Upcgen: a Monte Carlo simulation program for dilepton pair production in ultra-peripheral collisions of heavy ions

TL;DR

Upcgen is a Monte Carlo simulation tool for dilepton production in ultra-peripheral heavy-ion collisions, improving theoretical predictions and enabling studies of photon polarization and lepton magnetic moments.

Contribution

It introduces a refined photon flux treatment in Upcgen, enhancing agreement with experimental data and allowing new physics investigations.

Findings

Improved agreement with ATLAS dilepton data at large rapidities.

Enables study of photon polarization effects.

Allows setting of arbitrary lepton anomalous magnetic moments.

Abstract

Ultra-peripheral collisions (UPCs) of heavy ions can be used as a clean environment to study two-photon induced interactions such as dilepton pair photoproduction. Recently, precise data on lepton pair production in UPCs were obtained by the ATLAS experiment at the LHC where significant deviations, of up to 20%, from available theoretical predictions were observed. In this work, we present a Monte Carlo event generator, Upcgen, that implements a refined treatment of the photon flux allowing us to improve the agreement with ATLAS data at large dilepton rapidities. Besides, the new generator offers a possibility to study photon polarization effects and set arbitrary values of the lepton anomalous magnetic moment that can be used in the future studies of tau g-2 via ditau production measurements in UPCs.