Coherent photo- and electroproduction of charmonia on nuclear targets revisited: Green function formalism

TL;DR

This paper introduces a rigorous Green function formalism to study coherent charmonia production in nuclear collisions, incorporating formation effects, quantum coherence, and gluon shadowing, with results aligning well with existing data and predictions for future experiments.

Contribution

It presents the first application of a Green function formalism to coherently describe charmonia production, including formation effects and shadowing corrections, advancing theoretical understanding.

Findings

Model calculations agree with RHIC and LHC data.

Gluon shadowing dominates at mid rapidities.

Predictions made for future electron-ion collider data.

Abstract

We study for the first time the production of charmonia in nuclear ultra-peripheral and electron-ion collisions based on a rigorous Green function formalism. Such formalism allows to incorporate properly formation effects (color transparency), as well as the quantum coherence inherent in higher twist shadowing corrections related to the $|Q \bar{Q}\rangle$ Fock component of the photon. The leading twist gluon shadowing associated with multi-gluon photon fluctuations is also included within the same formalism. The later effect represents the dominant source of shadowing at mid rapidities in the LHC kinematic region, while the reduced effect of quark shadowing leads to a significant modification of differential cross sections $d\sigma/dy$ at forward and/or backwards rapidities. Model calculations for $d\sigma/dy$ are in a good agreement with available UPC data on coherent charmonium production at RHIC and the LHC. In addition, we also perform predictions for nuclear effects in the electroproduction of charmonia, which can be verified by new data from electron-ion colliders.