Exclusive heavy quark-pair production in ultraperipheral collisions

In this article, we study the fully differential observables of exclusive production of heavy (charm and bottom) quark pairs in high-energy ultraperipheral $pA$ and $AA$ collisions. In these processes, the nucleus $A$ serves as an efficient source of the photon flux, while the QCD interaction of the produced heavy-quark pair with the target ($p$ or $A$) proceeds via an exchange of gluons in a color singlet state, described by the gluon Wigner distribution. The corresponding predictions for differential cross sections were obtained by using the dipole $S$-matrix in the McLerran--Venugopalan saturation model with impact parameter dependence for the nucleus target, and its recent generalization, for the proton target. Prospects of experimental constraints on the gluon Wigner distribution in this class of reactions are discussed.