Measurement of angular correlations in Drell–Yan lepton pairs to probe Z/γ ∗ boson transverse momentum at √s = 7 TeV with the ATLAS detector

Abstract

A measurement of angular correlations in Drell–Yan lepton pairs via the φ∗ η observable is presented. This variable probes the same physics as the Z/γ ∗ boson transverse momentum with a better experimental resolution. The Z/γ ∗ → e+e− and Z/γ ∗ → μ+μ− decays produced in proton–proton collisions at a centre-of-mass energy of √s = 7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb−1. Normalised differential cross sections as a function of <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mrow is="true"><mi is="true">ϕ</mi></mrow><mrow is="true"><mi is="true">η</mi></mrow> <mrow is="true"><mo is="true">⁎</mo></mrow></msubsup></math> are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is also measured double differentially as a function of <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mrow is="true"> <mi is="true">ϕ</mi></mrow><mrow is="true"><mi is="true">η</mi></mrow> <mrow is="true"><mo is="true">⁎</mo></mrow></msubsup></math> for three independent bins of the Z boson rapidity. The results are compared to QCD calculations and to predictions from different Monte Carlo event generators. The data are reasonably well described, in all measured Z boson rapidity regions, by resummed QCD predictions combined with fixed-order perturbative QCD calculations or by some Monte Carlo event generators. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties.