On the model discriminating power of mu -> e conversion in nuclei

TL;DR

This paper evaluates how well muon-to-electron conversion experiments can distinguish different theoretical models of lepton flavor violation, emphasizing the importance of reducing uncertainties and precise ratio measurements.

Contribution

It demonstrates that reducing hadronic uncertainties enhances model discrimination and identifies the experimental precision needed for effective differentiation.

Findings

Theoretical uncertainties can be minimized with lattice QCD inputs.

Discrimination requires 5% ratio measurement for light nuclei.

Discrimination requires 20% ratio measurement for mixed nuclei.

Abstract

We assess the model discriminating power of a combined phenomenological analysis of mu -> e gamma and mu -> e conversion on different target nuclei, including the current hadronic uncertainties. We find that the theoretical uncertainties can be largely reduced by using input from lattice QCD and do not constitute a limiting factor in discriminating models where one or at most two underlying operators (dipole, scalar, vector) provide the dominant source of lepton flavor violation. Our results show that a realistic discrimination among underlying mechanisms requires a measurement of the ratio of conversion rates at the 5% level (two light nuclei) or at the 20% level (one light and one heavy nucleus). We have illustrated these main conclusions also in the context of a supersymmetric model.