Inclusive vs Exclusive Ultra-Peripheral Collisions at the LHC

par Jean-Philippe Lansberg (IJCLab - Université Paris-Saclay - CNRS (FR))

vendredi 6 juin 2025, 14:30 → 16:30 Europe/Paris

Amphi Recherche

At ultra-relativistic velocities, such as those reached at the LHC, the (charged) beam particles can sometimes interact only via a single- or double-photon exchange. We refer to this phenomenon as a Ultra-Peripheral Collision (UPC). Effectively, this means that the LHC, with its proton and lead beams, can be used as a photon-hadron and photon-photon collider. I will review the recent progress in the field where the focus has so far been on exclusive reactions where the beam particles remain (quasi) intact and where only a well-defined system (single meson, photon pair, ...) is observed. Then, I will discuss our proposal to study inclusive photon-hadron UPCs where the "target" hadron is broken by the emitted photon. I will explain how it can help us to understand quarkonium production and how efficient the Jacquet–Blondel method to reconstruct the photon-nucleon centre-of-mass energy and the fractional energy of the quarkonium with respect to the photon is.