Determination of coupling patterns by parallel searches for μ- → e+ and μ- → e- in muonic atoms

We investigate a possibility that the mu(-) -> e(+) conversion is discovered prior to the mu(-) -> e(+) conversion, and its implications to the new physics search. We focus on the specific model including the mixing of the SU (2)(L) doublet-and singlet-type scalar leptoquarks, which induces not only the lepton flavor violation but also the lepton number violation. Such a structure is motivated by R-parity violating (RPV) supersymmetric models, where a sbottom mediates the conversion processes. We formulate the mu(-) -> e(+) rate in analogy with the muon capture in a muonic atom, and numerically evaluate it using several target nuclei. The lepton flavor universality test of pion decay directly limits the mu(-) -> e(+) rate, and the maximally allowed mu(-) -> e(+) branching ratio is similar to 10(-18) under the various bounds on RPV parameters. We show that either mu(-) -> e(-) or mu(-) -> e(+) signals can be discovered in near future experiments. This indicates that parallel searches for these conversions will give us significant information on the pattern of coupling constants. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).

Automated summary

We investigate the possibility of discovering the mu(-) -> e(+) conversion before the mu(-) -> e(+) conversion and its implications for new physics search. We focus on a specific model involving the mixing of scalar leptoquarks of SU(2)(L) doublet and singlet types, which not only induces lepton flavor violation but also lepton number violation. This structure is motivated by R-parity violating (RPV) supersymmetric models, where a sbottom mediates the conversion processes. Numerical evaluations show that either mu(-) -> e(-) or mu(-) -> e(+) signals can be discovered in near future experiments, providing significant information on the pattern of coupling constants.