Search for the electromagnetic moments of the τ lepton in photon–photon collisions at the LHeC and the FCC-he

Abstract

We examine the potential of the process ep → eγ * γ * p → eττ p at the Large Hadron Electron Collider (LHeC) and the Future Circular Hadron Electron Collider (FCC-he) to examine nonstandard ττ γ coupling in a model independent way by means of the effective Lagrangian approach.We perform pure leptonic and semileptonic decays for τ − τ + production in the final state. Furthermore, we use L = 10, 50, 100, 300, 500, 1000 fb −1 with at √ s = 1.30, 1.98, 7.07, 10 TeV and we consider systematic uncertainties of δ sys = 0, 5, 10%. The best sensitivity bounds obtained from the process ep → eγ * γ * p → eττ p on the anomalous couplings are −0.0025 <ã τ < 0.0009 and |d τ | < 8.85 × 10 −18 e cm, respectively. Therefore, our results show that the process ep → eγ * γ * p → eττ p at the LHeC and FCC-he are a very good prospect for probing the anomalous magnetic and electric dipole moments of the τ lepton at γ * γ * mode of the future ep collider.

Sensitivity physics expected to the measurement of the quartic WWγγ couplings at the LHeC and the FCC-he

“…In addition, the cross sections of the process ee → eγ * γ * e → eeττ at the CLIC for values of Q max = (1.41-8) GeV are obtained in reference [80]. The potential of the process ep → eγ * γ * p → eτ − τ + p at the LHeC and the FCC-he to examine non-standard τ − τ + γ coupling in a model independent way by means of the effective Lagrangian approach is investigated in reference [81]. In that study, Q max = 100 GeV is assumed and in our case, we consider the maximum photon virtuality Q max = 100 GeV, where this value is the default value in MadGraph5_aMC@NLO.…”

Anomalous electromagnetic moments of $τ$ lepton in $γγ\to τ^+ τ^-$ reaction in Pb+Pb collisions at the LHC

“…There are many existing proposals how to improve the experimental sensitivity on a τ and d τ using lepton beams and future datasets of Belle-II [24][25][26], CLIC [27,28], and LHeC [28,29]. The LHC feasibility studies focus on the usage of proton-proton collisions [28,[30][31][32][33][34] and more recently also on heavy-ion UPC [35].…”