Systematics of azimuthal anisotropy harmonics in proton-nucleus collisions at the LHC from the Color Glass Condensate

TL;DR

This paper investigates azimuthal anisotropy harmonics in proton-nucleus collisions at the LHC using the Color Glass Condensate framework, confirming theoretical predictions with experimental data and highlighting the framework's effectiveness.

Contribution

The study provides the first systematic comparison of CGC predictions with LHC data for azimuthal harmonics, validating power counting expectations for v_2, v_3, and v_4.

Findings

Qualitative and quantitative agreement of v_2 and v_4 with CGC predictions.

Excellent qualitative match of v_3 data with theoretical expectations.

Highlights the CGC framework's predictive power for small system collisions.

Abstract

Simple power counting arguments in the dilute-dense framework of the Color Glass Condensate (CGC) Effective Field Theory predict that even and odd azimuthal anisotropy harmonics of two-particle correlations in proton-nucleus collisions at the LHC will respectively satisfy v^2_{2n} ~ N_{ch}^0 and v^2_{2n+1} ~ N_{ch}, where N_{ch} denotes the number of charged particles. We show that these expectations are borne out qualitatively, and even quantitatively, within systematic uncertainties, for v_2 and v_4 in comparisons with data from the ATLAS collaboration. We also observe that ATLAS data for the v_3 azimuthal harmonic are in excellent agreement with our qualitative expectation; quantitative comparisons are numerically challenging at present. The lessons from this study fully complement those gained by the recent comparison of the CGC dilute-dense framework [arXiv:1805.09342] to data from the PHENIX collaboration on small system collisions at RHIC.