Diffractive open charm photoproduction in ultraperipheral lead-lead and proton-lead collisions at the LHC

Abstract

We calculate diffractive $D^{0}$ photoproduction in ultraperipheral lead--lead (Pb--Pb) collisions at the Large Hadron Collider (LHC) within the recently developed G$γ$A--FONLL framework, where photon--lead diffraction is modeled using nuclear diffractive parton distributions obtained in the leading twist shadowing approach and the photon fluxes include corrections for independent electromagnetic dissociation accompanying the hard photoproduction process. We then use the predicted diffractive cross section to quantify the coherent diffractive contribution rejected by the $Xn0n$ neutron-tagged event selection adopted in the first measurement of $D^0$ photoproduction in Pb-Pb collisions at the LHC, which requires neutron emission from only one of the two lead nuclei. In this work, we also extend the G$γ$A--FONLL framework to proton--lead ($p$--Pb) UPCs and present predictions for inclusive and diffractive $D^{0}$ photoproduction at the LHC. In this case, the dominant configuration is photon emission from the lead ion followed by photon--proton scattering, and the diffractive contribution is evaluated using proton diffractive parton distributions constrained by HERA data.