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The transverse momentum transfer can be measured in exclusive processes. As this momentum transfer is Fourier conjugate to the impact parameter, exclusive processes in Ultra Peripheral Collisions (UPC) at the LHC and at the future EIC will provide access to the spatial distribution of nuclear matter in light and heavy nuclei at high energies.
In this talk we show how non-linear saturation effects change the spatial density profile of a heavy nucleus, and that such modifications are necessary in order to obtain a good description of the exclusive J/psi production as measured by the ALICE and LHCb collaborations in Pb+Pb UPCs at the LHC. We also demonstrate that the LHC data shows preference for a larger nuclear strong-interaction radii compared to the typical charge radius. We demonstrate the role of a finite photon transverse momentum and the interference between the cases for which the role of photon emitter and target are switched between the nuclei. We show that these effects are comparable to the experimental precision for p_T differential cross sections and as such need to be included when comparing to LHC data.
We also demonstrate how exclusive J/psi production off uranium targets is sensitive to the geometric deformations at high energy. Such deformations have been extracted from low-energy measurements, but we demonstrate the potential of future EIC measurements to extract the quadrupole, octupole, and hexadecapole deformations. We also study J/psi production in e+Ne and e+O collisions and show how the deformed structure of the neon increases the incoherent cross section significantly in the relatively low momentum transfer region, which can be used to probe how such deformations change in the the high-energy and high-density domain.
References:
H. Mäntysaari, F. Salazar, B. Schenke, Phys.Rev.D 106 (2022) 7, 074019, arXiv:2207.03712
H. Mäntysaari, B. Schenke, C. Shen, W. Zhao, arXiv:2303.04866 [nucl-th]