Azimuth Quadrupole Systematics in Au-Au Collisions

TL;DR

This paper measures azimuthal quadrupole correlations in Au-Au collisions at different energies and centralities, revealing universal features and providing a detailed parametrization of the $v_2$ spectra.

Contribution

It introduces a method to isolate the azimuth quadrupole component from two-particle correlations and characterizes its $p_t$ spectra across centralities and energies.

Findings

Quadrupole $p_t$ spectra are described by a fixed boost and universal Lévý form.

A factorization of $v_2$ dependence into centrality and $p_t$ components is demonstrated.

Results are consistent with model predictions and previous measurements.

Abstract

We have measured $p_t$-dependent two-particle number correlations on azimuth and pseudorapidity for eleven centralities of $\sqrt{s_{NN}} = 62$ and 200~GeV Au-Au collisions at STAR. 2D fits to these angular correlations isolate the azimuth quadrupole amplitude, denoted $2 v_2^2 \{ 2D \} ( p_t )$, from localized same-side correlations. Event-plane $v_2 ( p_t )$ measurements within the STAR TPC acceptance can be expressed as a sum of the azimuth quadrupole and the quadrupole component of the same-side peak. $v_2 \{ 2D \} ( p_t )$ can be transformed to reveal quadrupole $p_t$ spectra which are approximately described by a fixed transverse boost and universal L\'evy form nearly independent of centrality. A parametrization of $v_2 \{ 2D \} ( p_t )$ can be factored into centrality and $p_t$-dependent pieces with a simple $p_t$ dependence above 0.75 GeV/c. Results from STAR are compared to published data and model predictions.