Future experimental improvement for the search of lepton-number-violating processes in the eμ sector

Abstract

The conservation of lepton flavor and total lepton number are no longer guaranteed in the Standard Model after the discovery of neutrino oscillations. The μ−+N(A,Z)→e++N(A,Z−2) conversion in a muonic atom is one of the most promising channels to investigate the lepton number violation processes, and measurement of the μ−−e+ conversion is planned in future μ−−e− conversion experiments with a muonic atom in a muon-stopping target. This article discusses experimental strategies to maximize the sensitivity of the μ−−e+ conversion experiment by introducing the new requirement of the mass relation of M(A,Z−2)<M(A,Z−1), where M(A,Z) is the mass of the muon-stopping target nucleus, to eliminate the backgrounds from radiative muon capture. The sensitivity of the μ−−e+ conversion is expected to be improved by 4 orders of magnitude in forthcoming experiments using a proper target nucleus that satisfies the mass relation. The most promising isotopes found are 40Ca and 32S. © 2017 American Physical Society