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Study of Z + b-jets production at LHC energies using CMS detector

The most successful theory in particle physics is the Standard Model (SM), which describes the fundamental particles and their interactions. The majority of SM predictions have been tested successfully with excellent precision. Despite its achievements, SM fails to resolve many key problems such as...

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Autor principal: Meena, Meena
Lenguaje:eng
Publicado: 2023
Materias:
Acceso en línea:http://cds.cern.ch/record/2866200
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author Meena, Meena
author_facet Meena, Meena
author_sort Meena, Meena
collection CERN
description The most successful theory in particle physics is the Standard Model (SM), which describes the fundamental particles and their interactions. The majority of SM predictions have been tested successfully with excellent precision. Despite its achievements, SM fails to resolve many key problems such as the inclusion of gravity, absence of dark matter, and unification of the gauge couplings at high energies, etc. Many scenarios beyond Standard Model (BSM) have been proposed to explain some of these aspects. To test the predictions of the SM and BSM scenarios several experiments have been designed and built. Among them, the Large Hadron Collider at the European Council for Nuclear Research is the largest and most powerful particle accelerator ever built. The proton beams are made to collide at four different locations along the LHC ring. At these positions, four giant detectors are placed to record every possible outcome of the collision. The Compact Muon Solenoid (CMS) is one of its general purpose detectors designed for SM measurements and BSM searches due to its high precision detection of particles from collision events. This thesis is based on two aspects: hardware work and physics analysis. This present work includes the assembly and testing of the Gas Electron Multiplier based GE1/1 subdetectors, which are used for the upgrade of the first endcap muon station of the CMS detector during the Long Shutdown2 period (December 2018–April 2022). The GE1/1 subdetectors have added redundancy to the muon subsystem of the CMS detector in the forward regions (higher η) and improved the triggering and muon tracks reconstruction capabilities. The GE1/1 chambers have an excellent detection efficiency of more than 97% with time and position resolution of 10 ns and 260 μm to 340 μm, respectively. The CMS GE1/1 upgrade project required the fabrication and testing of 144 GE1/1 chambers. India contributed to the CMS GE1/1 upgrade project, which included the assembly and testing of the GE1/1 chambers, which was carried out at Panjab University, Chandigarh, in collaboration with Delhi University, Delhi, and Bhabha Atomic Research Center, Mumbai. The assembly technique includes material preparation in the lab (pre-assembly) and final detector assembly in the class-100 clean room. I participated in the assembly and quality control tests of eight chambers at Panjab University. All chambers passed quality control tests and have been installed in the CMS experiment. The physics analysis presented in this thesis is based on the measurement of the fiducial cross section for the production of a Z boson in association with at least one bottom quark jet. This is the first measurement of these processes based on data collected by the CMS experiment at a center-of-mass energy of 13 TeV during the 2016–18 data-taking period. The dataset corresponds to an integrated luminosity of 137 fb−1 . The Z + b-jets is a crucial process at the LHC for precision testing of electroweak and perturbative quantum chromodynamics (pQCD) calculations as it involves an electroweak and strong vertex in hadronic collisions. The b quark mass is above QCD scales so their production is not affected by low energy hadronization effects and is directly described by pQCD more precisely than a light-flavored jet. Understanding and modeling of pQCD interactions are important because they can affect the accuracy levels when we proceed with theoretical predictions. In pQCD, the amplitude for Z + b-jets processes can be computed using different parton distribution functions which provide information about the b quark content of the proton and also helps us to scrutinize the theoretical calculations by comparing predictions with experimental data. This comparison can help to improve the modeling of the production of b quarks. Furthermore, the Z + b-jets process constitutes an irreducible background to many SM and BSM physics processes that occur at hadron colliders, such as the production of Higgs bosons production in the HZ mode, the new generation of heavy quarks (b’, t’) decaying into Z + b-jets, supersymmetric Higgs bosons produced in association with b quarks, etc. This study may improve the purity and sensitivity of these relatively rare processes if one can measure and control the Z + b-jets process precisely enough, which can also help to constrain the theoretical modeling of data. Therefore, the study and understanding of the b-jets processes are very important to probe new physics and improve the precision of the measured properties of known processes and particles. The measurements Z+b-jets processes are performed with transverse momenta of the b-jets greater than 30 GeV and pseudorapidity |η| < 2.4. The integrated and differential cross sections are measured separately in the electron and muon decay channels and also in the combined channel. The differential cross section distributions are measured as functions of various kinematic observables which are sensi- tive to the b quark parton distribution function, pQCD calculations, initial-state-radiation, final-state-radiation, and multiple parton interactions. The detector-level distributions are corrected for the selection efficiencies or detector resolution effects and compared with different Monte Carlo event generators. It is observed that the measured fiducial cross sections and shapes of the kinematic observables are not completely described by all predictions.
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spelling cern-28662002023-08-16T15:19:06Zhttp://cds.cern.ch/record/2866200engMeena, MeenaStudy of Z + b-jets production at LHC energies using CMS detectorParticle Physics - ExperimentDetectors and Experimental TechniquesThe most successful theory in particle physics is the Standard Model (SM), which describes the fundamental particles and their interactions. The majority of SM predictions have been tested successfully with excellent precision. Despite its achievements, SM fails to resolve many key problems such as the inclusion of gravity, absence of dark matter, and unification of the gauge couplings at high energies, etc. Many scenarios beyond Standard Model (BSM) have been proposed to explain some of these aspects. To test the predictions of the SM and BSM scenarios several experiments have been designed and built. Among them, the Large Hadron Collider at the European Council for Nuclear Research is the largest and most powerful particle accelerator ever built. The proton beams are made to collide at four different locations along the LHC ring. At these positions, four giant detectors are placed to record every possible outcome of the collision. The Compact Muon Solenoid (CMS) is one of its general purpose detectors designed for SM measurements and BSM searches due to its high precision detection of particles from collision events. This thesis is based on two aspects: hardware work and physics analysis. This present work includes the assembly and testing of the Gas Electron Multiplier based GE1/1 subdetectors, which are used for the upgrade of the first endcap muon station of the CMS detector during the Long Shutdown2 period (December 2018–April 2022). The GE1/1 subdetectors have added redundancy to the muon subsystem of the CMS detector in the forward regions (higher η) and improved the triggering and muon tracks reconstruction capabilities. The GE1/1 chambers have an excellent detection efficiency of more than 97% with time and position resolution of 10 ns and 260 μm to 340 μm, respectively. The CMS GE1/1 upgrade project required the fabrication and testing of 144 GE1/1 chambers. India contributed to the CMS GE1/1 upgrade project, which included the assembly and testing of the GE1/1 chambers, which was carried out at Panjab University, Chandigarh, in collaboration with Delhi University, Delhi, and Bhabha Atomic Research Center, Mumbai. The assembly technique includes material preparation in the lab (pre-assembly) and final detector assembly in the class-100 clean room. I participated in the assembly and quality control tests of eight chambers at Panjab University. All chambers passed quality control tests and have been installed in the CMS experiment. The physics analysis presented in this thesis is based on the measurement of the fiducial cross section for the production of a Z boson in association with at least one bottom quark jet. This is the first measurement of these processes based on data collected by the CMS experiment at a center-of-mass energy of 13 TeV during the 2016–18 data-taking period. The dataset corresponds to an integrated luminosity of 137 fb−1 . The Z + b-jets is a crucial process at the LHC for precision testing of electroweak and perturbative quantum chromodynamics (pQCD) calculations as it involves an electroweak and strong vertex in hadronic collisions. The b quark mass is above QCD scales so their production is not affected by low energy hadronization effects and is directly described by pQCD more precisely than a light-flavored jet. Understanding and modeling of pQCD interactions are important because they can affect the accuracy levels when we proceed with theoretical predictions. In pQCD, the amplitude for Z + b-jets processes can be computed using different parton distribution functions which provide information about the b quark content of the proton and also helps us to scrutinize the theoretical calculations by comparing predictions with experimental data. This comparison can help to improve the modeling of the production of b quarks. Furthermore, the Z + b-jets process constitutes an irreducible background to many SM and BSM physics processes that occur at hadron colliders, such as the production of Higgs bosons production in the HZ mode, the new generation of heavy quarks (b’, t’) decaying into Z + b-jets, supersymmetric Higgs bosons produced in association with b quarks, etc. This study may improve the purity and sensitivity of these relatively rare processes if one can measure and control the Z + b-jets process precisely enough, which can also help to constrain the theoretical modeling of data. Therefore, the study and understanding of the b-jets processes are very important to probe new physics and improve the precision of the measured properties of known processes and particles. The measurements Z+b-jets processes are performed with transverse momenta of the b-jets greater than 30 GeV and pseudorapidity |η| < 2.4. The integrated and differential cross sections are measured separately in the electron and muon decay channels and also in the combined channel. The differential cross section distributions are measured as functions of various kinematic observables which are sensi- tive to the b quark parton distribution function, pQCD calculations, initial-state-radiation, final-state-radiation, and multiple parton interactions. The detector-level distributions are corrected for the selection efficiencies or detector resolution effects and compared with different Monte Carlo event generators. It is observed that the measured fiducial cross sections and shapes of the kinematic observables are not completely described by all predictions.CERN-THESIS-2022-375oai:cds.cern.ch:28662002023-07-28T10:35:53Z
spellingShingle Particle Physics - Experiment
Detectors and Experimental Techniques
Meena, Meena
Study of Z + b-jets production at LHC energies using CMS detector
title Study of Z + b-jets production at LHC energies using CMS detector
title_full Study of Z + b-jets production at LHC energies using CMS detector
title_fullStr Study of Z + b-jets production at LHC energies using CMS detector
title_full_unstemmed Study of Z + b-jets production at LHC energies using CMS detector
title_short Study of Z + b-jets production at LHC energies using CMS detector
title_sort study of z + b-jets production at lhc energies using cms detector
topic Particle Physics - Experiment
Detectors and Experimental Techniques
url http://cds.cern.ch/record/2866200
work_keys_str_mv AT meenameena studyofzbjetsproductionatlhcenergiesusingcmsdetector