Measurement of Z boson Production in Lead-Lead Collisions at $\sqrt{s_{NN}}$ 2.76 TeV with the ATLAS Detector

TL;DR

This paper reports the measurement of Z boson production in lead-lead collisions at 2.76 TeV using the ATLAS detector, demonstrating that Z boson yield scales with binary collision estimates and shows no elliptic flow.

Contribution

First measurement of Z boson production in Pb+Pb collisions at 2.76 TeV with detailed analysis of yield and azimuthal distribution.

Findings

Z boson yield proportional to binary collision number

Background contamination less than 3%

Elliptic flow coefficient consistent with zero

Abstract

The ATLAS experiment has observed 1995 $Z$ boson candidates in 0.15 nb$^{-1}$ of integrated luminosity obtained in the 2011 LHC Pb+Pb run at $\sqrt{s_{NN}}$ 2.76 TeV. The $Z$ bosons are reconstructed via di-electron and di-muon decay channels. The results from both channels are consistent with each other and are combined. The background is less than 3% of the selected sample. Within the statistical and systematic uncertainties, the per-event $Z$ boson yield integrated over rapidity $|y^{Z}|<2.5$ is proportional to the number of binary collisions estimated by the Glauber model. The elliptic flow coefficient of the azimuthal distribution of the $Z$ boson with respect to the event plane is consistent with zero.