Measurement of the elliptic anisotropy of charged particles produced in PbPb collisions at nucleon-nucleon center-of-mass energy = 2.76 TeV

TL;DR

This study measures the elliptic anisotropy of charged particles in PbPb collisions at 2.76 TeV using multiple methods, revealing a universal scaling with transverse particle density across energies and systems.

Contribution

It provides the first comprehensive measurement of elliptic anisotropy over a broad kinematic range at this energy, demonstrating a universal scaling behavior.

Findings

Elliptic anisotropy varies with transverse momentum and pseudorapidity.

Scaling with geometric eccentricity and particle density is observed.

Results are consistent with lower energy measurements and different collision systems.

Abstract

The anisotropy of the azimuthal distributions of charged particles produced in PbPb collisions with a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, two- and four-particle cumulants, and Lee--Yang zeros. The anisotropy is presented as a function of transverse momentum (pt), pseudorapidity (eta) over a broad kinematic range: 0.3 < pt < 20 GeV, abs(eta) < 2.4, and in 12 classes of collision centrality from 0 to 80%. The results are compared to those obtained at lower center-of-mass energies, and various scaling behaviors are examined. When scaled by the geometric eccentricity of the collision zone, the elliptic anisotropy is found to obey a universal scaling with the transverse particle density for different collision systems and center-of-mass energies.