Estimate of the CME signal in heavy-ion collisions from measurements relative to the participant and spectator flow planes

TL;DR

This paper discusses a strategy to better estimate the Chiral Magnetic Effect signal in heavy-ion collisions by comparing measurements relative to participant and spectator flow planes, aiming to reduce background effects.

Contribution

It proposes a new experimental approach to distinguish CME signals from background by analyzing flow plane dependencies and evaluates assumptions for this method.

Findings

Background contribution scales with elliptic flow $v_2$

Measurements relative to spectator plane may enhance CME signal detection

Strategy could improve separation of CME signal from background

Abstract

An interpretation of the charge dependent correlations sensitive to the Chiral Magnetic Effect (CME) -- the separation of the electric charges along the system magnetic field (across the reaction plane) -- is ambiguous due to a possible large background (non-CME) effects. The background contribution is proportional to the elliptic flow $v_2$; it is the largest in measurements relative to the participant plane, and is smaller in measurements relative to the flow plane determined by spectators, where the CME signal, on opposite, is likely larger. In this note I discuss a possible strategy for corresponding experimental measurements, and list and evaluate different assumptions related to this approach.