corrections to the cross section of the process' cross section in the MSSM, and show that they can be very relevant for some regions of the parameters' space. It is also shown how the results obey a nice scheme independence at one loop for the two renormalization schemes DCPR and DR, as well as how the usual Improved Born Approximation fails in this case to reproduce the one loop results accurately, while a di fferent suggested Reduced Vertex Approximation is in better agreement with the full calculation. I then proceed to make a comparison with the results for a Two Higgs Doublets Model, and show that the di fference with the MSSM are big at the one loop level, such that this process could provide a way to discriminate between the two models.
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Lund, Gustav. "Associated charged Higgs boson and squark production in the NUHM model." Thesis, Uppsala University, High Energy Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-114395.
Повний текст джерелаConventional searches for the charged Higgs boson using its production in association with Standard Model (SM) quarks is notoriously weak in the mid-tanB range. Hoping to find an alternate channel to fill this gap, the production of the charged Higgs boson in association with supersymmetric squarks is studied. Using Monte Carlo generators the production at the LHC is simulated within the non universal Higgs mass model (NUHM). If the six parameters of the model (m0, m1/2, A0, tanB, u, mA) induce small masses of the stop, sbottom and charged Higgs, the production cross section can be of the order pb. Through scans of the input parameter the cross section is maximized, with the requirement that the stop decays directly to a neutralino - simplifying detection, in the point (m0, m1/2, A0, tanB, u, mA) = (190, 187, -1147, 179, 745, 13.2) where the cross section is 559 fb.
The production is compared to the irreducible backgrounds stop, stop, t, tbar and t, tbar + 2 jets. The former poses no severe constraints and can be easily removed using appropriate cuts. The latter, SM background, has a cross section almost 1000 times larger and strong cuts must be imposed to suppress it. Neglecting hadronization and systematic effects, we show that a 5 sigma discovery is possible at 133 fb-1. In this range, mH+ = 194 GeV and tanB = 13.2, other channels have little or no prospects of detecting the charged Higgs and the studied process shows good prospects for complementing charged Higgs searches at the LHC in the mid-tanB range.
Agaras, Merve Nazlim. "Searches for associated Higgs Boson production with top quark pair and Higgs pair production in multi lepton final states with the ATLAS detector." Thesis, Université Clermont Auvergne (2017-2020), 2020. http://www.theses.fr/2020CLFAC023.
Повний текст джерелаSince the discovery of the Higgs boson at a mass around 125 GeV by both ATLAS and CMS collaborations in July 2012, it became crucial to measure its properties, such as its couplings to other particles, and search for any deviations from the Standard Model (SM) predictions. The top quark Yukawa coupling is close to unity and the strongest in the fermionic sector. Therefore, this coupling plays a crucial role in the theory. Determination of the associated production of The Higgs boson production with a pair of top quarks (ttH) offers a tree-level access to measuring this coupling. The analysis of ttH production at ATLAS experiment exploits several Higgs decay channel, together with different top quark decay modes. In this thesis, the study of the ttH (H → Multi lepton) process is presented in the topology where the Higgs decays to WW,ZZ or tautau, using a dataset corresponding to an integrated luminosity of 79.8fb^-1 at √s = 13 TeV, collected with the ATLAS detector between 2015-2017. Improved knowledge on the background modelling and the complex fit model is used with many degrees of freedoms. Particularly different fit setups are presented in order to understand the modelling of the major irreducible background, ttW. Furthermore, a search for the SM Higgs boson pair production in the multi lepton final states is presented. The search uses 139fb^-1 of proton-proton collisions data at a centre-of-mass energy of 13 TeV provided by the Large Hadron Collider (LHC) and recorded by the ATLAS experiment in 2015 and 2018. The first studies in two lepton same-sign channel is performed for lepton working point optimisation and estimation of background contributions. Template fit method is applied to estimated the reducible backgrounds and preliminary expected upper limit is calculated
Agnew, James Paul. "Search for the associated production of Higgs boson with top anti-top pairs." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/search-for-the-associated-production-of-higgs-boson-with-top-antitop-pairs(c24f5919-6f3f-4b13-ad72-9ef9efbcb6bb).html.
Повний текст джерелаBlack, Curtis William. "Search for the Higgs boson decaying to tau leptons in the associated production mode at ATLAS." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/15432.
Повний текст джерелаCIRIOLO, VINCENZO. "Study of the Higgs boson associated production with a vector boson in the Higgs boson diphoton decay channel with the CMS detector." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241085.
Повний текст джерелаThis Ph.D. thesis presents a study of the associated production of the Higgs boson with a vector boson (VH) in proton-proton collisions, using data collected at a center-of-mass energy of 13 TeV with the CMS experiment in 2016 for an integrated luminosity of 35.9 fb −1 . The study is restricted to final states were the Higgs boson decays in two photons (H→ γγ). After an introduction on the experimental and theoretical landscape that motivates this study (Chapter 1) and an overview of the CMS experiment (Chapter 2), the exper- imental work performed to ensure the best quality of the CMS ECAL reconstruction is described in detail (Chapter 3). The analysis method and the results are then described (Chapter 4), including the discussion of optimization steps that were identified and will be relevant for future developments. In particular, the channels with the vector boson decaying into a pair of quarks and the W boson decaying into a lepton and a neutrino are described This analysis, included in a paper recently submitted for publication, represents the first result on the measurement of the VH production process in the H→ γγ final state with the LHC Run 2 data.
Howard, Jacob Russell. "Measurements of the Higgs Boson in the H-ττ decay channel". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:14e6e708-0cd6-4022-a4b2-343c18c8e260.
Повний текст джерелаWalser, Manuel. "NLO QCD and SUSY-QCD corrections to associated MSSM Higgs production with heavy quarks at hadron colliders /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17592.
Повний текст джерелаAsquith, L. "Using ATLAS to investigate the associated production of a Higgs Boson with a pair of top quarks." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20202/.
Повний текст джерелаTenaglia, Giovanni. "Performance studies of the CMS distributed analysis system in the associated Higgs boson production with top quarks." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7704/.
Повний текст джерелаRoberts, Rhys. "Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/evidence-for-the-associated-production-of-the-higgs-boson-and-a-top-quark-pair-with-the-atlas-detector(ae9de2a2-b533-41db-9eb7-b25ac77afcdf).html.
Повний текст джерелаWang, Chao. "Search for the production of the Higgs boson associated with a pair of top quarks with the Atlas detector at the LHC." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0433/document.
Повний текст джерелаThe production of the Higgs boson associated with a pair of top quarks is one of the most important Higgs boson production modes yet still not observed. Therefore, its discovery is one of the most challenging searches after the Higgs discovery: not only will it be the first time we can observe this Higgs production mode but also we will be able to measure its Yukawa coupling to the top quark. The measured results can answer the basic question of the Standard Model (SM) and can also search for any hints of new physics beyond the SM prediction. An analysis searching for the production of the Higgs boson associated with a pair of top quarks in three leptons final states is presented in this thesis. It is performed with the data collected by the ATLAS detector in 2015 and 2016 during the so-called « Run 2 » campaign corresponding to an integrated luminosity of 36.1 fb−1 at a center of mass energy of 13 TeV. It uses a boosted decision tree algorithm to discriminate between signal and background. The dominant background of fake leptons is estimated with the data-driven matrix method (Matrix Method). For a 125 GeV Standard Model Higgs boson, an excess of events over the expected background from other SM processes is found with an observed significance of 2.2 standard deviations, compared to an expectation of 1.5 standard deviations. The best fit for the $t\bar tH$ production cross section is $1.5^{+0.8}_{-0.7}$ times the SM expectation, consistent with the SM value of the Yukawa coupling to top quarks
Parks, Brandon Scott. "Search for the Higgs Boson in the ZH → vvbb̄ Channel at CDF Run II." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1215108702.
Повний текст джерелаHäfliger, Petra. "Associated MSSM Higgs production with heavy quarks : SUSY-QCD corrections & impact of Ao on the mSUGRA parameter space /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16970.
Повний текст джерелаWarsinsky, Markus. "Studies of b-associated production and muonic decays of neutral Higgs bosons at the ATLAS experiment within the Minimal Supersymmetric Standard Model." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1221746748987-12927.
Повний текст джерелаDie vorliegende Arbeit präsentiert eine Monte Carlo Studie zu neutralen Higgs-Bosonen des Minimal Supersymmetrischen Standardmodells (MSSM) im myonischen Zerfallskanal am Atlas Experiment am Large Hadron Collider des CERN. Signal- und Untergrundprozesse werden mit neuartigen Monte Carlo Ereignisgeneratoren simuliert, die Teile der Korrekturen höherer Ordnung beinhalten, und von denen eine verbesserte Vorhersage erwartet wird im Vergleich zu herkömmlichen Programmen. Der SHERPA Monte Carlo Ereignisgenerator wird auf seine Brauchbarkeit für die Analyse überprüft und mit Ergebnissen anderer Programme verglichen. Sofern möglich werden die erstellten Monte Carlo Datensätze mittels Rechnungen zu höheren Ordnungen normiert. Um eine hinreichend große Statistik von simulierten Daten zu erhalten, wird die schnelle Detektorsimulation des ATLAS Detektors ATLFAST verwendet. Unterschiede zwischen der vollständigen Detektorsimulation und ATLFAST werden untersucht, und sofern möglich, Korrekturverfahren entwickelt. Eine schnittbasierte Analyse wird durchgeführt unter der Annahme einer integrierten Luminosität von 30 inversen femtobarn und optimiert mit Hinblick auf das Entdeckungspotenzial für MSSM Higgs-Bosonen. Die systematischen Unsicherheiten der Ereignisauswahl und der Monte Carlo-Vorhersagen werden abgeschätzt. Eine Methode zur Messung des Untergrundes in Daten wird vorgestellt und überprüft. Schliesslich wird das Entdeckungspotenzial des ATLAS Experiments in Vergleichspunkten für CP erhaltende Szenarien des MSSM ermittelt. F\ür niedrige Massen des pseudoskalaren Higgs-Bosons A kann mindestens eines der neutralen Higgs-Bosonen des MSSM im myonischen Zerfallskanal entdeckt werden, sofern der Modellparameter tan(beta) mindestens 20 ist. Für hohe Massen des A muss ein wesentlich größeres tan(beta) in der Natur realisiert sein, um eine Entdeckung im untersuchten Zerfallskanal zu ermöglichen. Die Sensitivität von ATLAS auf Higgs-Bosonen des MSSM ist um ein Vielfaches höher als diejenige bisheriger oder momentan laufender Experimente
Hohn, David [Verfasser]. "Search for top-quark-pair associated Higgs production with tau leptons using the ATLAS detector at the LHC / David Hohn." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1185576126/34.
Повний текст джерелаShaw, Christian Alexander. "Standard model Higgs boson analysis via associated top production and hadronic decay using the ATLAS detector at the CERN LHC." Thesis, University of Glasgow, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443421.
Повний текст джерелаTonon, Nicolas. "Search for the associated production of a single top quark and a Z or Higgs boson with the CMS experiment." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE022.
Повний текст джерелаThis thesis presents 4 different studies based on the data collected by CMS during the Run 2 of the LHC. Firstly, a search for the production of a single top quark and a Z boson (tZq) is conducted. This rare process probes Standard Model couplings, and may be sensitive to new physics processes. This search targets the trilepton final state and resulted in an evidence for the tZq process. A second analysis targets the production of a single top quark and a Higgs boson (tH) in multileptonfinal states. It is the only process sensitive at LO to the sign of the top quark Yukawa coupling. Constraints are placed on the value of the top quark Yukawa, and on the tH cross section. In addition, the analysis is re-adapted to search for FCNC processes with similar final states. Finally, a study of the ageing due to irradiation of the strip tracker is presented
Li, Changqiao. "b-tagging calibration and observation of Higgs boson decays to a pair of bottom quarks with the atlas detector." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS620.
Повний текст джерелаThis thesis firstly describes a measurement of the b-jet tagging efficiency with a tag-and-probe method using data recorded by the ATLAS detector in 2015 and 2016. The efficiency measurement method, the object selection, the event and probe jet selection, the evaluation of the statistical and systematic uncertainties, and the final results are discussed. The b-tagging efficiencies have been measured as a function of the jet transverse momentum, pseudorapidity and of the average number of pile-up collisions. The efficiencies measured in data have been compared to those predicted from simulation, and simulation-to-data efficiency scale factors have been determined. The efficiency scale factors are close to unity, with total uncertainty ranging between 2% and 12%. The second part of this thesis focuses on the search for the decays of the Standard Model (SM) Higgs boson to bottom quarks in the associated production mode with vector bosons. Two measurements have been performed and are described here: the first one is based on of 13 TeV pp collisions recorded by ATLAS during the LHC Run-2 until 2016; the second one includes the additional of 13 TeV pp collisions recorded in 2017. For the study based on of data, the object reconstruction, event selection and classification, the techniques to discriminate the signal from the background, the main background and their modelling, the signal properties and the interpretation of results are discussed. For the study based on data, the main difference from the previous study are highlighted. Both results provide a strong evidence of the process, with statistical significances of 3.5 and 4.9 standard deviations, respectively. The signal strength, defined as the ratio between the measured cross section times branching ratio and the SM prediction, is measured with the 2015–2017 dataset to be , indicating good agreement with the SM. The combination of the results based on of 13 TeV collisions with the results of the same analysis performed on data collected at lower (7 and 8 TeV) centre-of-mass energies in 2011 and 2012, and witht those of the searches of decays in other Higgs boson production modes (vector-boson fusion, associated production with a top-quark pair) have led to the observation of the decay with a significance of 5.4 standard deviations, and to a measurement of the signal strength . A combination of the results of the results based on of 13 TeV collisions with the results of searches for the same production mode on the same amount of data in the diphoton and ZZ∗ → 4l Higgs boson final states has led to the observation of VH production with a significance of 5.3 standard deviations, and to a measurement of the signal strength , in good agreement with the SM
Asbah, Nedaa Alexandra. "Search for the Production of a Standard Model Higgs Boson in Association with Top-Quarks and Decaying into a Pair of Bottom-Quarks with 13 TeV ATLAS Data." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19311.
Повний текст джерелаThis thesis presents the search for the Standard Model Higgs boson produced in association with a pair of top-quarks (ttH). The analysis uses a 36.1 1/fb dataset of proton-proton collisions collected with the ATLAS detector, at the Large Hadron Collider during 2015 and 2016. The selected events contain either one or two leptons from the decay of the top-quark pair. In order to improve the sensitivity of the search, events are split in regions according to the number of jets and how likely these events are to contain b-jets. Methods based on multivariate techniques were developed and applied in the signal-enriched regions to discriminate ttH events against background events being dominated by top pair production with additional b-jets. All analysis regions are combined in a statistical model using a profile likelihood fit to constrain the background predictions and reduce the systematic uncertainties. An excess of events over the expected Standard Model background is found with an observed (expected) significance of 1.4 (1.6) standard deviations. A ttH signal strength larger than 2.0 is excluded at the 95% confidence level.
Slaunwhite, Jason M. "Search for the Higgs Boson Produced in Association with a W Boson at CDF Run II." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1232121462.
Повний текст джерелаNechansky, Filip. "Search for the production of a Higgs boson decaying into a pair of bottom quarks in association with a pair of top quarks at 13 TeV with the ATLAS detector." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/23027.
Повний текст джерелаThe discovery of the Higgs Boson in 2012 confirms the Standard Model as the most successful theory describing the fundamental interactions of elemental particles. One of the important properties of the Higgs boson is its Yukawa coupling to the top quark, which in the Standard Model is the strongest due to the high mass of the quark. This thesis reports on a measurement of the top-Yukawa coupling with data collected by the ATLAS detector from 2015 to 2018 at 13 TeV center of mass energy. The coupling is studied in ttH(bb) events, a final state containing decay products of two top quarks with additional emission of a Higgs boson, where the Higgs decays into a pair of bottom quarks. This decay channel of the Higgs Boson has the largest branching ratio, but is systematically limited by the description of the dominant background process ttbb, a tt with additional two b quarks in the final state. The measurement takes advantage of the ability of the ATLAS detector to identify jets coming from a b quarks to construct analysis regions with various compositions of the signal and the background. To further separate the signal, a series of multivariate algorithms is employed and the ttH process is then extracted using a profile likelihood fit. The results are shown for the channel with a single lepton in the final state and for a combination with the dilepton channel. The background performance is studied in detail, where large mis-modeling is found. The measured ratio of the ttH production compared to the Standard Model prediction is found to be mu(ttH) = 0.84 +0.45 -0.39 (syst.) +-0.21 (stat.). The result is in agreement with the Standard Model prediction and corresponds to an observed (expected) significance of 1.9 sigma (2.3 sigma), an improvement compared to the previous ATLAS measurement which reported 1.4 sigma (1.6 sigma).
Yang, Xuan. "Mesure de la production du boson de Higgs standard en association avec une paire de quarks top et antitop et recherche d'un boson de Higgs chargé se désintégrant en une paire de quarks top et bottom à l'aide du détecteur ATLAS au LHC." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY015.
Повний текст джерелаThe Higgs field plays an important role in the Standard Model (SM). It is not only responsible for elementary particles generation but also the only scalar field in the SM. Hence study of the Higgs boson becomes one of the most popular topics at LHC. It provides a great opportunity to probe the SM predictions and search for beyond SM evidence. New physics beyond the SM usually has a more complicated Higgs scenario and predict more than one Higgs boson, such as a charged Higgs boson. Searching for these new particles will give us a direct hint of new physics.In this thesis, two main contributions are presented, searching for a heavy charged Higgs boson (H +) decaying to t t H and searching for H + production in multilepton final states. The search for H + is performed with data collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1. There is no significant excess of H + signal over the SM backgrounds observed in the mass range from 200 GeV to 2000 GeV. The largest deviation from the SM hypothesis obtained from the fit is observed at 300 GeV, corresponding to a local p0 de 1,13%. The search for t t H prodcution in multilepton final state is performed with data collected during 2015-2017, corresponding to an integrated luminosity of 79.9 fb-1. The Yukawa coupling of the Higgs boson and top quark can be directly determined from the measurement of t t H production cross section. This analysis aims at observation of t t H production using only multilepton final states. There are six final states defined by the number of light leptons (electrons or muons) and hadronic taus, and 25 event categories to search for t t H signal and estimate fake leptons simultaneously. The studies in the final state with two same-sign leptons and one hadronic tau is discussed in detail. An excess of t t H events over other SM backgrounds is found with an observed (expected) significance of 1,8 σ (3,1 σ). The measured t t H production cross section is 294 (+ 182 / -162) fb, which is consistent with the SM prediction
BESCHI, ANDREA. "Measurement of the associated production of top quark pairs with a Higgs boson in the diphoton final state with the CMS detector." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/261931.
Повний текст джерелаThis thesis presents the analysis of the data collected in 2016 and in 2017 by the CMS detector at the Large Hadron Collider to perform a precise measurement of the cross section of the Higgs boson production in association with a pair of top-antitop quarks (ttH). The diphoton decay channel of the Higgs boson is exploited to perform the measurement, as among the most sensitive channels. The analysis exploits 35.9 fb−1 of data collected in 2016 and 41.5 fb−1 collected in 2017 in proton-proton collisions at a centre-of-mass energy of 13 TeV. At the beginning of this work, the measured cross section of the ttH process showed a mild departure from the standard model (SM) expectation of about two standard deviations. A more precise determination was necessary to ascertain whether the observed tension was due to a statistical fluctuation or to some unpredicted feature. The choice of the diphoton decay channel is due to the fully reconstructed final state and to the low number of events arising from different processes but with similar topology, namely background. The experimental signature of a Higgs boson decaying to a pair of photons is the presence of a narrow resonant peak arising in the invariant mass distribution of the photon pairs. The ttH production can be exclusively identified by the presence in the final state of the decay products of the top quarks. The ttH production rate is extracted from a fit to the invariant mass spectrum of the photon pairs. The fit function is based on a signal model, built from simulation of the Higgs boson production processes, and a background one, derived directly from fitting the data.The fit is performed with floating the signal strength μ, defined as the ratio between the measured ttH production cross section and the SM expectation. The analysis of the 2016 data resulted in an observed value of μ = 2.2+0.9−0.8, rejecting the background-only hypothesis at 3.2 standard deviations, where 1.5 is expected for a SM Higgs boson. The refinement of the techniques exploited for the data analysis lead to an improvement in the sensitivity of more than 50 % in the analysis of the 2017 data, with μ = 1.3+0.7−0.5, rejecting the background-only hypothesis at 3.1 standard deviations, where 2.2 are expected for a SM Higgs boson. The combination of the two analyses resulted in an observed signal strength of μ = 1.7+0.6-0.5, corresponding to a significance of 4.1 standard deviations. The analysis of the 2016 data, together with the analyses targeting final states with the Higgs boson decaying in b quarks, vector bosons and τ leptons, allowed the first experimental observation of the ttH process. The result exploited the analysis of the data collected in 2016 at a centre-of-mass energy of 13 TeV, as well as the data collected in 2011 and 2012 at a centre-of-mass energy of 7 and 8 TeV, respectively. The best fit value of the combination of the different channels is μ = 1.26+0.31−0.26, in agreement with the SM expectation. The background-only hypothesis is rejected at the level of 5.1 standard deviations. This result proves for the first the tree-level coupling of the Higgs boson with the top quarks and, hence, with an up-type quark.
Bryant, Patrick. "Search for Pair Production of Higgs Bosons in the Four Bottom Quark Final State Using Proton-Proton Collisions at √S = 13 Tev with the ATLAS Detector." Thesis, The University of Chicago, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10974446.
Повний текст джерелаA search for Higgs boson pair production in the four b-jet final state is carried out with up to 36.1/fb of LHC proton--proton collision data collected at √s = 13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. This thesis presents a search in events with four individually resolved b-tagged jets. Higgs bosons produced with large momenta are reconstructed as single large radius jets with substructure. The analysis of this topology is presented in CERN-THESIS-2018-118. The two analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to four b-quarks are set in each model. The combined result searches for resonance masses in the range 260–3000 GeV. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.
Ma, Yanhui. "Observation du mode de désintégration H→bb et de la production associée de VH avec le détecteur ATLAS." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS099/document.
Повний текст джерелаA search for the Standard Model Higgs boson produced in association with a W or Z boson, and decaying to a bb pair has been performed with ATLAS detector. The data were collected in proton-proton collisions during Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 79.8 fb⁻¹. Three channels containing zero, one and two charged leptons (electrons or muons) have been considered to target each of the leptonic decays of the W or Z boson, Z->vv, W->lv et Z->ll, referred to as as the 0-lepton, 1-lepton and 2-lepton channels, respectively. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 4.9 standard deviations, compared to an expectation of 4.3 standard deviations. The ratio of the measured signal events to the Standard Model expectation equal 1.16 +0.27/-0.25 = 1.16 +/-0.16(stat) +0.21/-0.19(syst). The result is also combined with the other results from the searches for the Higgs boson in the bb 18 decay mode in Run 1 and Run 2, the combination yields an observed (expected) significance of 5.4 (5.5) 20 standard deviations, and therefore provides a direct observation of the Higgs boson decay into a bb pair. In addition, a combination of Run 2 results searching for the Higgs boson produced in association with a W or Z boson yields an observed (expected) significance of 5.3 (4.8) standard deviations, and therefore provides a direct observation of Higgs boson being produced in association with a W or Z boson
Gargiulo, Simona [Verfasser], and Christian [Akademischer Betreuer] Weiser. "Measurement of the Higgs boson decay to a pair of b-quarks in the associated production with a vector boson with the ATLAS detector." Freiburg : Universität, 2021. http://d-nb.info/1236550706/34.
Повний текст джерелаBiondi, Silvia <1990>. "Study of the Associated Production of the Higgs Boson with a Top Quark Pair in a Boosted Regime in the ATLAS Experiment at LHC." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/7811/1/Biondi_Silvia_tesi.pdf.
Повний текст джерелаIn questa tesi è presentata la misura della “signal strength” (μ = σ obs/σ ttH SM ) e del limite superiore della produzione associata di un bosone Higgs con una coppia di quark top, pp → ttH + X ad un’energia del centro di massa di 13 TeV. I dati sono stati acquisiti dall’esperimento ATLAS nel 2015 e 2016, corrispondenti ad una luminosità integrata di 36.5 fb^(-1). La signal strength del canale ttH e il suo limite sono stati misurati studiando i canali di decadimento H → bb e tt→ lνbqq ̄ b, con due differenti approcci. Nel primo (detto “resolved”), sono stati usati gli algoritmi standard di identificazione e ricostruzione come nelle precedenti analisi già pubblicate. Nel secondo (detto “combined”), gli eventi sono separati in due regimi esclusivi, includendo quelli contenenti il quark top adronico con un basso momento trasverso (pT < 250 GeV) e quelli boosted con la richiesta opposta, dove i jet parzialmente sovrapposti provenienti da top con alto pT vengono ricostruiti e identificati con metodi innovativi. Il campione di eventi boosted è sensibile ad una regione cinematica significativamente differente e, per questo, fornisce informazioni aggiuntive. La signal strength misurata è 1.4±0.5 e 1.2±0.5 rispettivamente per l’analisi resolved e combined. Una signal strength più grande di 2.3 e 2.0 può essere esclusa con un livello di confidenza del 95%, rispettivamente per l’analisi resolved e combined. Entrambi i risultati sono compatibili con la previsione del Modello Standard (μ = 1).
Rieger, Marcel [Verfasser], Hans Martin [Akademischer Betreuer] Erdmann, and Alexander [Akademischer Betreuer] Schmidt. "Search for Higgs boson production in association with top quarks and decaying into bottom quarks using deep learning techniques with the CMS experiment / Marcel Rieger ; Hans Martin Erdmann, Alexander Schmidt." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/119571503X/34.
Повний текст джерелаBrown, Jonathan. "Search for WH associated production in the lνbb final state using the DØ detector at the Tevatron". Phd thesis, Université Paris-Diderot - Paris VII, 2011. http://tel.archives-ouvertes.fr/tel-00918068.
Повний текст джерелаNoguchi, Yohei. "Measurement of Higgs boson properties using the decay channel to b-quarks following associated production with a vector boson in pp collisions at √s=13 TeV." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263460.
Повний текст джерелаFink, Simon [Verfasser], and Th [Akademischer Betreuer] Müller. "Probing the Top-Yukawa Coupling by Searching for Associated Higgs Boson Production with a Single Top Quark at the CMS Experiment / Simon Fink. Betreuer: Th. Müller." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1110969635/34.
Повний текст джерелаDavis, Kevin Patrick. "Measurement of the bottom quark production cross section in proton-antiproton collisions at a center-of-mass energy 630 GeV using muons with associated jets." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284341.
Повний текст джерелаy
< 1 using a sample of muons with associated jets collected with the D⊘ detector in pp̄ collisions at √s = 630 GeV at the Fermilab Tevatron. The measured b-quark cross section is consistent in shape with O(α³s) QCD predictions, but exceeds them in normalization by roughly a factor of 2.5.
Nechansky, Filip [Verfasser]. "Search for the production of a Higgs boson decaying into a pair of bottom quarks in association with a pair of top quarks at 13 TeV with the ATLAS detector / Filip Nechansky." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1236896971/34.
Повний текст джерелаHageböck, Stephan [Verfasser]. "Search for the H -> bb Decay of the Standard Model Higgs Boson in Associated Production with Vector Bosons Using ATLAS Data at s = 8 TeV / Stephan Hageböck." Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1173789545/34.
Повний текст джерелаBokan, Petar [Verfasser]. "Pair production of Higgs bosons in the final state with bottom quarks and τ leptons in the ATLAS experiment: Search results using LHC Run 2 data and prospect studies at the HL-LHC / Petar Bokan". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://d-nb.info/1230824421/34.
Повний текст джерелаAsbah, Nedaa Alexandra [Verfasser], Judith [Gutachter] Katzy, Thomas [Gutachter] Lohse, and Hannes [Gutachter] Jung. "Search for the Production of a Standard Model Higgs Boson in Association with Top-Quarks and Decaying into a Pair of Bottom-Quarks with 13 TeV ATLAS Data / Nedaa Alexandra Asbah ; Gutachter: Judith Katzy, Thomas Lohse, Hannes Jung." Berlin : Humboldt-Universität zu Berlin, 2018. http://d-nb.info/1185666214/34.
Повний текст джерелаTherhaag, Jan [Verfasser]. "Search for the H→bb decay mode of the Standard Model Higgs boson in associated production with a vector boson in proton-proton collisions at √s=8TeV with the ATLAS experiment / Jan Therhaag." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1054691649/34.
Повний текст джерелаMaier, Benedikt [Verfasser], and Th [Akademischer Betreuer] Müller. "Search for the associated production of a single top quark and a Higgs boson in the H to bbbar decay channel at 8 and 13 TeV with the CMS experiment / Benedikt Maier. Betreuer: Th. Müller." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/109943243X/34.
Повний текст джерелаPogorelov, Yury. "A search for the associated Higgs production in the Tau channel." 2007. http://etd.nd.edu/ETD-db/theses/available/etd-07192007-233028/.
Повний текст джерелаThesis directed by Anna Goussiou and Randal Ruchti for the Department of Physics. "July 2007." Includes bibliographical references (leaves 126-128).
Hofmann, Franziska [Verfasser]. "Influence of the supersymmetric bottom sector on higgs production and decay / vorgelegt von Franziska Hofmann." 2009. http://d-nb.info/996637427/34.
Повний текст джерелаKok-Wee, Song. "Associated Production of The Light Pseudoscalar Higgs Boson with Chargino pair in NMSSM." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0016-0109200613413706.
Повний текст джерелаSong, Kok-Wee, and 宋國維. "Associated Production of The Light Pseudoscalar Higgs Boson with Chargino pair in NMSSM." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/73290707511687468766.
Повний текст джерела國立清華大學
物理學系
94
Supersymmetry is the symmetry between fermion and boson and this symmetry is very useful. Supersymmetry have many applications in physics, sometime it can solve some of the difficult problem. Minimal Supersymmetric Standard Model (MSSM) is the model which is minimally embedding super- symmetry into Standard Model. MSSM has several advantages, especially it give a solution to the hierarchy problem. Although this model is very attractive, MSSM has its own difficulty, it is “μ-problem”. This difficulty can be removed by introducing a new singlet scalar Higgs field and extended MSSM to the model call Next-to-Minimal Supersymmetry Standard Model. The NMSSM has an additional new pseudoscalar singlet Higgs and a new singlino in contrast to the MSSM. This model has some modification of the property of pseudoscalar Higgs boson. First, NMSSM give another new pseudoscalar Higgs into the theory which could be very light even less than a GeV, but in MSSM the pseudoscalar Higgs is very haevy (always a few hundred GeV). Secondly, even the gauge singlet property of this pseudoscalar Higgs, but it still posses a non-zero coupling to the charginos, neutralinos as well as the Higgs bosons. These two unusual property provided us a way to test NMSSM and distinguish it from MSSM. The main object of this paper is to study the cross section of the e+e− annihilation to produce the Chargino pair associated with the ligth pseudoscalar Higgs radiation (e+e−→χ+χ−A1). From the calculation result, we also con- clude that the cross section of this process is not small in the cases with A1 has a large singlet mixture and χ+χ−A1 has not small coupling. It may be able to detect in the future ILC. We also included the calculation of the proton collider which is for the test at LHC.
Wang, Bo-Ting, and 王柏庭. "Comparison of Two Schemes For Higgs Production Associated with Heavy Quark Pairs using MadGraph." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/54750008927207962091.
Повний текст джерела國立臺灣大學
物理研究所
101
Some Beyond the Standard Model (BSM) Higgs particle may interact strongly with other particles at energy scales presently studied at the LHC, the study of Higgs production associated with heavy quark pairs may help us search for these BSMs. We compare two different schemes, the 4 flavour scheme and the 5 flavour scheme, to describe this process at LO + n jet by merging matrix element and parton shower approach on MadGraph 5 interface to PYTHIA. We show that the 4 flavour scheme may provide better description than the 5 flavour scheme at LO + n jet level.
Sousa, Mário José da Cunha Sargedas de 1984. "Search for the higgs boson at ATLAS/LHC, in associated production with a Z boson." Doctoral thesis, 2017. http://hdl.handle.net/10451/34141.
Повний текст джерелаA mechanism of spontaneous symmetry breaking was used to explain the mass of elementary particles and predicted the existence of the Higgs boson. The Higgs boson was discovered in 2012 by the ATLAS and CMS experiments at the LHC with a mass of about 125 GeV. It now becomes necessary to study this new boson in order to validate the Standard Model of elementary particles. The Standard Model Higgs boson with a mass of 125 GeV decays most of the times to a pair of b-quarks. However, this decay is very difficult to study in a proton-proton collider like the LHC, due to the production of a huge background of b-jets (and also non-b-jets). In the LHC, the only production process with some chance to be used in this study is the associated production with a vector boson, which can decay leptonically allowing the identification of the event. One can use three possibilities: a Z boson decaying to neutrinos (0-lepton channel), a W boson decaying to an electron or muon and a neutrino (1-lepton channel) or a Z boson decaying to a pair of electrons or muons (2-lepton channel). The latter channel is the subject of this thesis. It is an interesting channel because the two charged leptons reduce the multi-jet background more than the other channels and because this channel reconstructs all the particles in the event. The analysis of the 2-lepton channel, known as ZH analysis, considers only events with high quality reconstructed particles. The two charged leptons are required to reconstruct the Z boson and the b-quarks which are reconstructed as jets, are required to be identified as b-jets (b-tagging) for the reconstruction of the Higgs boson. A statistical procedure uses the events selected as input to a likelihood fit to obtain normalisations of the simulated backgrounds from data and simulation comparisons and to extract the signal strength parameter, m, that multiplies the cross section times the branching ratio from the prediction for the Higgs boson from the Standard Model to adjust the ZH signal simulation process to the data. Both muons and electrons, used in the ZH analysis, are much better reconstructed than jets. So, most of the effort in this thesis was dedicated to the improvement of the jet reconstruction, in particular to the energy scale and uncertainty of the jets. I studied two methods to help reduce the systematic uncertainty of the jet energy scale, the leading experimental uncertainty of several physics analysis, with a important contribution to the ZH search, since the Higgs decays to b-quarks that hadronize into jets. First, I created a new trigger with the objective of selecting high-momenta isolated charged hadrons to be used in the determination of the calorimeter response to single hadrons, known as the single hadron response. In addition to extending the momentum range from 10 to 30 GeV, it did so in a high-pileup environment (pileup - number of interactions per proton bunch crossing). This contributed to the validation of the test beam determination of the jet energy scale uncertainty. For jets with pT above 1.8 TeV, for which the current in situ techniques are not able to set the jet energy scale uncertainty, the single hadron response is used to obtain this uncertainty. I have tested a new jet calibration in the ZH analysis: the global sequential calibration (GSC). This method was first developed to reduce the jet energy response dependence on the jet flavour, for gluon and light quark jets. My contribution was the validation and detailed performance studies for b-jets in general, and in particular for b-jets coming from the Higgs boson decay. This new calibration improved the jet energy response by about 2 - 3% and the jet energy resolution by about 20 %. Systematic uncertainties were evaluated for this calibration. I derived specific b-jet systematic uncertainties for this calibration as well as the uncertainties associated to differences between the ATLAS fast and full simulations. The Standard Model Higgs boson decaying in bb⁻ is expected to produce a very small excess of events in the invariant mass distribution of the two b-quarks. We need to have the best possible resolution on this variable and since GSC was found to reduce the b-jet jet energy response resolution, it was applied to the mb¯b distribution. GSC improves the invariant mass resolution up to 18 %. I performed the ZH analysis using a cut-based method and a statistical procedure to obtain the value of the signal strength parameter. A value of µ ⁼ ⁻ 0.69 ≠ 1.29.was obtained. This value is negative, but there is an enormous uncertainty, dominated by the statistical uncertainty, and the result is still compatible with the Standard Model prediction for the Higgs boson.
O mecanismo de quebra espontânea de simetria, que foi utilizado para explicar a massa das partículas elementares do Modelo Padrão, prevê a existência do bosão de Higgs. O bosão de Higgs foi apenas descoberto em 2012 pelas experiências ATLAS e CMS no LHC com uma massa de cerca de 125 GeV. Torna-se agora necessário estudar este novo bosão de modo a validar o Modelo Padrão das partículas elementares. O bosão de Higgs do Modelo Padrão, com uma massa de 125 GeV, vai decair para um par de quarks b na maioria das vezes. No entanto, este decaimento é bastante difícil de estudar num colisionador de protões como o LHC, devido ao enorme fundo de jatos b (e jatos em geral) que são produzidos. No LHC, o único processo de produção com alguma viabilidade para ser usado para estudar este decaimento é a produção associada a um bosão vetorial, que pode decair leptonicamente, proporcionando uma assinatura limpa para identificar o evento. Aqui existem três possibilidades: um bosão Z que decai para neutrinos (canal de 0 leptões), um bosão queWdecai para um eletrão ou um muão carregado e um neutrino (canal de 1 leptão), ou um bosão Z que decai para dois eletrões ou dois muões carregados (canal de 2 leptões). Este último canal foi o escolhido para esta tese. Neste canal a presença de dois leptões carregados reduz o fundo de multi-jatos mais de que nos outros canais e todas as partículas do acontecimento são reconstruidas. A análise do canal de dois leptões, referida como análise ZH, considera apenas acontecimentos com partículas reconstruidas de elevada qualidade. Aos dois leptões é exigido que reconstruam o bosão Z, e os quarks b, que são reconstruidos como jatos, têm de ser identificados como jatos b (b-tagging). Um processo estatístico utiliza os eventos candidatos num ajuste de verosimilhança (likelihood) para obter as normalizações dos fundos simulados e extrair o parâmetro de força do sinal, m, definido como o quociente entre o produto da seção eficaz e a razão de decaimento observados com respeito ao esperado no Modelo Padrão. Tanto os muões como os eletrões, utilizados na análise ZH, são muito melhor reconstruidos do que os jatos. Assim, o maior esforço desta tese concentrou-se para melhorar a reconstrução de jatos, em particular a escala de energia dos jatos e a sua incerteza. Estudei dois métodos que ajudaram a reduzir as incertezas sistemáticas da escala de incerteza dos jatos, que é a maior incerteza sistemática experimental de várias análises de pesquisa, com uma boa contribuição para análise ZH, uma vez que o bosão de Higgs decai para quarks b que hadronizam para jatos. Comecei por criar um novo mecanismo de seleção de acontecimentos (trigger) com o objetivo de escolher hadrões carregados isolados de elevado momento, que seriam utilizados na determinação da resposta em energia do calorímetro a hadrões isolados. Graças a este trigger, passou a ser possível utilizar hadrões isolados produzidos em colisões até um momento de 30 GeV/c, onde este limite era anteriormente de 10 GeV. Com esta amostra de hadrões isolados, pode calibrar-se a resposta do calorímetro em energia, obtendo-se simultaneamente um zona de validação da incerteza determinada para a escala de energia dos jatos hadrónicos a partir de um teste de feixe de partículas com energias bem definidas a partir de 20 GeV. O Trigger mostrou ainda a estabilidade da resposta num ambiente de elevado empilhamento de sinais (pileup - número de interações por colisão de pacotes de protões). Testei uma nova calibração da energia de jatos na análise ZH: a calibração sequencial global (GSC). Este método, foi em primeiro lugar, desenvolvido para reduzir a dependência da resposta em energia dos jatos no sabor dos mesmos (jatos de gluões ou de quarks leves). A minha contribuição foi a validação e o estudo detalhado do desempenho desta calibração para jatos b em geral, e em particular para jatos b provenientes do decaimento do bosão de Higgs. Esta nova calibração melhorou a resposta da energia dos jatos em 2 - 3% e a resolução em energia destes em 20 %. Avaliei os erros sistemáticos, derivei incertezas sistemáticas específicas para jatos b para esta calibração e ainda uma incerteza associada a diferenças entre simulação rápida e completa do detetor ATLAS. Espera-se que o bosão de Higgs do Modelo Padrão a decair em bb⁻ produza um pequeno excesso de eventos na distribuição de massa invariante do par de jatos b. Necessitamos obter a melhor resolução possível nesta variável e, como a calibração GSC mostrou reduzir a resolução em energia dos jatos b, a massa invariante foi também testada com GSC. A utilização desta nova calibração melhorou a resolução em massa até 18 %. Os estudos de validação e desempenho do GSC realizados permitiram a utilização desta calibração na análise do ZH. Desenvolvi uma análise ZH independente utilizando um método de cortes e procedimento estatístico. Obtive para o parâmetro força de sinal o valor µ ⁼ ⁻0.69 ≠ 1.29. Embora negativo, este valor possui uma enorme incerteza, dominada pela incerteza estatística, sendo o resultado ainda compatível com a previsão para o bosão de Higgs feita pelo Modelo Padrão.
Pedro, Rute Costa Batalha 1984. "Search for the higgs boson at ATLAS/LHC in WH associated production and decay to b-quark pairs." Doctoral thesis, 2017. http://hdl.handle.net/10451/34140.
Повний текст джерелаThe Higgs mechanism was incorporated in the Standard Model of elementary particles and interactions in the 1960’s to solve the existent conflict between massive particles and conservation laws of particle physics. A consequence of this mechanism is the prediction of a new fundamental particle, the Higgs boson, observed for the first time in 2012 by the ATLAS and CMS experiments at the Large Hadron Collider. This thesis describes the search for the Higgs decay into a pair of bquarks with the ATLAS experiment, using pp collision events with an 8 TeV center-of-mass energy provided by the LHC in 2012. Although the branching fraction of the H → bb⁻ decay is dominant (BR(H→ bb⁻ ) =57.7% for mH = 125 GeV), this decay mode was not yet observed. The search is particularly challenging given the huge amount of background events containing jets. To reduce this background, the Higgs production associated with aW=Z boson is usually explored, as the leptons resulting from the W=Z decay can effectively trigger the signal. The W associated production with the W boson decaying leptonically is considered. The data analysis searches for events compatible with the W H → lv bb⁻ signal topology: one electron or muon, missing transverse energy associated with the undetected neutrino and two jets resulting from b - quark fragmentation. Events containing jets and charged leptons, as topquark production andW+jets, are the main backgrounds of the analysis. Since their production cross-section is much larger than the signal cross-section, the resulting signal-to-background proportion, (B) S/ √B only 0.3. The analysis comprehends a Multivariate technique, Boosted Decision Tree (BDT), to exploit correlations in the event observables aiming at increasing the sensitivity to the signal. A study that resulted in a 12% gain in the BDT performance was carried on. Samples of signal and background simulated in the same conditions as data are also analysed. Given the small S=pB, it was indispensable to verify that the simulation models correctly the background processes, and to evaluate the systematical uncertainties associated with their prediction. In this context, a study to determine the systematic uncertainties of the single top background modelling was conducted. The ratio between the observed signal event rate and the Standard Model prediction was 1:65⁺0:58 ₋0:56(stat) ⁺0:58 ₋0:48(syst) = 1:65 ⁺0:82₋0:74, and therefore the measurement is compatible with the SM prediction within uncertainties. The signal significance, representing the compatibility between the data observation and the background-only hypothesis, corresponds to the gaussian probability of observing a value larger than 2.02 standard deviations and is not sufficient to state the observation of the W H → lv bb⁻ process.
O mecanismo de Higgs foi introduzido no Modelo Padrão das partículas elementares e suas interacção¸ na década de 1960, para resolver o conflito existente entre partículas massivas e leis de conservação da física de partículas. Uma das consequências deste mecanismo ´e a previsão de uma nova partícula fundamental, o bosão de Higgs, observado pela primeira vez em 2012 pelas experiencias ATLAS e CMS do LHC/CERN. Esta tese descreve a pesquisa pelo bosão de Higgs através do seu decaimento em pares de quarks b com o detector ATLAS, usando acontecimentos de colisões pp com uma energia de centro-de-massa de 8 TeV. Este modo de decaimento ainda não foi observado, embora a razão de bifurcação (BR) seja dominante relativamente aos processos alternativos: para um Higgs de massa mH = 125 GeV, BR(H → lv bb⁻) =57.7%. A sua procura ´e desafiante e difícil devido à quantidade de acontecimentos de fundo com jactos de partículas. Para reduzir esse fundo, escolhe-se a produção do bosão de Higgs associada a um bosão W=Z, uma vez que os leptões resultantes do decaimento do W=Z constituem uma forma efectiva de identificar o sinal. Considera-se a produção associada a umW e seleccionam-se os acontecimentos de acordo com a topologia do sinal W H → lv bb⁻ : um electrão ou um muão, energia em falta associada ao neutrino e dois jactos resultantes da fragmentação dos quarks b. Acontecimentos que resultam em jactos e leptões carregados, como a produção¸ de quarks top e de W+jactos, constituem os fundos principais da análise. Como a seccão eficaz de produção¸ ˜ao destes processos ´e muito superior à do sinal, a proporção de acontecimentos de sinal (S) e fundo (B) S/ √B e de apenas 0.3. A análise usa uma t´técnica Multivariacional, que explora correlações entre diferentes observáveis através do método Boosted Decision Tree (BDT), para aumentar a sensibilidade aos acontecimentos de sinal. Realizou-se um estudo que permitiu melhorar o desempenho da BDT até 12%. São também analisadas amostras de simulação de sinal e fundos nas mesmas condicões. Dada a pequena significância do sinal relativamente ao fundo, foi indispensável verificar que a simulação modela correctamente os fundos e avaliar as incertezas sistemáticas na sua previsão. Neste contexto, foi efectuado um estudo que levou `a determinação das incertezas sistemáticas associadas `a modelação da produção¸ do quark top. A razão entre a taxa de acontecimentos de sinal observada e a prevista pelo Modelo Padrão foi 1:65⁺0:58 ₋0:56(stat) ⁺0:58 ₋0:48(syst) = 1:65 ⁺0:82, medida compatível com a previsão tendo em conta as incertezas obtidas. A significância do sinal medido, que representa a probabilidade dos dados observados serem compatíveis com a hipótese de ausência de sinal, corresponde `a probabilidade gaussiana de observar um valor superior a 2.02 desvios padrão e ´e insuficiente para se declarar a observação do processo W H → lv bb⁻.
Brelier, Bertrand. "Étude de la production associée ZH/WH, H - ±gamma gamma» avec le détecteur ATLAS." Thèse, 2008. http://hdl.handle.net/1866/6407.
Повний текст джерелаCoelho, Luis Felipe Falda de Ulhoa. "Study of the CP nature of the top-Higgs coupling in ttH production at the LHC." Master's thesis, 2020. http://hdl.handle.net/10316/92144.
Повний текст джерелаNo Modelo Padrão (SM), é previsto que o bosão de Higgs seja uma partícula escalar e que suas interações não violem a simetria CP. Após a observação da produção do bosão de Higgs em associação com um par de quarks top (ttH) pelas experiências ATLAS e CMS em 2018, a observação de uma componente ímpar à transformações de carga-paridade (CP) em um dos acoplamentos do bosão de Higgs constituiria uma importante descoberta de física além do SM (BSM). Recentemente, ATLAS e CMS procuraram essa componente em eventos ttH com o Higgs decaindo em dois fotões. No entanto, o acoplamento entre o Higgs e os fotões é induzido por loops e pode ser afetado por efeitos da nova física. Esta tese descreve o estudo da natureza CP do acoplamento de Yukawa do Higgs aos quarks top por meio da análise de eventos ttH no canal de decaimento H→bb, e fornece projeções deste estudo do Run 2 do Large Hadron Collider (LHC) ao LHC de alta luminosidade (HL-LHC). A análise usa dados de colisão protão-protão coletados com o detector ATLAS durante o período do Run 2 do Grande Colisor de Hadrões (LHC) com uma energia de centro de massa de √s=13 TeV e luminosidade integrada total de 139 fb-1. São usados apenas eventos contendo um ou dois leptões no estado final do decaimento do par de quarks top. Em seguida, os eventos são classificados em regiões de acordo com o número de jatos e o número de b-jatos marcados usando ponto de operação (WPs) de 60% and 70%. Várias técnicas multivariadas foram usadas para melhorar a sensibilidade da análise, uma árvore da decisão reforçada (BDT) foi treinada para separar o sinal do fundo e outra para distinguir entre diferentes cenários de CP. Variáveis sensíveis ao CP, incluindo observáveis calculadas no referencial de laboratório e variáveis angulares calculadas em referenciais específicos, foram usadas no ajuste e no treinamento das BDTs.Um ajuste de verossimilhança é executado em todas as regiões de análise para restringir as previsões de fundo e reduzir as incertezas sistemáticas. O valor esperado para o ângulo de mistura CP é obtido desse ajuste. Além disso, uma extrapolação da análise foi realizada nesta tese, a fim de fornecer projeções sobre a medição do ângulo de mistura de CP para o LHC de alta luminosidade (HL-LHC). Foram considerados diferentes cenários para a evolução das incertezas sistemáticas com o aumento esperado da luminosidade. O valor esperado para o ângulo de mistura de CP foi obtido para vários valores diferentes de luminosidade até 3000 fb-1. Com as atuais incertezas sistemáticas, espera-se que a produção de ttH pura CP-ímpar seja excluída com 99.73\% de nível de confiança (CL) apenas no final do projeto HL-LHC. A significância de exclusão CP-ímpar é representada em função da luminosidade para cada um dos cenários considerados, e os efeitos dos vários tipos de incertezas são avaliados.
In the Standard Model (SM), the Higgs boson is predicted to be a scalar particle with no CP-violating interactions. After the observation of the Higgs boson production in association with a top quark pair (ttH) by ATLAS and CMS in 2018, the measurement of an odd charge-parity (CP) component in one of the Higgs boson couplings would constitute an important discovery of physics beyond the SM (BSM). Recently, ATLAS and CMS searched for such a component in ttH events with the Higgs decaying into two photons. However, the coupling between the Higgs and the photons is loop-induced and could be modified by effects of new physics. This thesis describes the study of the CP nature of the Higgs Yukawa coupling to the top quarks by analyzing ttH events in the H→bb decay channel, and provides projections of this search from the Large Hadron Collider (LHC) Run 2 to the High-Luminosity LHC (HL-LHC). The analysis uses the full Run 2 dataset of proton-proton collision collected with the ATLAS detector at a center-of-mass energy of √s=13 TeV and total integrated luminosity of 139 fb-1. Only events containing either one or two leptons in the final state from the decay of the top quark pair are used in the analysis. Then, the events are classified into regions according to the number of jets and the number of b-tagged jets using the 60% and 70% working points (WPs). Two sets of multivariate classifiers are utilized to improve the analysis sensitivity. One classifier targets the classification of signal against backgrounds and the other targets the separation between different CP scenarios. Several CP sensitive variables, including lab-frame observables and angular variables calculated in specific frames, were used in the training of the BDTs. A profile likelihood fit is performed over all analysis regions to constrain the background predictions and reduce the systematic uncertainties. The expected value for the CP-mixing angle is presented. An extrapolation of the analysis is performed in order to provide projections on the measurement of the CP-mixing angle for the HL-LHC. Different scenarios for the evolution of the systematic uncertainties with the expected increase in the luminosity were considered. The expected value for the CP-mixing angle was obtained for several different values of luminosity up to 3000 fb-1. With the current systematic uncertainties, the pure CP-odd ttH production is expected to be excluded with 99.73% confidence level (CL) only at the end of the HL-LHC project. The CP-odd exclusion significance is represented as a function of the luminosity for each of the scenarios considered, and the effects of the various types of uncertainties are evaluated.
Outro - FCT CERN/FIS-PAR/0002/2019
Fugel, Frank [Verfasser]. "Associated production of higgs bosons and heavy quarks in two photon collisions at next-to-leading order / vorgelegt von Frank Fugel." 2007. http://d-nb.info/986396370/34.
Повний текст джерелаWarsinsky, Markus [Verfasser]. "Studies of b-associated production and muonic decays of neutral Higgs bosons at the ATLAS experiment within the minimal supersymmetric standard model / von Markus Warsinsky." 2008. http://d-nb.info/990711161/34.
Повний текст джерела