The LHC as an Axion-Photon Collider

TL;DR

This paper explores the potential of the LHC to act as a collider for axion-like particles (ALPs), proposing new methods to probe ALP couplings through ALP-photon collisions in proton-ion ultraperipheral collisions.

Contribution

It introduces the concept of using the LHC as an ALP collider and demonstrates that ALP-photon collisions in $p$A ultraperipheral collisions can effectively probe ALP couplings, especially to third-generation fermions.

Findings

ALP fluxes from heavy ions are suppressed compared to protons.

ALP-photon collisions in $p$Pb can constrain ALP couplings to nucleons and top quarks.

Existing 2016 $p$Pb data can be used to search for ALP signals.

Abstract

Assuming the existence of an axion-like particle (ALP), beams of relativistic particles emit fluxes of quasi-real ALPs, analogous to the photon fluxes described by Weizs\"acker-Williams-type approximations. Consequently, ALP-ALP and ALP-photon collisions can occur at the LHC. We initiate the study of the LHC as an ALP collider, and show that ALP collisions provide competitive probes of certain ALP couplings. We show that ALP fluxes from heavy ions are suppressed relative to those from protons, unlike their photon counterpart. As a result, the most likely processes are ALP-photon collisions occurring in the proton-ion ($p$A) ultraperipheral collisions. Using our implementation of ALP fluxes in simulation tools, we show that ALP-photon collisions in $p$Pb efficiently probe ALP couplings to third generation fermions. LHC data with realistic $p$Pb luminosity can constrain the product of ALP couplings to nucleons and top quarks at the level of $O(0.01$ TeV$^{-1})$. Notably, ALP-photon collisions naturally provide the leading probe of ALP flavor-violating couplings to the top quark. We suggest that the 2016 $p$Pb dataset collected at CMS, ATLAS, and LHCb should be explored for evidence of such collisions.