Measurement of high-mass dimuon pairs from ultraperipheral lead-lead collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ATLAS detector at the LHC

Exclusive dimuon pairs with invariant mass $M_{\mu\mu} > 10$ GeV have been measured in ultra-peripheral lead-lead collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, using an integrated luminosity of 515 $\mu \mathrm{b}^{-1}$ taken with the ATLAS detector at the LHC in 2015. These very low-multiplicity interactions were recorded using an experimental trigger requiring a muon, low total transverse energy recorded in the calorimeter system, gaps at forward angles, and a reconstructed track. Events are selected to have no-other final state particles than a pair of opposite-sign dimuons. The cross section for dimuon pairs in Pb+Pb collisions is presented as a function of pair mass ($M_{\mu\mu}$) and pair rapidity ($Y_{\mu\mu}$) and is well-described by calculations of $\mathrm{Pb+Pb} \rightarrow \mathrm{{Pb}^{(*)}+{Pb}^{(*)}}+\mu^{+} + \mu^{-}$ using STARLIGHT 1.1 calculations. These data will improve the understanding of the strong electromagnetic fields surrounding the nucleus, which enable future UPC measurements utilizing these high energy probes.