Exclusive dielectron production in ultraperipheral Pb+Pb collisions at √s_NN = 5.02 TeV with ATLAS

Exclusive production of dielectron pairs, γγ→e⁺e⁻, is studied using L_int=1.72nb⁻¹ of data from ultraperipheral collisions of lead nuclei at √s_NN = 5.02 TeV recorded by the ATLAS detector at the LHC. The process of interest proceeds via photon-photon interaction in the strong electromagnetic fields of relativistic lead nuclei. Dielectron production is measured in the fiducial region defined by following requirements: electron transverse momentum, p^e_T>2.5 GeV, absolute electron pseudorapidity, |η^e|<2.5, invariant mass of the dielectron system, m_ee>5 GeV, and transverse momentum of the dielecton pair, p^ee_T<2 GeV. Differential cross-sections are measured as a function of m_ee, average p^e_T, absolute rapidity of the dielectron system, |y_ee|, and scattering angle in the dielectron rest frame, |cosθ^∗| in the inclusive sample, and also under the requirement of no activity in the forward direction. The total integrated fiducial cross-section is measured to be 215±1(stat.)⁺²³₋₂₀(syst.)±4(lumi.)μb. Within experimental uncertainties the measured integrated cross-section is in good agreement with the QED predictions from the Monte Carlo programs Starlight and SuperChic, confirming the broad features of the initial photon fluxes. The differential cross-sections show systematic differences with these predictions which are more pronounced at high |y_ee| and |cosθ^∗| values.