K+K− photoproduction in ultra-peripheral Pb–Pb collisions

In ultra-peripheral collisions (UPCs) of relativistic heavy ions, photoproduction occurs when a photon emitted from one nucleus interacts with the other nucleus from the opposing beam, producing particles in the final state. Measurements of KK photoproduction probe interactions and couplings between the phi (1020) and charged kaons with photons and nuclear targets. We report the exclusive KK photoproduction cross section at midrapidity in Pb–Pb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV, which is measured for the first time in UPCs.