Threshold effects in high-energy vortex state collisions

Collisions of particles prepared in non--plane-wave states with a non-trivial phase structure, such as vortex carrying an adjustable orbital angular momentum (OAM), open novel opportunities atomic, nuclear, and high-energy physics unavailable for traditional scattering experiments. Recently, it was argued that photoinduced processes $\gamma d \to pn$ p \Delta^+$ initiated by photon should display remarkable threshold shift sizable cross section enhancement the impact parameter $b$ target hadron respect to axis goes zero. In this work, we theoretically explore whether effect exists within quantum-field-theoretic treatment process. We do not rely on semiclassical assumption pointlike, non-spreading particle and, instead, consider toy process heavy pair production collision two light Laguerre-Gaussian compact Gaussian wave packets, paying special attention behavior section. observe smearing due non-monochromaticity but confirm near-threshold enhancement. Instead find OAM-related dip at $b\to 0$ compared packet collision.