Z Boson Cross Section Measurements and Neutral Higgs Boson Search in the Di-muon Channel with the CMS Detector


Book Description

In this thesis, measurements of inclusive and differential Z boson production cross sections in proton-proton collisions at [square root of] s =13 TeV with the CMS detector at Large Hadron Collider are performed with the di-muon channel. The measured total inclusive cross section times branching ratio is or(pp - ZX) x [beta](Z --> [mu][mu]) = 1870 ± 2(stat) ± 35(syst) ± 51(lumi) pb for the di-muon invariant mass in the range of 60 to 120 GeV, which is in good agreement with the next-to-next-to leading order QCD predictions. The spectra of Z boson transverse momentum, ... variable, rapidity, and the muon transverse momentum are also measured and compared with theoretical predictions. The large production cross section of Z boson and good experimental accessibility of final-state muons permit a real-time monitoring of luminosities using the counts of reconstructed Z --> [mu][mu] events. Preliminary results of counting of Z bosons as a luminometer are shown using the entire 2018 data-taking period. A search for beyond Standard Model neutral Higgs bosons decaying to two muons is also presented. No significant excess is observed. A 95% confidence level upper limit is set on ... The exclusion contour is also determined on the parameter phase space in the context of Minimal Supersymmetric Standard Mode representative benchmark scenarios.




Search for the Standard Model Higgs Boson in the Z Gamma Channel


Book Description

The Higgs decay into a photon and a Z boson, with the Z boson decaying into an electron-positron pair (electron channel) or muon-antimuon pair (muon channel), allows for accurate reconstructions of the Higgs boson mass and measurement of the Higgs to Z-[gamma] coupling. We explore selection criteria for the photon and the two leptons and provide preliminary observed and expected limits for the Higgs boson production cross section in the mass range from 120 GeV to 150 GeV. The data used in this analysis was collected with the CMS detector and corresponds to 5 fb- 1 and 19 fb-1 at center-of-mass energies of 7 TeV and 8 TeV, respectively.




Observation of a New State in the Search for the Higgs Boson at CMS


Book Description

This book describes the searches that lead to the discovery of a Higgs boson performed at CMS, one of the two main experiments at the CERN LHC. After an overview of the theory and of the CMS experiment, all search channels are described, with emphasis on the ones with the best sensitivity. The statistical methodology used to analyse and the outcomes of the searches and the discovery results are then presented in detail.




Search for the Higgs Boson in the Vector Boson Fusion Channel at the ATLAS Detector


Book Description

This Thesis describes the first measurement of, and constraints on, Higgs boson production in the vector boson fusion mode, where the Higgs decays to b quarks (the most common decay channel), at the LHC. The vector boson fusion mode, in which the Higgs is produced simultaneously with a pair of quark jets, provides an unparalleled opportunity to study the detailed properties of the Higgs, including the possibility of parity and CP violation, as well as its couplings and mass. It thus opens up this new field of study for precision investigation as the LHC increases in energy and intensity, leading the way to this new and exciting arena of precision Higgs research.




The Search and Discovery of the Higgs Boson


Book Description

This book provides a general description of the search for and discovery of the Higgs boson (particle) at CERN’s Large Hadron Collider. The goal is to provide a relatively brief overview of the issues, instruments and techniques relevant for this search; written by a physicist who was directly involved. The Higgs boson mat be the one particle that was studied the most before its discovery and the story from postulation in 1964 to detection in 2012 is a fascinating one. The story is told here while detailing the fundamentals of particle physics.




Discovery and Measurement of the Higgs Boson in the WW Decay Channel


Book Description

This thesis describes the stand-alone discovery and measurement of the Higgs boson in its decays to two W bosons using the Run-I ATLAS dataset. This is the most precise measurement of gluon-fusion Higgs boson production and is among the most significant results attained at the LHC. The thesis provides an exceptionally clear exposition on a complicated analysis performed by a large team of researchers. Aspects of the analysis performed by the author are explained in detail; these include new methods for evaluating uncertainties on the jet binning used in the analysis and for estimating the background due to associated production of a W boson and an off-shell photon. The thesis also describes a measurement of the WW cross section, an essential background to Higgs boson production. The primary motivation of the LHC was to prove or disprove the existence of the Higgs boson. In 2012, CERN announced this discovery and the resultant ATLAS publication contained three decay channels: gg, ZZ, and WW.




A Beauty-ful Boson


Book Description

The analysis described in this thesis is the search for the Higgs boson, decaying into bb pair, in the associated production with a vector boson, in the extreme Higgs boson transverse momentum region where the Higgs boson is reconstructed using the large-R jet technique. The use of the large-R jets allows to add a part of the phase space unexplored so far, which is particularly sensitive to possible new physics. The analysed data have been collected at LHC by the ATLAS detector between 2015 and 2018 at a centre-of-mass energy of √s = 13 TeV. The same dataset has been used to perform the differential pp → ZH and pp → WH cross-section measurements used to extract the information on the Higgs couplings and to put limits on Beyond the Standard Model effects. Furthermore the analysis has been re-used to perform a cross-section measurement of the diboson ZZ and WZ processes because the diboson and the Higgs processes have a similar topology. For the first time the ZZ(bb) and WZ(bb) cross-sections are measured at √s = 13 TeV and the observed cross-section measurements are consistent with the Standard Model predictions.




Measurement of W + Bb̄ and a Search for MSSM Higgs Bosons with the CMS Detector at the LHC


Book Description

This thesis describes a Standard Model (SM) cross section measurement of W+bb as well as a search for neutral Higgs bosons in the Minimal Supersymmetric Extension of the Standard Model (MSSM) decaying to tau pairs. The measurement of W+bb was performed using proton-proton collisions at sqrt(s) = 7 TeV in a data sample collected with the CMS experiment at the LHC corresponding to an integrated luminosity of 5.0 1/fb. The W+bb events are selected in the W to muon + neutrino decay mode by requiring a muon with transverse momentum pT>25 GeV and pseudorapidity absolute eta less than 2.1, and exactly two b-tagged jets with pT>25 GeV and absolute eta less than 2.4. The measured W+bb production cross section in the fiducial region, calculated at the level of final-state particles, is 0.53± 0.05(stat.) ± 0.09 (syst.) ± 0.06 (theory) ± 0.01 (lum.) pb, in agreement with the SM prediction. This measurement is a sensitive test of heavy quark production calculated with perturbative QCD. It also serves as an important benchmark in new physics searches which include a single isolated lepton and one or more b jets in the final state, as W+bb becomes an irreducible background. Also presented is a search for the CP-even MSSM Higgs bosons, H and h, and the CP-odd MSSM pseudoscalar, A, in their decays to tau pairs. This search is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012 at a center-of-mass energy of 7 TeV and 8 TeV respectively. The dataset corresponds to an integrated luminosity of 24.6 1/fb, with 4.9 1/fb at 7 TeV and 19.7 1/fb at 8 TeV. To enhance the sensitivity to neutral MSSM Higgs bosons, the search includes the case where the Higgs boson is produced in association with a b-quark jet. No excess is observed in the tau-pair invariant-mass spectrum.




The Standard Model Higgs Boson


Book Description

Volume 8.