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arXiv · 2404.09731

Spatial resolution of dijet photoproduction in near-encounter ultraperipheral nuclear collisions

Kari J. Eskola·Vadim Guzey·Ilkka Helenius·Petja Paakkinen·Hannu Paukkunen
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Abstract

We present next-to-leading order perturbative QCD predictions for inclusive dijet photoproduction in ultra-peripheral nucleus-nucleus collisions (UPCs) within the impact-parameter dependent equivalent photon approximation. Taking into account the finite size of both the photon-emitting and the target nucleus, we show that this process is sensitive to the transverse-plane geometry of the UPC events. We show that this leads to a sizeable, 20-40% effect for large values of the $z_\gamma$ variable in the dijet photoproduction cross section in lead-lead UPCs at 5.02 TeV compared to the widely-used pointlike approximation where the nuclear radius is accounted for only as a sharp cut-off in the photon flux calculation. This resolution of the spatial degrees of freedom is a result of having high-transverse-momentum jets in the final state, which at the large-$z_\gamma$ kinematics requires a highly energetic photon in the initial state, thus biasing the collisions to small impact-parameter ''near-encounter'' configurations. We further discuss the role of the forward-neutron event-class selection in isolating the photonuclear cross section in the nucleus-nucleus collisions, and employ the needed electromagnetic breakup survival factor in our predictions.

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Kari J. Eskola, Vadim Guzey, Ilkka Helenius, Petja Paakkinen, Hannu Paukkunen. 2024-04-15. Spatial resolution of dijet photoproduction in near-encounter ultraperipheral nuclear collisions. https://arxiv.org/abs/2404.09731

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