Lighting up the Photon Wigner Distribution via Dilepton Productions

TL;DR

This paper develops a unified framework using the Wigner photon distribution to describe dilepton production in heavy-ion collisions, integrating coherent and incoherent photon contributions and matching experimental data from RHIC to LHC.

Contribution

It introduces a comprehensive factorization formula for dilepton production based on the photon Wigner distribution, including novel predictions for anisotropies and sub-structure contributions.

Findings

The framework accurately describes RHIC and LHC dilepton data.

Photon radiation includes both coherent and incoherent contributions.

Predictions for anisotropies in dilepton correlations are provided.

Abstract

We present a systematic investigation of lepton pair production through photon-photon fusion processes in heavy-ion collisions. It is demonstrated that the dilepton production at a given impact parameter ($b_\perp$) with a fixed transverse momentum imbalance ($q_\perp$) can be factorized into a unified formula in terms of the Wigner photon distribution of heavy nuclei. We show that this framework provides a comprehensive description of all the relevant data from RHIC to the LHC, with a strong evidence that the quasi-real photon can be radiated not only from the nucleus as a whole, standing for the coherent contribution, but also from the sub-structures inside the nucleus, representing the incoherent contribution. Further predictions are made for the anisotropies in the correlations between $q_\perp$, $b_\perp$, and the dilepton transverse momentum ($P_\perp$). This will help us to constrain the photon Wigner distribution which plays a crucial role to study the gluonic matter of nucleus at small-$x$ through the diffractive photoproduction processes in heavy ion collision.