Speaker
Description
We revisit inclusive $J/\psi$ and $\Upsilon$ photoproduction at lepton-hadron colliders, namely in the limit when the exchange photon is quasi real. Our computation includes the leading-$v$ next-to-leading order (NLO) $\alpha_s$ corrections. Similarly to the case of NLO charmonium-hadroproduction processes, the resulting cross sections obtained in the $\overline{\text{MS}}$ factorisation scheme are sometimes found to be negative. We show that the scale fixing criteria which we derived in a previous study of $\eta_c$ production successfully solves this problem. In turn, we argue that both $J/\psi$ and $\Upsilon$ photoproduction can be used to set stringent constraints on the poorly constrained gluon densities at scales as low as a couple of GeV.