Measurement of the W, Z and photon production in lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS detector

TL;DR

This paper reports on the measurement of W, Z, and photon production in lead-lead collisions at 2.76 TeV, showing yields scale with nucleon-nucleon collisions and distributions are consistent across centralities.

Contribution

First measurement of W, Z, and photon yields in Pb+Pb collisions at 2.76 TeV with detailed distribution analysis and comparison to models.

Findings

Yields scale with number of nucleon-nucleon collisions.

Distributions do not change shape with centrality.

Z boson distributions match Pythia model predictions.

Abstract

The ATLAS experiment measures yields of isolated photons and of Z and W bosons via leptonic decay modes in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV. The data samples used in the analysis were obtained in the year 2010 and year 2011 LHC runs and correspond to 5 ub-1 and 0.15 nb-1 of integrated luminosity respectively. The measured yields of all bosons are consistent with the scaling proportional to the number of nucleon-nucleon collisions. The transverse momentum distributions are measured for isolated photons and for Z bosons for different centrality bins. The shapes of measured distributions do not change with centrality. The transverse momentum and rapidity distributions of Z boson are consistent in shape with Pythia model and the second harmonic coefficient of the azimuthal distribution of Z bosons with respect to the event plane is consistent with zero.