Measurement of the centrality and pseudorapidity dependence of the integrated elliptic flow in lead-lead collisions at sqrt(s_NN)=2.76 TeV with the ATLAS detector

TL;DR

This paper measures the integrated elliptic flow of charged particles in lead-lead collisions at 2.76 TeV using the ATLAS detector, analyzing its dependence on pseudorapidity and collision centrality to understand the collision dynamics.

Contribution

It provides the first measurement of the integrated elliptic flow over a broad pseudorapidity range at LHC energies, including low transverse momentum tracks, and compares results with lower-energy RHIC data.

Findings

Weak pseudorapidity dependence of v2 in central collisions

Small decrease in v2 away from mid-rapidity in peripheral collisions

Comparison of v2 in the rest frame with RHIC data

Abstract

The integrated elliptic flow of charged particles produced in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV has been measured with the ATLAS detector using data collected at the Large Hadron Collider. The anisotropy parameter, v_2, was measured in the pseudorapidity range |eta| <= 2.5 with the event-plane method. In order to include tracks with very low transverse momentum pT, thus reducing the uncertainty in v_2 integrated over pT, a 1 mu b-1 data sample without a magnetic field in the tracking detectors is used. The centrality dependence of the integrated v_2 is compared to other measurements obtained with higher pT thresholds. A weak pseudorapidity dependence of the integrated elliptic flow is observed for central collisions, and a small decrease when moving away from mid-rapidity is observed only in peripheral collisions. The integrated v2 transformed to the rest frame of one of the colliding nuclei is compared to the lower-energy RHIC data.