Observation of the γγ→ττ Process in Pb+Pb Collisions and Constraints on the τ-Lepton Anomalous Magnetic Moment with the ATLAS Detector

G. Aad, T.P.A. Åkesson, E.E. Corrigan, C. Doglioni, P.A. Ekman, J. Geisen, V. Hedberg, G. Jarlskog, B. Konya, E. Lytken, K.H. Mankinen, J.U. Mjörnmark, G.A. Mullier, R. Poettgen, N.D. Simpson, E. Skorda, O. Smirnova, L. Zwalinski, ATLAS Collaboration

Research output: Contribution to journalArticlepeer-review

Abstract

This Letter reports the observation of τ-lepton-pair production in ultraperipheral lead-lead collisions Pb+Pb→Pb(γγ→ττ)Pb and constraints on the τ-lepton anomalous magnetic moment a_{τ}. The dataset corresponds to an integrated luminosity of 1.44  nb^{-1} of LHC Pb+Pb collisions at sqrt[s_{NN}]=5.02  TeV recorded by the ATLAS experiment in 2018. 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 significance exceeding 5 standard deviations and a signal strength of μ_{ττ}=1.03_{-0.05}^{+0.06} assuming the standard model value for a_{τ}. 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
Original languageEnglish
Article number151802
JournalPhysical Review Letters
Volume131
Issue number15
DOIs
Publication statusPublished - 2023

Subject classification (UKÄ)

  • Subatomic Physics

Free keywords

  • Magnetic moments
  • Anomalous magnetic moments
  • ATLAS detectors
  • ATLAS experiment
  • Integrated luminosity
  • Lead collisions
  • Lepton pairs
  • Moment formula
  • Pair production
  • Particle tracks
  • Standard deviation
  • Charged particles

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