Measurement of angular correlations in Drell-Yan lepton pairs to probe Z/gamma* boson transverse momentum at sqrt(s)=7 TeV with the ATLAS detector

TL;DR

This paper presents a precise measurement of angular correlations in Drell-Yan lepton pairs using the phistar observable at 7 TeV, providing insights into Z boson transverse momentum with improved experimental resolution.

Contribution

It introduces the use of the phistar observable to probe Z boson transverse momentum with better resolution and combines electron and muon channels for enhanced accuracy.

Findings

Data are well described by resummed QCD predictions.

Measurement precision exceeds current theoretical uncertainties by an order of magnitude.

Monte Carlo generators can also accurately model the data.

Abstract

A measurement of angular correlations in Drell-Yan lepton pairs via the phistar observable is presented. This variable probes the same physics as the Z/gamma* boson transverse momentum with a better experimental resolution. The Z/gamma*->e+e- and Z/gamma*->mu+mu- decays produced in proton--proton collisions at a centre-of-mass energy of sqrt(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 phistar 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 phistar 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. Some of the Monte Carlo event generators are also able to describe the data. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties.