Dilepton emission as a novel probe of QCD critical point

TL;DR

This paper proposes dilepton emission rate as a novel and sensitive probe for locating the QCD critical point, linking theoretical predictions with potential experimental measurements in heavy ion collisions.

Contribution

It introduces a model-based approach to connect dilepton emission rates with chiral symmetry and criticality, providing a new method to identify the QCD critical point.

Findings

DER peaks reflect chiral transition and criticality.

DER fluctuations are more sensitive than baryon number fluctuations.

Baseline subtracted DER highlights critical fluctuations.

Abstract

In this work, we propose dilepton emission rate (DER) as a sensitive probe of QCD critical point based on the extended Polyakov-quark-meson model. The model could successfully capture two main mechanisms for dilepton production, $\pi^\pm$ and quark-antiquark annihilations on one hand, and self-consistently account for chiral transition and (de-)confinement on the other hand. Along the chemical freezeout lines, all the moments of the DER peak show similar extremal features as those of light quark mass, thus the DER can well reflect the change of chiral symmetry and criticality. More importantly, the DER can be directly measured in heavy ion collisions: Compared to the baryon number fluctuations, the DER fluctuations are found to be more drastic in the critical region and more sensitive to the relative location of the critical point. However, recent statistics of DER in heavy ion collision is not large enough to perform event-by-event measurement, instead we propose to study the baseline subtracted DER: For a given dilepton center of mass, the largest deviation shows up around the point where the light quark mass fluctuation is the strongest.