Diffractive dijets in 𝑒 𝑝 $\rightarrow$ 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 $ep\to e\,p\,jj$ 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 $q\bar q$ 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 $p_T$ cuts, potentially mimicking signals of elliptic gluon distributions.