First measurement of the γγ → τ + τ − process and τ lepton electromagnetic moments at LHC

Inspired by recent theoretical calculations [1, 2], we propose to measure γ γ → τ+τ− using ultraperipheral heavy ion collisions at the LHC in order to probe the modified magnetic δaτ and electric dipole moments δdτ of the τ lepton. More specifically, the anomalous magnetic moment of the τ lepton, aτ = (gτ − 2)/2, lacks of a precise measurement since LEP even though it could be sensitive to physics beyond the standard model. The ATLAS and CMS experiments can rely on a suite of lepton (electron or muon) plus track(s) final states, taking full advantage of the clean photon fusion γ γ → τ+τ− events to reconstruct both leptonic and hadronic τ lepton decays. With 5–10% systematic uncertainty, the current lead-lead data set should already provide improved constraints, surpassing the 15 year old lepton collider precision by a significant factor while paving the way to improved determination at LHC Runs 3 and 4 [3]. ∗Electronic address: gkrintir@ku.edu Electronic address: mjmurray@ku.edu Electronic address: muhammad.muhammad.alibordi@cern.ch Electronic address: Yuta.Takahashi@cern.ch Electronic address: Stefanos.Leontsinis@cern.ch ∗∗Electronic address: ben.kilminster@physik.uzh.ch