We extend a previous GTMD model to improve the description of the HERA data
on diffractive dijet production, and include exclusive coherent diffractive
J/ψ production data. We find that within our gluon GTMD model context and
assumptions, there is considerable tension between the data for these two types
of processes concerning the t dependence. Photo- and electroproduction data
for protons and nuclei from EIC and UPC data from LHC and RHIC can help to
establish whether a common GTMD description is possible, as one would expect,
and to facilitate studies of such data we provide predictions for the various
experiments. We point out explicitly in which sense this goes beyond the
description in terms of GPDs.Comment: 15 pages, 19 figures; new references added and some modifications of
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