Quarkonia are a perfect tool for testing QCD and hadronisation. Plenty
of data from hadron-hadron and lepton-hadron colliders are available,
but there is still a debate on the quarkonium production mechanism.
Among different models for quarkonium production, the Colour Singlet
Model (CSM), the Colour Evaporation Model (CEM), and the
Non-Relativistic QCD (NRQCD) framework are the most used ones.
Within the NRQCD, a double expansion in $\alpha_s$ and in $v$, the heavy
quark-antiquark pair relative velocity, is done, and the hadronisation
of partons into a quarkonium is described in terms of Long-Distance
Matrix Elements (LDMEs). Current LDME fits cannot describe at the same
time the quarkonium production in different processes (as
hadroproduction or photoproduction). To this extent, re-examining some
of these processes in the CSM (that represents the leading-$v$
contribution of NRQCD) may be helpful for easing some of the issues
currently faced in quarkonium physics.
In this talk, we present some recent studies on inclusive quarkonium
photoproduction at lepton-hadron colliders at NLO in QCD in the CSM.
First, we focus on transverse momentum differential cross sections for
J/$\psi$ production. We show how, by properly accounting for some
contributions as the feed-downs and the associated J/$\psi$+charm
production, the photoproduction data from HERA can be described within
the CSM. Then, we analyse the issue of negative integrated cross
sections for inclusive quarkonium photoproduction at NLO in QCD. A
solution to this problem is proposed, and predictions for future
colliders such as the EIC and LHeC are given.
Wednesday, 28th June 2023, 14:30 — Sala Wataghin