EPJ Web of Conferences 282, 01009 (2023)
https://doi.org/10.1051/epjconf/202328201009

Observation of the γγ → ττ process in Pb+Pb collisions and constraints on the τ-lepton anomalous magnetic moment with the ATLAS detector at LHC

Dipartimento di Fisica "E.Fermi" dell’Università and INFN Pisa

Published online: 3 April 2023

Abstract

This paper reports the observation of τ-lepton pair production in ultraperipheral lead-lead collisions, Pb(γ)Pb(γ) → ττ and constraints on the τ-lepton anomalous magnetic moment, a_τ, measured by the ATLAS experiment. The dataset corresponds to an integrated luminosity of 1.44 nb⁻¹ of LHC Pb+Pb collisions at $\sqrt{S_{NN}}=5.02\hspace{0.17em}\text{TeV}$. Selected events contain one muon from a τ-lepton decay, an electron or charged-particle track(s) from the other τ-lepton decay, little additional central-detector activity, and no forward neutrons. The γγ → ττ process is observed in Pb+Pb collisions with a signal strength of µ_ττ= 1.03${}_{-0.05}^{+0.06}$. To measure a_τ, a template fit to the muon transverse-momentum distribution from τ-lepton candidates is performed, using a dimuon (γγ → µµ) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for a_τ is (−0.057, 0.024).