Measurement of angular correlations in Drell–Yan lepton pairs to probe 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
√
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
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.