Diffractive dijets in 𝑒 𝑝 𝑒′ 𝑗𝑒𝑡 𝑗𝑒𝑡 𝑝 reaction using GTMDs

Exclusive (diffractive) dijet production in ep scattering provides direct access to transverse-momentum dependent gluon dynamics at small~x. We summarize a momentum-space dipole/GTMD calculation of ep e\, p\, jj in which the diffractive amplitude is expressed through off-forward unintegrated gluon distributions (gluon GTMDs). Several GTMD models from the literature are confronted with H1 and ZEUS measurements under the corresponding experimental cuts. With the exception of a GTMD tuned to a subset of H1 observables, the exclusive q q channel typically undershoots the measured cross sections; ZEUS data impose the strongest constraints. We also show that sizeable azimuthal modulations between the dijet momentum sum and difference can be generated purely by jet pT cuts, potentially mimicking signals of elliptic gluon distributions.