Abstract
The production cross-sections for W^{pm } and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb^{-1} collected at a centre-of-mass energy sqrt{s}=2.76 TeV. The decay channels W rightarrow ell nu and Z rightarrow ell ell are used, where ell can be an electron or a muon. The cross-sections are presented for a fiducial region defined by the detector acceptance and are also extrapolated to the full phase space for the total inclusive production cross-section. The combined (average) total inclusive cross-sections for the electron and muon channels are: σW+→ℓνtot=2312±26(stat.)±27(syst.)±72(lumi.)±30(extr.)pb,σW-→ℓνtot=1399±21(stat.)±17(syst.)±43(lumi.)±21(extr.)pb,σZ→ℓℓtot=323.4±9.8(stat.)±5.0(syst.)±10.0(lumi.)±5.5(extr.)pb.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$\\begin{aligned} \\sigma ^{\\text {tot}}_{W^{+}\\rightarrow \\ell \\nu }= & {} 2312 \\pm 26\\ (\\text {stat.})\\\\&\\pm 27\\ (\\text {syst.}) \\pm 72\\ (\\text {lumi.}) \\pm 30\\ (\\text {extr.})~\\text {pb} , \\\\ \\sigma ^{\\text {tot}}_{W^{-}\\rightarrow \\ell \\nu }= & {} 1399 \\pm 21\\ (\\text {stat.})\\ \\pm 17\\ (\\text {syst.}) \\\\&\\pm 43\\ (\\text {lumi.}) \\pm 21\\ (\\text {extr.})~\\text {pb} , \\\\ \\sigma ^{\\text {tot}}_{Z \\rightarrow \\ell \\ell }= & {} 323.4 \\pm 9.8\\ (\\text {stat.}) \\pm 5.0\\ (\\text {syst.})\\\\&\\pm 10.0\\ (\\text {lumi.}) \\pm 5.5 (\\text {extr.}) ~\\text {pb} . \\end{aligned}$$\\end{document}Measured ratios and asymmetries constructed using these cross-sections are also presented. These observables benefit from full or partial cancellation of many systematic uncertainties that are correlated between the different measurements.
Highlights
Background samplesW → τν Z → τ+τ− t t WW ZZ WZ bbcc GeneratorPowheg- Box +Pythia 8 Powheg- Box +Pythia 8Powheg- Box +Pythia 8 Powheg- Box +Pythia 8 Powheg- Box +Pythia 6 Herwig Herwig Herwig Pythia 8 Pythia 8Generator QCD precision next-to-leading order (NLO) NLONLO NLO NLO LO LO LO LO LO that used in the recent ATLAS measurement of the W -boson mass [60], first correcting the modelling of the overall recoil in simulation and applying corrections for residual differences in the recoil response and resolution that are derived from Z -boson data and transferred to the W -boson sample.The W -boson selection requires events to contain exactly one lepton candidate and haveETmiss > 25 GeV
The background processes that contribute to the sample of events passing the W -boson and Z -boson selections can be separated into two categories: those estimated from Monte Carlo (MC) simulation and theoretical calculations, and those estimated directly from data
The main backgrounds that contribute to the event sample passing the W -boson selection are processes with a τ -lepton decaying into an electron or muon plus neutrinos, leptonic Z -boson decays where only one lepton is reconstructed, and multijet processes
Summary
The ATLAS detector [34] at the LHC covers nearly the entire solid angle around the collision point It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic (EM) and hadronic calorimeters, and a muon spectrometer (MS) incorporating three large superconducting toroid magnets. The high-granularity silicon pixel detector covers the vertex region and typically provides three measurements per track It is followed by the silicon microstrip tracker, which usually provides eight measurements from eight strip layers. Within the region |η| < 3.2, EM calorimetry is provided by barrel and endcap high-granularity lead/liquidargon (LAr) sampling calorimeters, with an additional thin LAr presampler covering |η| < 1.8 that is used to correct for energy loss in material upstream of the calorimeters. This was followed by two software-based triggers that together reduced the event rate to about 200 Hz
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