Nuclear aspects of neutral current non-standard ν -nucleus reactions and the role of the exotic μ−→e−μ−→e− transitions experimental limits

The nuclear aspects of flavour changing neutral current (FCNC) processes, predicted by various new-physics models to occur in the presence of nuclei, are examined by computing the relevant nuclear matrix elements within the context of the quasi-particle RPA using realistic strong two-body forces. One of our aims is to explore the role of the non-standard interactions (NSI) in the leptonic sector and specifically: (i) in lepton flavour violating (LFV) processes involving the neutral particles νℓνℓ and ν˜ℓ, ℓ=e,μ,τℓ=e,μ,τ and (ii) in charged lepton flavour violating (cLFV) processes involving the charged leptons ℓ−ℓ− or ℓ+ℓ+. As concrete nuclear systems we have chosen the stopping targets of μ−→e−μ−→e− conversion experiments, i.e. the 48Ti nucleus of the PRIME/PRISM experiment at J-PARC and the 27Al of the COMET at J-PARC as well as of the Mu2e at Fermilab. These experiments have been designed to reduce the single event sensitivity down to 10−16–10−18 in searching for charged lepton mixing events. Our goal is, by taking advantage of our detailed nuclear structure calculations and using the present limits or the sensitivity of the aforementioned exotic μ−→e−μ−→e− experiments, to put stringent constraints on the parameters of NSI Lagrangians.