Inclusive quarkonium photoproduction selection and the effect of pileup at the LHC

TL;DR

This paper addresses the challenge of measuring inclusive quarkonium photoproduction at the LHC by detailing a selection strategy optimized for $p$Pb ultra-peripheral collisions, where photon flux, luminosity, and low pileup balance favor measurement. It analyzes how to extend the approach to PbPb and the more challenging $pp$ environments, emphasizing centrality selection via ZDCs, forward-neutron vetoes, and rapidity-gap observables across detector acceptances. The work highlights the impact of pileup on forward-detector-based selections and rapidity-gap efficiencies, showing that the discriminating power of these criteria is reduced in high-pileup scenarios, particularly for $pp$ collisions. The findings argue that inclusive quarkonium photoproduction measurements are feasible in peripheral heavy-ion systems and stress the need for pileup-aware optimization to realize LHC measurements that can constrain production mechanisms and inform photon-induced processes in hadronic collisions.

Abstract

Measurements of inclusive quarkonium photoproduction provide strong constraints on the quarkonium production mechanism; however, this process has not yet been measured at the LHC. We summarise our previously developed selection strategy for isolating inclusive quarkonium photoproduction in pPb collisions at the LHC, which offer an optimal balance of photon flux, luminosity, and low pileup. We further examine the applicability of our selection criteria in different collision systems. While our method can be readily extended to PbPb collisions, pp collisions require additional care due to the significantly higher pileup. We discuss how pileup affects the selection criteria, highlighting that it substantially degrades forward-detector-based selections and reduces the efficiency of rapidity-gap requirements.

Figures (2)

• Figure 1: (a) exclusive diffractive photoproduction; (b) diffractive photoproduction with nuclear break up; (c) inclusive photoproduction; (d) inclusive hadroproduction. Figures are produced using FeynGame Bundgen:2025utt.
• Figure 2: Comparison between (a) $\Delta\eta_\gamma$ and (b) $\sum\Delta\eta_\gamma$ for $J/\psi$ using the singlet (dashed) and octet (solid) tunes of direct photoproduction (blue) and hadroproduction (grey) in the peripheral limit with $N_\text{coll}=1$. The lower panel shows the relative statistical (dotted) and systematic (solid) uncertainties as a function of the cut value on $\Delta \eta_\gamma$ or $\sum\Delta\eta_\gamma$. The dotted vertical line indicates the cut value that minimises the statistical uncertainty following the background subtraction.