Дисертації з теми "Flavour changing"
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Smith, Daniel. "Study of the flavour changing neutral current β-s#gamma# at BaBar." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272066.
Повний текст джерелаLin, Chi-Jen David. "Flavour changing neutral current processes of B and K mesons from lattice QCD." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/12420.
Повний текст джерелаCotellucci, Alessandro. "Flavour constraints on sequestered supersymmetry breaking in string models." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21709/.
Повний текст джерелаKachanovich, Aliaksei [Verfasser], and U. [Akademischer Betreuer] Nierste. "Flavour-changing neutral current processes beyond the Standard Model / Aliaksei Kachanovich ; Betreuer: U. Nierste." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/123047577X/34.
Повний текст джерелаKennedy, John James. "A search for single top-quark production and flavour-changing neutral-current interactions at H1." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269575.
Повний текст джерелаWolff, Robert. "Searches for ttH and flavour-changing t –> Hq productions in multileptonic final states with the ATLAS detector." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0304/document.
Повний текст джерелаThis doctoral thesis describes the search for the associated Higgs boson production with a pair of top quarks (tt̅H) in a dataset of proton-proton collisions at a center-of-mass energy of √s = 13 TeV and with an integrated luminosity of 36.1 fb⁻¹, recorded by the ATLAS detector in 2015 and 2016. Seven final states, associated to different Higgs boson decay, are optimised to get the best signal to background separation. An excess of events over the SM background is observed with a significance of 4.1 standard deviations, while 2.8 are expected. In combination with search results obtained for other Higgs boson decay channels, the tt̅H production has been discovered with the ATLAS detector using up to 79.8 fb⁻¹ of collision data at √s = 7, 8 and 13 TeV.Flavour-changing neutral currents in top quark decays into a Higgs boson and a light up-type quark (t → Hq) are strongly suppressed in the SM. New physics models can predict a t → Hc decay branching ratio of 0.15%. The search for these decays in final states with two or three leptons observes no signal. An upper limit on the t → Hc (t → Hu) decay branching ratio at a 95% confidence level is set at 0.16% (0.19%) with an expected limit of 0.15% (0.15%).To bypass the limitation of an insufficient amount of collision data, the LHC and its experiments foresee an ambitious upgrade plan. The current ATLAS Liquid Argon Calorimeter readout will be replaced to get an increased granularity to improve the trigger selectivity and avoid bandwidth saturation at high luminosity. A demonstrator system has been operated since 2015 and its performance studied with calibration and collision data
Friedrich, Conrad. "Search for single top-quark production via flavour-changing neutral currents in strong interactions using s = 8 TeV ATLAS data." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2015. http://dx.doi.org/10.18452/17348.
Повний текст джерелаThis thesis presents results of a search for single top-quark production via flavour-changing neutral currents (FCNCs) in strong interactions using data recorded with the ATLAS experiment at the Large Hadron Collider in 2012. A dataset from proton-proton collisions at a centre-of-mass energy of 8TeV and corresponding to an integrated luminosity of 14.1 fb−1 is used. It is searched for FCNC events in which a light quark (u or c) interacts with a gluon to produce a single top quark, either with or without the associated production of another light quark or gluon. Candidate events of leptonically decaying top-quarks are selected by requiring a single electron or muon, a substantial amount of missing transverse energy, and exactly one or two jets of which exactly one has to fulfil a b-tagging criterion. Multivariate techniques are employed in order to distinguish between signal- and background-like events by making use of artificial neural networks that combine multiple kinematic variables into a single classifier output. A Bayesian statistical analysis is performed on the classifier outputs in order to quantify potential signs of FCNC single top-quark production. No excess in signal events is observed and the results are in agreement with the theory predictions. Consequently a new upper limit is set on the FCNC single top-quark production cross-section multiplied by the t->Wb branching fraction. Using theory calculations within a model-independent effective theory framework, this limit is converted into upper limits on the coupling constants of the FCNC interactions as well as into respective upper limits on the branching fractions.
Alhroob, Muhammad [Verfasser]. "Search for Flavour Changing Neutral Currents in Single Top-Quark Production at √s = 7 TeV with the ATLAS Detector / Muhammad Alhroob." Bonn : Universitäts- und Landesbibliothek Bonn, 2013. http://d-nb.info/1044869984/34.
Повний текст джерелаArslan, Ozan [Verfasser]. "Search for Flavour Changing Neutral Currents through Single Top-Quark Production at radix 8 TeV with the ATLAS Detector / Ozan Arslan." Bonn : Universitäts- und Landesbibliothek Bonn, 2017. http://d-nb.info/114974491X/34.
Повний текст джерелаAlpigiani, Cristiano. "Search for rare B decays into two muons with the ATLAS detector." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8922.
Повний текст джерелаMollet, Simon. "Exploration of 6-dimensional models with non trivial topology and their predictions for fermions masses and mixings, neutrino physics, flavour changing interactions and CP violation." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/230863.
Повний текст джерелаDoctorat en Sciences
info:eu-repo/semantics/nonPublished
Friedrich, Conrad [Verfasser], Ulrich [Akademischer Betreuer] Husemann, Heiko [Akademischer Betreuer] Lacker, and Arno [Akademischer Betreuer] Straessner. "Search for single top-quark production via flavour-changing neutral currents in strong interactions using s = 8 TeV ATLAS data / Conrad Friedrich. Gutachter: Ulrich Husemann ; Heiko Lacker ; Arno Straessner." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2015. http://d-nb.info/1078666466/34.
Повний текст джерелаBorsato, Martino. "Study of the BO to Kstar0 electron positron decay with the LHCb detector and development of a novel concept of PID detector : the Focusing DIRC." Sorbonne Paris Cité, 2015. https://theses.hal.science/tel-01456521.
Повний текст джерелаFlavour-changing neutral current processes of the type b --+ sy are forbidden at the tree level in the Standard Model (SM) and occur at leading order through radiative loop diagrams. Therefore, they are sensitive to new physics (NP), which may contrebute either at the tree or loop level. Furthermore, the chirality of the weak interaction in the SM implies that the photon emitted has left-handed polarisation. However, a whole class of NP theories do not share this SM feature and may manifest unambiguously as a right-handed contribution to the polarisation. This thesis presents the first study of the b-* sy photon polarisation through an angular analysis of the B0-*K* 0 e+e- channel. Even though BO-*K* 0 e+e- is not a radiative b s transition, the contribution from a virtual photon coupling to the lepton pair dominates in the low-q2 region. Furthermore, the channel with electrons rather than muons allows to better isolate the virtual photon contribution at the low end of the q 2 spectrum. The integrated luminosity of 3 fb-1 collected by LHCb during LHC Run 1 allowed for the first time to select a sample of B0-›K* 0 e+e- events large enough to measure the transverse asymmetries AT(2)=-0. 23±0. 23±0. 05 and ATIm=0. 14±0. 22±0. 05 in the low q2 region between 0. 002 GeV2/c4 and 1 GeV2/c4. These measurements are found to be consistent with SM predictions and provide new constraints on right handed contributions to the photon polarisation at the same level of precision as the ones from measurements involving radiative decays. Flavour physics experiments require advanced detectors dedicated to the identification of the different flavours of charged hadrons. Most of them are based on the detection of the Cherenkov light emitted by these particles as they traverse a dielectric medium. This thesis presents also the R&D activity on a new detector concept based on the BABAR DIRC, the FDIRC. Its design is intended to operate the detector in an environment with background two orders of magnitude larger than BABAR thanks to a faster and smaller imaging camera made of radiation-hard fused silica. The first full-scale prototype of the FDIRC was tested at the SLAC Cosmic Ray Telescope and demonstrated the feasibility of the detector concept
Geßner, Gregor [Verfasser], Kevin [Akademischer Betreuer] Kröninger, and Wolfgang [Gutachter] Wagner. "Search for flavour-changing neutral currents in processes with a single top quark in association with a photon using a deep neural network at the ATLAS experiment at √s = 13TeV / Gregor Geßner ; Gutachter: Wolfgang Wagner ; Betreuer: Kevin Kröninger." Dortmund : Universitätsbibliothek Dortmund, 2019. http://d-nb.info/1203373015/34.
Повний текст джерелаQuintana, Boris. "Search for radiative B decays to orbitally excited mesons at LHCb." Thesis, Université Clermont Auvergne (2017-2020), 2019. http://www.theses.fr/2019CLFAC060.
Повний текст джерелаThis document presents studies of radiative decays of B0 and Bs mesons to orbitally excited states, produced in proton collisions at the Large Hadron Collider (LHC) of CERN (European Council for Nuclear Research). It takes place in the context of the search for new physics processes beyond the standard model of particle physics. The work is based on the data collected at the LHCb experiment during the Run 1(2011-2012) and the Run 2 (2015-2018) of the LHC, which corresponds to an integrated luminosity of about 8.7 fb−1. First, an optimised selection of the final states comprising of two charged tracks and a high energy photon is put in place, regrouping a large samples of B hadron radiative decays. Then, a mass model is fit to the data distribution, allowing to statistically subtract the background contributions in the data set.A first amplitude analysis is then developed to study the hadronic structure in the Bs → K+K−γ decay mode. Resulting from this analysis is the first observation of the Bs → f2j (1525)γ mode together with a relative branching ratio measurement:B(Bs → f2j γ) = (24.1 ± 0.9 (stat) +1.6 (syst) ± 0.6 (br)) × 10−2B(Bs → φγ) −0.8It is the second radiative decay mode observed for the Bs meson. A similar analysis is performed on the B0 → K±π∓γ mode, allowing a preliminary measurement of the relative branching ratio of B0 → K2∗(1430)γ:(B0 K∗0(1430)γ)B(B0 → K∗0(892)γ) = (36.4 ± 0.4 (stat) ± 1.3(BR))%However, a detailed systematics study is needed to assess its competitivity with previous measurements of this decay mode. Making use of a similar selection strategy, a preliminary study of B K0hhγ modes is also set up during the thesis to estimate the available statistics for these modes at LHCb, which are particularly interesting to measure the photon polarisation in the b sγ transition. This work will be the starting point of an analysis comprising the future data that will be collected during the Run 3 of the LHC
Walston, Sean Eric. "Heavy flavor decays of the Z⁰ and a search for flavor changing neutral currents /." wwwlib.umi.com/cr/uoregon/fullcit?p3136452 view abstract or download file of text, 2004.
Знайти повний текст джерелаTypescript. Includes vita and abstract. Includes bibliographical references (leaves 254-261). Also available for download via the World Wide Web; free to University of Oregon users.
Jäger, Sebastian. "Supersymmetric SO(10) unification and flavor changing weak decays." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969864647.
Повний текст джерелаWitchey, Nicholas James. "Search for flavor changing neutral current decays of charm mesons /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487935125882463.
Повний текст джерелаPoschenrieder, Anton. "The Littlest Higgs and its phenomenological implications for flavor changing neutral currents and lepton flavor violating processes." kostenfrei, 2007. http://mediatum2.ub.tum.de/doc/626143/626143.pdf.
Повний текст джерелаAmanik, Philip. "Effects of non-standard neutrino flavor changing interactions in core collapse supernovae." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3216385.
Повний текст джерелаTitle from first page of PDF file (viewed September 5, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 87-89).
Kochebina, Olga. "Study of Rare Charm Decays with the LHCb Detector at CERN." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112208/document.
Повний текст джерелаRare charm decays proceed mostly through the c -> u Flavor Changing Neutral Current (FCNC), which is possible only at loop level in the Standard Model (SM). In charmed decays, FCNCs are subject to a very efficient GIM suppression, leading to very rare processes. Consequently, rare charm decays are good tools to probe to New Physics (NP) beyond the SM. NP particles could become detectable by causing observables such as branching ratios and CP or angular asymmetries to deviate from the SM predictions. The main subject of this thesis is the measurement of the branching ratio of the D0 -> K-π+ ρ/ω (->µ+µ-) mode. It will be precious in the future, in particular as a normalization mode in the study of all: D0 -> h-h’+ µ+µ- decays D0 -> K-π+µ+µ-, D0 -> π+π-µ+µ-, D0 -> K+K-µ+µ- and D0 -> K+π-µ+µ-. Using 2/fb of 2012 LHCb data we find: B(D0 -> K-π+ ρ/ω (->µ+µ-)) = (4.37± 0.12(stat.) ±0.53(syst.)) ×10^-6. This is the first measurement of this mode. We also determined sensitivities to total and partial branching fractions and asymmetries in D0 -> h-h’+ µ+µ- decays with future LHCb datasets. In addition, the systematic uncertainties affecting the searches for the 3-body decays, D+(s) -> π+µ+µ- and D+(s) -> π-µ+µ+, carried out by LHCb based on the data collected in 2011 (1/fb). Finally, the results of the tests of front-end electronic board for the Upgrade of LHCb are presented
Turan, Ismail. "Flavor Changing Neutral Current Processes In The Framework Of The Two Higgs Doublet Model." Phd thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/717843/index.pdf.
Повний текст джерелаShinohara, Satoshi. "Study of the KL→π⁰ννDecay at the J-PARC KOTO Experiment". Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/265175.
Повний текст джерелаBéjar, Latonda Santiago. "Flavor changing neutral decay effects in models with two Higgs boson doublets: Applications to LHC Physics." Doctoral thesis, Universitat Autònoma de Barcelona, 2006. http://hdl.handle.net/10803/3375.
Повний текст джерелаNicol, Michelle. "Analysis of the rare decay B->K*ee at LHCb." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112354/document.
Повний текст джерелаThe high bb cross section produced by the LHC offers an excellent opportunity for thestudy of flavour changing neutral current B decays, where the effects of new physics can be probed. This thesis presents an analysis of the rare decay B->K*ee which can be used to measure the polarisation of the photon in the b -> s transition. When the dilepton mass is low, the ee pair comes predominantly from a virtual photon, and the polarisation can be accessed via an angular analysis. It is predicted to be predominantly left handed in the Standard Model, and therefore an enhanced right handed amplitude would be a sign of new physics. A first step is to measure the branching fraction in the dilepton mass range, 30 MeV to 1 GeV. This decay has not yet been observed in this region, due to its small branching ratio. The analysis involves electrons with low transverse momentum, and is thus experimentally complex in the hadronic environment at the LHC. The branching ratio is measured relative to that of B->J/Psi(ee)K*, which eliminates both certain experimental effects, and the need to determine absolute effciencies. The result is obtained with an integrated luminosity of 1 fb-1 of pp collisions, collected by LHCb during 2011 and is found to be:B(B->K*ee)30-1000MeV = (3:19+0:75-0:68(stat) +/- 0:21(syst) =/-0.15(PDG) x10-7 when using the PDG value for the B->J/Psi(ee)K* branching ratio. The last part of the thesis presents Monte Carlo studies, showing that with the inclusion of the 2012 data sample, the expected sensitivity on the fraction of right handed polarisation is approximately 0.1, which is comparable with the world average obtained with different methods
Sumensari, Olcyr. "Search of new physics through flavor physics observables." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS315/document.
Повний текст джерелаIndirect searches of physics beyond the Standard Model through flavor physics processes at low energies are complementary to the ongoing efforts at the LHC to observe the New Physic phenomena directly. In this thesis we discuss several scenarios of physics beyond the Standard Model by (a) reusing the effective field theory approach and (b) by considering explicit extensions of the Standard Model, namely the two-Higgs doublet models and the scenarios involving the low energy scalar leptoquark states. Particular emphasis is devoted to the issue of the lepton flavor universality violation in the exclusive decays based on b → sℓℓ and b → cτν, and to the possibility of searching for signs of lepton flavor violation through similar decay modes. A proposal for testing the presence of the light CP-odd Higgs through quarkonia decays is also made
Eygi, Zeynep Deniz. "The Standard Model Analyasis Of The Cp Violation In The Inclusive Semileptonic B-meson Decays." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12604712/index.pdf.
Повний текст джерелаviolating asymmetry and CP &ndash
violating asymmetry in the forward-backward asymmetry in these processes are examined.The dependencies of these physical parameters on the Standard Model parametres are analyzed by paying a special attention to the long distance effects. Although the branching ratios predicted for the inclusive semileptonic B- meson decays are relatively small because of CKM suppression , it has been found that there is a significant ACP and ACP(AFB) for these processes.
Acar, Hilal. "The Inclusive Semileptonic Decays Of The B-meson In A Cp Softly Broken Two Higgs Doublet Model." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604766/index.pdf.
Повний текст джерелаX_dell ell decays are examined in the context of a CP softly broken two Higgs doublet model. The differential branching ratio, forward-backward asymmetry, CP-violating asymmetry, CP-violating asymmetry in the forward-backward asymmetry and polarization asymmetries of the final lepton in this decay are studied. The dependencies of these physical parameters on the model parameters are analyzed by paying a special attention to the effects of neutral Higgs boson (NHB) exchanges and possible CP violating effects. It has been found that NHB effects are quite significant for the tau mode and the above-mentioned observables seems to be promising as a testing ground for new physics beyond the SM, especially for the existence of the CP-violating phase in the theory.
Yilmaz, Umit Oktay. "The Polarization Properties Of The Final State Particles In The Rare Radiative B-meson Decay." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606100/index.pdf.
Повний текст джерела#8594
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l+l- decay by using the most general model independent form of the effective Hamiltonian is presented. The total and the differential branching ratios for these decays, when photon is in the positive and negative helicity states, are studied. The sensitivity of "
photon polarization asymmetry"
and the longitudinal, transverse and normal polarization asymmetries of final state leptons, as well as lepton-antilepton combined asymmetries in Bs &
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l+l- decay to the new Wilson coefficients are also investigated. It is shown that all these physical observables are very sensitive to the existence of new physics beyond SM and their experimental measurements can give valuable information about it.
Brost, Elizabeth. "Search for the Flavor-Changing Neutral Current in Top Pair Events in sqrt(s) = 8 TeV Proton-Proton Collisions at the Large Hadron Collider Using the ATLAS Detector." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20406.
Повний текст джерелаTsiskaridze, Shota. "Search for avor-changing neutral current top quark decays t—›Hq, with H—›bb, in pp collisions at √s = 8 TeV with the ATLAS detector." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/387229.
Повний текст джерелаIn this dissertation a search for avour-changing neutral currents in the decay of a top quark to an up-type quark (q = u; c) and the Standard Model Higgs boson, where the Higgs boson decays to bb, is presented. The analysis searches for top quark pair events in which one top quark decays to Wb, with the W boson decaying leptonically, and the other top quark decays to Hq. The search is based on pp collisions at √s = 8 TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and uses an integrated luminosity of 20.3 fb-1. Data are analyzed in the lepton+jets final state, characterized by an isolated electron or muon with moderately high transverse momentum and at least four jets. The search exploits the high multiplicity of b jets characteristic of signal events, and employs a likelihood discriminant that uses the kinematic differences between the signal and the background, which is dominated by tt—›WbWb decays. No significant excess of events above the background expectation is found. The observed (expected) upper limits on the t—›Hc and t—›Hu branching ratios are 0.56% (0.42%) and 0.61% (0.64%) respectively, at the 95% confidence level. The combination of this search with other ATLAS searches in the H—› and H—›WW*,tt decay modes significantly improves the sensitivity yielding observed (expected) upper limits on the t—›Hc and t—›Hu branching ratios of 0.46% (0.25%) and 0.45% (0.29%) respectively, at the 95% confidence level. The corresponding combined ob- served (expected) upper limits on the | tcH| and | tuH| couplings are 0.13 (0.10) and 0.13 (0.10) respectively. These are the most restrictive direct bounds to date on tqH interactions measured so far.
Davidkov, Momchil [Verfasser]. "Supersymmetric flavour changing neutral currents beyond minimal flavour violation / von Momchil Davidkov." 2010. http://d-nb.info/1008485683/34.
Повний текст джерелаWon, Miguel Daiyen Carvalho. "Flavour-Changing-Neutral-Currents in Top Quark Physics." Doctoral thesis, 2014. http://hdl.handle.net/10316/24325.
Повний текст джерелаThis work presents a study on top quark avour-changing-neutralcurrents (FCNC) interaction. These interactions are characterised by a vertex with a top quark and a light u or c quark, together with one of the neutral gauge bosons: gluon, photon and Z boson. They are highly suppressed in the Standard Model (SM), and are therefore a good place to search for physics beyond the SM. We start by presenting a theoretical introduction divided in three chapters. The rst one is dedicated to the subject of collider physics, where the main aspects related to the physics and mathematical background of collider experiments are discussed. A brief account of the SM is then given followed by a more detailed chapter where the subject of E ective Theories and its use in FCNC top quark physics is described. In the following chapters we rst present a study where improvement of FCNC top quark interaction limits were tested in an electronpositron collider. A post LHC scenario where no FCNC physics is found was assumed. In the next chapter we present a study on the well-known asymmetry measured in top quark pair production at the Tevatron, and its deviation in respect to the SM prediction. The study addresses the problem using a set of six dimension e ective operators in order to reproduce this asymmetry. In the following chapter a new Monte Carlo event generator, MEtop, is presented. It is a generator conceived primarily for FCNC direct top events with LO and NLO precision, but it also generates FCNC single top @ LO. The generator allows the user to generate events from three di erent sets of e ective operators. Finally, experimental simulations were performed in order to study the performance of MEtop in FCNC top quark search @ LHC.
FCT - SFRH/BD/45041/2008
Guedes, Júnior Renato Batista 1968. "Flavour changing at colliders in the effective theory approach." Doctoral thesis, 2008. http://hdl.handle.net/10451/1565.
Повний текст джерелаPeixoto, Ana Paula Pereira. "Search for tZ production via Flavour Changing Neutral Currents with the ATLAS experiment at the LHC." Master's thesis, 2016. http://hdl.handle.net/1822/56022.
Повний текст джерелаThe subject of the present dissertation is the search for tZ event production by Flavour Changing Neutral Currents (FCNC) through the analysis of data collected by the ATLAS detector of the Large Hadron Collider located in CERN. The FCNC processes are very rare in the Standard Model of Particle Physics since they are not allowed at tree-level and extremely suppressed at loop-level. However, this processes have a higher probability to occur in several models beyond the Standard Model. In this thesis, a search for the production of a top quark and a boson Z via FCNC in a trileptonic topology is discussed. The final state of the tZ production consists in a pair of leptons with opposite sign and same flavour having a mass compatible with the decay of a Z boson, a charged lepton and a neutral lepton classified as coming from the decay of a top quark and finally a jet coming from a bottom quark (b-tagged jet). The analyzed data coming from proton-proton collisions at the centre-of-mass energy of √s = 13 TeV was collected in the data-taking period between July and November of 2015 corresponding to an integrated luminosity of 3.21 fb−1. A complementary study of possible discriminant variables is presented. Through this study, expected upper limits at 95% confidence level on the cross-section of tZ production via FCNC were obtained. An interpretation of these limits in terms of branching ratios for t → qZ and the tZq coupling is also presented.
A presente dissertação tem como objectivo a pesquisa da produção de eventos tZ através de processos de mudança de sabor por correntes neutras recorrendo a uma análise de dados colectados pelo detector ATLAS do Large Hadron Collider localizado no CERN. Os processos de mudança de sabor por correntes neutras são muito raros no Modelo Padrão da Física de Partículas, sendo ausentes a tree-level e extremamente suprimidos a loop-level. No entanto, estes processos têm uma maior probabilidade de ocorrer em vários modelos para além do Modelo Padrão. Neste trabalho é estudada a produção de um quark top e de um bosão Z através de processos de mudança de sabor por correntes neutras numa topologia trileptónica. O estado final desta pesquisa consiste num par de leptões de carga oposta e sabor idêntico com uma massa compatível com o decaimento de um bosão Z, um leptão carregado em conjunto com um leptão neutro provenientes do decaimento de um quark top e finalmente um jacto proveniente de um quark bottom (b-tagged jet). Os dados analisados, relativos a colisões protão-protão a uma energia de centro de massa de √s = 13 TeV, foram obtidos no período de Julho a Novembro de 2015 correspondendo a uma luminosidade integrada de 3.21 fb−1. Um estudo complementar de possíveis variáveis discriminantes é apresentado. Através deste estudo, são obtidos limites superiores esperados com um nível de confiança de 95% na secção eficaz de produção deste processo. Estes limites são interpretados em termos do acoplamento tZq e da fracção de decaimento t → qZ.
Laboratório de Instrumentação e Física Experimental de Partículas, FCT/MEC (Fundação Ciência e Tecnologia /Ministério da Educação e da Ciência), FEDER (Fundo Europeu de Desenvolvimento Regional) for funding my activities this past year, as established by the partnership PT2020 partnership with COMPETE2020 (Autoridade de Gestão do Programa Operacional Competitividade e Internacionalização), by providing me with a research scholarship (Reference LIP/BI-26/2015).
Weiler, Andreas [Verfasser]. "Minimal flavour violation in the quark and lepton sector and the impact of extra dimensions on flavour changing neutral currents and electroweak symmetry breaking / vorgelegt von Andreas Weiler." 2007. http://d-nb.info/988098083/34.
Повний текст джерелаVeloso, Filipe Manuel Almeida. "Study of ATLAS sensitivity to FCNC top quark decays." Doctoral thesis, 2008. http://hdl.handle.net/10316/7517.
Повний текст джерелаJäger, Sebastian [Verfasser]. "Supersymmetric SO(10) unification and flavor changing weak decays / Sebastian Jäger." 2003. http://d-nb.info/969864647/34.
Повний текст джерелаPoschenrieder, Anton [Verfasser]. "The littlest Higgs and its phenomenological implications for flavor changing neutral currents and lepton flavor violating processes / Anton Poschenrieder." 2007. http://d-nb.info/988908255/34.
Повний текст джерелаLee, Yun-Han, and 李昀翰. "Search for top decays through flavor changing neutral current process, t→Z+q, in pp collisions at √s=8 TeV." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/79701030770203938456.
Повний текст джерела國立臺灣大學
物理研究所
101
In the standard model, cross-generation interactions mediated by Z bosons, known as the flavor-changing neutral current (FCNC), are highly suppressed. For top quark FCNC decay, the cross-section is far below the experimental limit. However, other models predict much higher cross-sections, and some of them are even within reach. Therefore, using the data sample corresponding to an integrated luminosity of 19.5 fb^−1 proton-proton collisions at a center-of-mass energy 8TeV , collected with the CMS detector at the LHC, we performed the search with the decay chain t¯t to Wb+Zq, where W decays to a charged lepton and a neutrino and Z decays to two charged leptons. The data-driven analysis using b-tagging method is performed with the estimated background being 3.08±0.85±0.76, which is consistent with the estimation of Monte-Carlo method. One event is observed in the data which is consistent with the expected background, and the upper limit of the branching fraction for t to Z+q is calculated as 0.06% at the 95% confidence level.