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"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 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.
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.
This thesis reports on the measurement of the W and Z boson inclusive production cross sections ([sigma][sub W] and[sigma][sub Z]) times electronic branching ratios (Br(W[r-arrow] e[nu]) and Br(Z[r-arrow] ee)) in p[anti p] collisions at[radical]s= 1.8 TeV. The analysis is based on 12.8 pb[sup[minus]1] of data taken in the 1992--1993 run by the D0 detector at the Fermilab Tevatron collider; the cross sections were measured to be:[sigma][sub W][center-dot] Br(W[r-arrow] e[nu])= 2.36[+-] 0.02[+-] 0.07[+-] 0.13 nb and[sigma][sub Z][center-dot] Br(Z[r-arrow] ee)= 0.218[+-] 0.008[+-] 0.008[+-] 0.012 nb. The first error is statistical, the second error represents the non-luminosity systematic error, and the third error shows the uncertainty in the luminosity determination. Future prospects for similar measurements based on larger samples of data are discussed.
The ZZ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb–1 of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66–116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for Z bosons in the same mass range and of all decay modes, giving 16.7+2.2–2.0(stat)+0.9–0.7(syst)+1.0–0.7(lumi) pb. Lastly, the results agree with standard model predictions.
This thesis reports on the measurement of the W and Z boson inclusive production cross sections (?{sub W} and?{sub Z}) times electronic branching ratios (Br(W → e?) and Br(Z → ee)) in p{anti p} collisions at √s = 1.8 TeV. The analysis is based on 12.8 pb{sup −1} of data taken in the 1992--1993 run by the D0 detector at the Fermilab Tevatron collider; the cross sections were measured to be:?{sub W} · Br(W → e?) = 2.36 ± 0.02 ± 0.07 ± 0.13 nb and?{sub Z} · Br(Z → ee) = 0.218 ± 0.008 ± 0.008 ± 0.012 nb. The first error is statistical, the second error represents the non-luminosity systematic error, and the third error shows the uncertainty in the luminosity determination. Future prospects for similar measurements based on larger samples of data are discussed.