Medium-modified Jets and Initial State Fluctuations as Sources of Charge Correlations Measured at RHIC

TL;DR

This paper explores how medium-modified jets and initial state fluctuations contribute to charge asymmetries in heavy ion collisions at RHIC, finding initial fluctuations can qualitatively match observed asymmetries.

Contribution

It combines jet energy loss modeling with event-by-event hydrodynamics to assess initial state effects on charge correlations, highlighting the role of fluctuations.

Findings

Initial state fluctuations can produce charge asymmetries similar to experimental observations.

Jet production probabilities are too small to significantly influence charge asymmetries.

Multi-particle correlations can help distinguish different sources of asymmetry, but are affected by resonance decay subtraction.

Abstract

We investigate the contribution of medium-modified jets and initial state fluctuations to the asymmetry in charged particle production with respect to the reaction plane. This asymmetry has been suggested as a compelling signature of the Chiral Magnetic Effect in QCD and make a study of "conventional" scenarios for the creation of such charged particle multiplicity fluctuations a timely endeavor. The different pathlength combinations of jets through the medium in non-central heavy ion collisions result in finite correlations of like and different charged particles emitted in the different hemispheres. Our calculation is based on combining jet events from YaJEM (Yet another Jet Energy Loss Model) and a bulk medium evolution. It is found that the jet production probabilities are too small to observe this effect. The influence of initial state fluctuations on this observable is explored using an event-by-event (3+1)d hybrid approach that is based on UrQMD (Ultra-relativistic Quantum Molecular Dynamics) with an ideal hydrodynamic evolution. In this calculation momentum conservation and elliptic flow are explicitly taken into account. The asymmetries in the initial state are translated to a final state momentum asymmetry by the hydrodynamic flow profile. Dependent on the size of the initial state fluctuations the resulting charged particle asymmetries are in qualitative agreement with the preliminary STAR results. The multi-particle correlation as proposed by the PHENIX collaboration can in principle be used to disentangle the different contributions, however is in practice substantially affected by the procedure to subtract trivial resonance decay contributions.