Photon-initiated enhancements in the pair production of highly charged coloured particles

TL;DR

This paper investigates how mixed QCD-QED contributions from gluon-photon initial states significantly enhance the pair production of highly charged coloured particles like leptoquarks at the LHC, affecting experimental bounds.

Contribution

It demonstrates that mixed QCD-QED effects can increase production rates of highly charged states by up to 33%, impacting mass exclusion limits and requiring more precise modeling.

Findings

Mixed QCD-QED contributions can enhance pair-production rates by up to 33%.

The effects influence jet multiplicities and angular distributions in collider events.

Recasting ATLAS data shows these QED effects strengthen mass exclusion limits.

Abstract

Strong interaction is typically assumed to dominate the pair production of heavy coloured resonances at the LHC. However, mixed QCD-QED contributions from gluon-photon ($g\gamma$) initial states become critical for highly charged states. This contribution scales with the square of their electric charges and maximises for particles in the fundamental colour representation. We study this effect for leptoquarks, which are colour-triplet bosons. We demonstrate that tree-level mixed QCD-QED contributions enhance their pair-production rates by up to $\sim 33\%$ for a charge-$5/3$ state, rivalling the size of next-to-leading-order QCD corrections. The asymmetric colour flow of $g\gamma$ fusion affects the radiation pattern, altering jet multiplicities and angular distributions. By recasting the latest ATLAS $\mu\mu jj$ search data, we find that these often-overlooked QED effects systematically strengthen mass exclusion limits, establishing a necessary precision standard for bounding highly charged coloured states.