Measurement Of The Boson Z Differential Cross Section In Transverse Momentum In The Electron Positron Channel With The Atlas Detector At Lhc

"This thesis presents the results of two measurements of the Z boson, one of the mediators of the electroweak force in the Standard Model of particle physics. The first is the measurement of the total and the differential production cross-sections of the Z boson, and the second is the determination of the spin of the particle. The measurements are made with the 6.1 fb-1 proton-proton collision data collected by the ATLAS detector in 2016 at a center of mass energy of 13 TeV with the Large Hadron Collider. The leptonic decay of the Z boson into an electron-positron pair is the channel examined. The measurements are compared with the theoretical predictions at next-to-leading order for a quantitative and a precise understanding of the process. The observed results agree with the Standard Model expectations within uncertainties. The total cross-section of Z production in the di-electron channel is measured to be 1.878 ± 0.02 (stat)_(−0.052)^(+0.045) (syst) ± 0.042 (lumi) nb and the differential cross-sections as functions of the transverse momentum and the rapidity of the Z particle match with the predictions. The angular distribution of the electrons confirms the spin 1 nature of the Z boson, also in accordance with the Standard Model." --

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.

We report measurements of differential production cross-sections of a Z boson in association with b-jets in pp collisions at √ s = 7 TeV. The data analysed correspond to an integrated luminosity of 4.6 fb-1 recorded with the ATLAS detector at the Large Hadron Collider. Particle-level cross-sections are determined for events with a Z boson decaying into an electron or muon pair, and containing b-jets. For events with at least one b-jet, the cross-section is presented as a function of the Z boson transverse momentum and rapidity, together with the inclusive b-jet cross-section as a function of b-jet transverse momentum, rapidity and angular separations between the b-jet and the Z boson. For events with at least two b-jets, the cross-section is determined as a function of the invariant mass and angular separation of the two highest transverse momentum b-jets, and as a function of the Z boson transverse momentum and rapidity. Lastly, results are compared to leading-order and next-to-leading-order perturbative QCD calculations.

We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy √s=8 TeV, corresponding to an integrated luminosity of 19.7 fb-1. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the fewz program. The results are also compared to the commonly used leading-order MadGraph and next-to-leading-order powheg generators.

In this study, the ratio of the production cross sections for W and Z bosons in association with jets has been measured in proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider. The measurement is based on the entire 2011 dataset, corresponding to an integrated luminosity of 4.6 fb-1. Inclusive and differential cross-section ratios for massive vector bosons decaying to electrons and muons are measured in association with jets with transverse momentum pT > 30 GeV and jet rapidity.

The first part of this thesis presents the measurement of the inclusive cross-section for electron production from heavy-flavour decays in the electron transverse momentum range 7 GeV

This paper presents cross sections for the production of a W boson in association with jets, measured in proton-proton collisions at \(\sqrt{s} = 7\) TeV with the ATLAS experiment at the large hadron collider. With an integrated luminosity of 4.6fb-1, this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of 1TeV and multiplicities up to seven associated jets. The production cross sections for W bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. As a result, the measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators.

Integrated fiducial cross sections for the production of four leptons via the H → 4l decays (l = e, [mu]) are measured in pp collisions at $ \sqrt{s}=7 $ and 8TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 fb$^{-1}$ at 7TeV, and 19.7 fb$^{-1}$ at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are measured using the 8 TeV data, and are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z → 4l cross section, and its ratio to the H → 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. Here, the integrated H → 4l fiducial cross section is measured to be 0.56$_{-0.44}^{+0.67}$ (stat)$_{-0.06}^{+0.21}$ (syst) fb at 7 TeV, and 1.11$_{-0.35}^{+0.41}$ (stat)$_{-0.10}^{+0.14}$ (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.

Here, this paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the H → WW *→ e??? channel, using 20.3 fb–1 of proton-proton collision data. The data were produced at a centre-of-mass energy of √s = 8 TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed H→ W W*→ e??? signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.