UPC2025: The second international workshop on the physics of Ultra Peripheral Collisions

Session

Monte Carlo event generators for UPCs and photon-mediated processes

11 Jun 2025, 09:40

Saariselkä, Finland

23. Recent development on gamma gamma collisions at hadron colliders

Nicolas Crépet (IJCLab)

11/06/2025, 09:40

Monte Carlo event generators for UPCs and photon-mediated processes

The LHC is not only the energy-frontier collider for parton-parton collisions, but it has proven to work as a powerful photon collider providing photon-photon collisions at center-of-mass energies never reached before. I will present results of the gamma-UPC Monte Carlo event generator [1] that can calculate any arbitrary exclusive final states produced via photon fusion in ultraperipheral...

94. Upcgen: An event generator for dilepton pair production in UPCs

Paul Alois Buhler (Stefan Meyer Institute for Subatomic Physics (SMI), Austrian Academy of Sciences (AT))

11/06/2025, 10:00

Monte Carlo event generators for UPCs and photon-mediated processes

We present Upcgen, a Monte Carlo event generator designed for simulating dilepton pair production in ultra-peripheral collisions (UPCs) [1]. In Upcgen the dilepton pair production cross section A+A -> A+A + ll is calculated by folding the elementary gamma gamma -> ll cross section with the two-photon luminosity produced by the colliding nuclei. The calculation of the two-photon luminosity is...

38. The STARlight Monte Carlo Event Generator

Janet Elizabeth Seger (Creighton University (US)), Prof. Janet Seger (Creighton University (US))

11/06/2025, 11:00

Monte Carlo event generators for UPCs and photon-mediated processes

The STARlight Monte Carlo event generator was developed more than 20 years ago and has been used extensively for the study of ultra-peripheral relativistic heavy ion collisions ever since.
STARlight can calculate cross sections for the two-photon production of dilepton pairs and single mesons and for both coherent and incoherent photonuclear production of vector mesons. The photon spectrum...

52. Dijet Photoproduction in POWHEG-Box

Alexander Feike (University of Münster)

11/06/2025, 11:20

Monte Carlo event generators for UPCs and photon-mediated processes

Photoproduction processes have gained a renewed interest following the approval of the EIC, making their implementation in Monte Carlo event generators highly desirable. I will present recent efforts to develop a POWHEG-BOX extension simulating dijet production from direct and resolved photons at NLO, leveraging the Weizsäcker-Williams Approximation. Its wide-ranging applicability will enable...

31. MC@NLO for UPCs in Sherpa

Peter Meinzinger (Zürich University)

11/06/2025, 11:40

Monte Carlo event generators for UPCs and photon-mediated processes

We discuss recent developments in the Sherpa event generator with regard to UPCs. Different form factors for the photon flux for both protons and heavy nuclei are compared and finite size effects of the emitters are taken into account. We present preliminary results for jet prodcution at NLO matched to the parton shower using MC@NLO, as well as NLO QED calculations for exclusive muon-pair...

50. Photo-nuclear collisions in Pythia 8

Dr Ilkka Helenius (University of Jyväskylä)

11/06/2025, 12:00

Monte Carlo event generators for UPCs and photon-mediated processes

We present the recent developments in simulations of ultra-peripheral collisions with the Pythia 8 Monte Carlo event generator. We first review the status of recent comparisons and tuning efforts to HERA photoproduction data which provide the baseline of photon-nucleon interactions. Then we present the vector-meson-dominance (VMD) based approach to model interactions between a real photon and...

66. Describing UPC data with the Sartre event generator

Tobias Toll, Vaidehi Nattoja (Indian Institute of Technology, Delhi)

11/06/2025, 12:20

Monte Carlo event generators for UPCs and photon-mediated processes

We present a comprehensive comparison with the Sartre event generator and available exclusive diffraction data from UPC of heavy ions. Sartre now takes all phenomena unique to UPC into account, i.e. interference effects, neutron emissions due to secondary and tertiary photon interactions, as well as a photon pt, paired with a reliable saturated small-x QCD model (IPSat). This enables us to use...

26. LbLatNLO: light-by-light at NLO

AJJATH ABDUL HAMEED (IPPP, Durham)

Monte Carlo event generators for UPCs and photon-mediated processes

In this talk I plan to discuss the next to leading order corrections to light by light scattering process in QCD+QED. Recent experimental observation of this fundamental process in ultra peripheral collision at LHC has revived the interest to precisely predict its cross-section. We discuss
two radically different computational approaches, both exact in the fermion mass dependence,...