# EPS-HEP2021 conference

26-30 July 2021
Zoom
Europe/Berlin timezone

## From Wigner distributions of photons to dilepton production in semicentral heavy ion collisions

29 Jul 2021, 16:45
15m
Zoom

#### Zoom

Parallel session talk Heavy Ion Physics

### Speaker

Mariola Kłusek-Gawenda (IInstitute of Nuclear Physics Polish Academy of Sciences)

### Description

Ultrarelativistic Heavy Ions of large charge Z are accompanied by a large flux of Weizsacker–Williams photons. This opens up the opportunity to study a variety of single photon induced nuclear processes, as well as photon-photon processes.

We would like to present a formalism which allows to calculate differential distributions of dileptons produced via photon-photon fusion in semi-central (impact parameter $<$ 2 $\times$ nuclear radius) nucleus-nucleus collisions for a given centrality. In this approach the differential cross section is calculated using the complete polarization density matrix of photons resulting from the Wigner distribution formalism. We will present several differential distributions such as invariant mass of dileptons, dilepton transverse momentum and acoplanarity for different regions of centrality. The results of the calculations will be compared to experimental data of the STAR, ALICE and ATLAS collaborations. Very good agreement with the data is achieved without free parameters in all cases. Additional final state rescattering of leptons in the quark-gluon plasma is not needed. Our new approach based on Wigner distributions of photons gives a much better agreement with experimental data than the previous approaches used in the literature.

M. Kłusek-Gawenda, W. Schaefer and A. Szczurek,
Centrality dependence of dilepton production via $\gamma \gamma$ processes from Wigner distributions of photons in nuclei,''
Phys. Lett. B814, 136114 (2021), [arXiv:2012.11973 [hep-ph]].

Collaboration / Activity Theory

### Primary authors

Mariola Kłusek-Gawenda (IInstitute of Nuclear Physics Polish Academy of Sciences) Antoni Szczurek (Institute of Nuclear Physics PAN, Krakow and Rzeszow University, Rzeszow) Wolfgang Schafer (Institute of Nuclear Physics Polish Academy of Sciences)