Search for resonances in light-by-light scattering using the forward proton detectors at the LHC-ATLAS

A search for light-by-light scattering mediated by an axion-like particle at the LHC is presented, using the central ATLAS detector to detect pairs of outgoing photons and the ATLAS Forward Proton spectrometer to detect scattered intact protons which produce the photons. Proton--proton collision data recorded in 2017 at a centre-of-mass energy of $\sqrt{s} = 13$ TeV were analysed, corresponding to an integrated luminosity of 14.6 fb$^{-1}$. A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range $150$--1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant.