Search for the electromagnetic moments of the $\tau$ lepton in photon-photon collisions at the LHeC and the FCC-he

Abstract

We examine the potential of the process $ep \rightarrow e\gamma^{*} \gamma^{*} p\rightarrow e\tau \bar{\tau}p$ at the Large Hadron Electron Collider (LHeC) and the Future Circular Hadron Electron Collider (FCC-he) to examine non-standard $\tau\bar{\tau}\gamma$ coupling in a model independent way by means of the effective Lagrangian approach. We perform pure leptonic and semileptonic decays for $\tau^{-}\tau^{+}$ production in the final state. Furthermore, we use $L = 10, 50, 100, 300, 500, 1000$ fb$^{-1}$ with at $\sqrt{s}=1.30, 1.98, 7.07, 10$ TeV and we consider systematic uncertainties of $\delta_{sys}=0,5,10 \%$. The best sensitivity bounds obtained from the process $ep \rightarrow e\gamma^{*} \gamma^{*} p\rightarrow e\tau \bar{\tau}p$ on the anomalous couplings are $-0.0025<\tilde{a}_{\tau}<0.0009$ and $|\tilde{{d}_{\tau}}|<8.85 \times 10^{-18}\, e\,cm$, respectively. Therefore, our results show that the process $ep \rightarrow e\gamma^{*} \gamma^{*} p\rightarrow e\tau \bar{\tau}p$ at the LHeC and FCC-he are a very good prospect for probing the anomalous magnetic and electric dipole moments of the $\tau$ lepton at $\gamma^{*} \gamma^{*}$ mode of the future $ep$ collider.