Elastic and inelastic $J/\psi$ photoproduction in $p$-$p$ collisions at LHC energies: the feature of Weizs\"{a}cker-Williams approximation

TL;DR

This paper investigates elastic and inelastic $J/$ photoproduction in proton-proton collisions at LHC energies, comparing exact calculations with the Weizsker-Williams approximation to improve accuracy and understand contributions from different processes.

Contribution

The study provides a comprehensive analysis of $J/$ photoproduction, highlighting the limitations of WWA and emphasizing the importance of exact treatment for accurate results.

Findings

Incoherent-photon emission significantly contributes to elastic photoproduction.

Photon and fragmentation processes enhance $J/$ production at LHC energies.

WWA is only valid in limited kinematic regions; exact methods are necessary.

Abstract

The $J/\psi$ production originating from elastic and inelastic photoproduction processes in p-p collisions at LHC energies is investigated, where the fragmentation processes are involved. An exact treatment is performed, which adopts the Martin-Ryskin method to weight the contribution from different channels, and can return to Weizs\"{a}cker-Williams approximation (WWA) when $Q^{2}\rightarrow0$. The relevant kinematical relations are also achieved. We present a comprehensive analysis for the feature of WWA by comparing with the exact treatment. The results are expressed in $Q^{2}$, $y$, $z$, $p_{T}$, and $y_{r}$ (rapidity) distributions, and the total cross sections are also estimated. The numerical results indicate that, the incoherent-photon emission can provide the meaningful contribution to elastic photoproduction, and starts to play a very important role in the inelastic processes. The photoproduction and fragmentation processes can improve the contribution of $J/\psi$ production in $p$-$p$ collisions at LHC energies. Moreover, the WWA is only effective in very restricted domains, and the exact treatment is needed to deal accurately with the $J/\psi$ photoproduction, which can naturally avoid double counting and WWA errors.