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Gluon density and its distributions inside nuclei and the parton modificationof bounded nucleons inside a nucleus, are some of the main standing problems innuclear and particle physics. In recent years, ultra-peripheral collisions(UPC) of heavy ions have provided a new way of probing the gluon density, whichis based on coherent diffractive vector-meson productions, e.g., $J/\psi$meson. For heavy ions, e.g., Pb, the gluon density is found to be significantlysuppressed through the UPC $J/\psi$ measurement, suggesting a strong gluonshadowing effect in heavy nuclei. In this analysis, we aim to look at a uniqueset of data taken by the STAR experiment, where $J/\psi$ mesons arephotoproduced off the deuteron target with no other particle produced, exceptfor the deuteron or its breakup products. The Zero Degree Calorimeter responsewith respect to the deuteron dissociation by detecting a beam-rapidity neutronis also investigated and provides additional information about the underlyingphysics process. The cross section of $J/\psi$ photoproduction in thephoton-deuteron system is measured at the photon-nucleon center-of-mass energy$W\sim25~\rm{GeV}$, as well as the momentum transfer $t$ dependence crosssection, $d\sigma/dt$. Data suggests a wider gluon density distribution thanthe Hulthen charge density distribution in deuteron.

Exclusive $J/\psi$ photoproduction off deuteron in d+Au ultra-peripheral collisions at STAR