Electron-to-Tau Lepton Flavor Violation at the Electron-Ion Collider

TL;DR

This paper evaluates the potential of the proposed electron-ion collider to detect electron-to-tau lepton flavor violation via leptoquark interactions, potentially surpassing current experimental limits and exploring new parameter space.

Contribution

It provides a detailed analysis of EIC sensitivity to $e\rightarrow\tau$ conversion mediated by leptoquarks, including updated limits and theoretical model implications.

Findings

EIC could probe previously unexplored leptoquark parameter space.

EIC sensitivity may surpass HERA and rare decay limits by an order of magnitude.

Observable $e\rightarrow\tau$ conversion consistent with LFV constraints in GUT models.

Abstract

We analyze the potential sensitivity of a search for $e\rightarrow\tau$ conversion at a proposed electron-ion collider (EIC) facility. To that end, we calculate the cross sections for $e\rightarrow\tau$ events in a leptoquark framework assuming that the leptoquark masses are on the order of several hundred GeV or more. Given present limits on leptoquarks from direct searches at HERA and rare decay processes, an EIC sensitive to 0.1 fb $e\rightarrow\tau$ cross sections could probe previously unexplored regions of parameter space for these lepton flavor violating events (assuming 90 GeV center-of-mass energy and 10 fb$^{-1}$ integrated luminosity). Depending on the species of leptoquark and flavor structure of the couplings, an EIC search could surpass the HERA and rare process sensitivity to $e\rightarrow\tau$ conversion amplitudes by as much as an order of magnitude or more. We also derive updated limits on quark flavor-diagonal LFV leptoquark interactions using the most recent BaBar $\tau\rightarrow e\gamma$ search. We find that limits from an EIC $e\rightarrow\tau$ search could be competitive with the most recent $\tau\rightarrow e\gamma$ limit for a subset of the quark flavor-diagonal leptoquark couplings. Using an SU(5) GUT model in which leptoquark couplings are constrained by the neutrino masses and mixing, we illustrate how observable leptoquark-induced $e\rightarrow\tau$ conversion can be consistent with stringent LFV limits imposed by $\mu\rightarrow e\gamma$ and $\mu\rightarrow e$ conversion searches.