Speaker
Description
Using the Colour Glass Condensate effective theory, we study the diffractive
production of a massive quark-antiquark pair accompanied by a gluon in coherent photon-
nucleus collisions at high energy. This partonic configuration provides the leading twist
contribution to the cross section in the correlation limit where two of the partons are hard
and nearly back to back in the transverse plane, while the third one is semi-hard, with a
transverse momentum of the order of the nuclear saturation momentum. We consider two
scenarios: (i) a hard quark-antiquark pair together with a semi-hard gluon; in this case we
demonstrate transverse momentum dependent (TMD) factorization with a mass-dependent
“hard” factor and the standard expression for the gluon diffractive TMD, and (ii) a hard
antiquark-gluon pair and a semi-hard quark; in this case we find TMD factorization with
a mass-independent “hard” factor and a mass-dependent quark diffractive TMD, which
represents a new result. We show that increasing the quark mass reduces (or even washes
out) the effects of gluon saturation on the quark diffractive TMD. In particular, it leads to
the suppression of the Cronin peak that we observe in the massless limit. Our results are
the basis for future phenomenological studies of quarkonium and open charm production
in the saturation regime in ultraperipheral collisions at the Large Hadron Collider, and in
deep inelastic scattering at the Electron-Ion Collider