Nuclear aspects of neutral current non-standard $\nu$-nucleus reactions and the role of the exotic ${\mu }^{-}\to e^{-}$ transitions experimental limits

Abstract

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 ${\nu }_{\ell }$ and ${\tilde{\nu }}_{\ell }$, $\ell =e,\mu ,\tau$ and (ii) in charged lepton flavour violating (cLFV) processes involving the charged leptons ${\ell }^{-}$ or ${\ell }^{+}$. As concrete nuclear systems we have chosen the stopping targets of ${\mu }^{-}\to e^{-}$ conversion experiments, i.e. the ${}^{48}\mathrm{Ti}$ nucleus of the PRIME/PRISM experiment at J-PARC and the ${}^{27}\mathrm{Al}$ 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 ${\mu }^{-}\to e^{-}$ experiments, to put stringent constraints on the parameters of NSI Lagrangians.

Comments: 8 pages, 4 figures, 3 Tables, Physics Letters B accepted