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

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 sqrts=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 ϕ_η ^⁎ 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 ϕ_η ^⁎ 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.