Abstract
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.
Highlights
In QCD, the hadron structure is encoded in the so-called Wigner distributions [1,2,3]
While the Wigner distribution is in impact-parameter b⃗ ⊥ representation, their Fourier transform as b⃗ ⊥ → Δ⃗ ⊥ is known as the generalized transverse momentum distribution (GTMD) [4,5,6,7] in momentum representation
These distributions are sensitive to the angular correlation between b⃗ ⊥ and k⃗ ⊥ whose magnitude is determined by the elliptic Wigner distribution [8,9,10]
Summary
In QCD, the hadron structure is encoded in the so-called Wigner distributions [1,2,3]. As a price to pay for such an improvement, for heavy quarks the convolution integral in the diffractive amplitude is no longer analytically invertible, so for we can only make predictions for the corresponding observables in the framework of a given model for the gluon Wigner distribution LIGHT-CONE DIPOLE APPROACH FOR EXCLUSIVE HEAVY-QUARK PAIR PHOTOPRODUCTION IN UPCs
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