Two-to-two processes at an electron-muon collider

TL;DR

This paper evaluates the potential of an electron-muon collider to probe new physics through two-to-two processes, comparing its sensitivity to low-energy experiments and highlighting its strengths for second and third family fermions.

Contribution

It provides a comparative analysis of collider sensitivity to effective operators versus low-energy measurements, emphasizing the collider's unique advantages for certain fermion families.

Findings

Collider sensitivity is weaker for first family fermions.

For second and third family fermions, collider sensitivity is comparable or superior.

Gamma gamma production offers the strongest sensitivity to dimension 8 operators.

Abstract

Based on a recent proposal to build an electron-muon collider, we study two-to-two production processes e^- mu^+ --> f bar-f, gamma gamma that originate from dimension 6 and 8 operators. We compare the sensitivity to those effective couplings obtained at the collider with that of low energy measurements of mu --> e gamma, mu --> e bar-e e and mu --> e conversion that have recently been reported in the literature. Whereas for the production of first family fermions the sensitivity of the collider processes is much weaker, for the second and third family fermions it is similar or stronger than that of low-energy processes. In the case of e^- mu^+ --> gamma gamma, the sensitivity to a dimension 8 contact operator turns out to be the strongest in comparison.