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LHC as an Axion-Photon Collider

Sergio Barbosa*, Matheus Coelho†, and Sylvain Fichet‡

Gustavo Gil da Silveira§

Magno Machado∥

  • CERN, PH Department, 1211 Geneva, Switzerland and Experimental Group of the CMS Collaboration (GECMS), Caixa Postal 15051, Porto Alegre, RS CEP 91501-970, Brazil

  • High Energy Physics Phenomenology Group, GFPAE IF-UFRGS, Caixa Postal 15051, Porto Alegre, RS CEP 91501-970, Brazil

  • *Contact author: sergio.barbosa@aluno.ufabc.edu.br
  • †Contact author: matheus.pereira.coelho@cern.ch
  • ‡Contact author: sylvain.fichet@gmail.com
  • §Contact author: gustavo.silveira@cern.ch
  • ∥Contact author: magno.machado@ufrgs.br
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Phys. Rev. Lett. 135, 181801 – Published 30 October, 2025

DOI: https://doi.org/10.1103/t1rl-4926

Abstract

Assuming the existence of an axionlike particle (ALP), beams of relativistic particles emit fluxes of quasireal ALPs, analogous to the photon fluxes described by Weizsäcker-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 (pA) ultraperipheral collisions. Using our implementation of ALP fluxes in simulation tools, we show that ALP-photon collisions in pPb efficiently probe ALP couplings to third generation fermions. LHC data with realistic pPb 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 pPb dataset collected at CMS, ATLAS, and LHCb should be explored for evidence of such collisions.

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synopsis

A New Kind of Collision at the LHC

Published 30 October, 2025

Researchers have proposed that exotic particles emitted by the Large Hadron Collider’s relativistic beams might reveal themselves in collisions of their own.

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Outline

Information

Phys. Rev. Lett. 135, 181801– Published 30 October, 2025
  • Received 9 July 2025
  • Accepted 10 September 2025
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