Improved analyses forμ−e−→e−e−

Abstract

The charged lepton flavor violating (CLFV) processes of µ − e − → e − e − decay by four Fermi contact interactions in a muonic atom for various atoms are investigated. The wave functions of bound and scattering state leptons are properly treated by solving Dirac equations with Coulomb interaction of the finite nuclear charge distributions. This new effect contributes significantly in particular for heavier atoms, where the obtained decay rate is about one order of magnitude larger than the previous estimation for 208 Pb. We find that, as the atomic number Z increases, the µ − e − → e − e − decay rates increase more rapidly than the result of the previous work of Z 3 , suggesting this decay as one of the promising processes to search for CLFV interaction.

LFV golden channels and effective-field theories

“…The present analysis is far from being exhaustive; indeed, intriguing new ideas to explore the effective parameter space appeared recently in the literature [28,29,30,31,32], and their RGEimproved analysis should be included in the present treatment.…”

Distinguishing muon LFV effective couplings using $\mu+e^-\rightarrow e^-+e^-$

“…[5]. In our recent work [6,7], we performed careful calculation for the rate of µ − e − → e − e − in a muonic atom. In this paper, we focus on the µ − e − → e − e − search with a muon polarized in a muonic atom to extract the chiral property of the CLFV interaction,…”

Selecting μ → e conversion targets to distinguish lepton flavour-changing operators

“…The isotope abundances are from [30]. The parameter B Z is defined in eqn (8). The estimate for S Au p is based on the Odd Group Model of [24], assuming J=1/2.…”

“…We anticipate that µ → e conversion could constrain 10 to 14 combinations of coefficients; if µ → eγ and µ → eēe constrain eight more, that leaves 60 to 64 "flat directions" in the basis of QED×QCD-invariant operators which describe µ → e flavour change below § Another interesting observable at these experiments is the µ − e − → e − e − in a muonic atom. This process could have not only photonic dipole but also contact interactions, and the atomic number dependence of its reaction rate makes possible to discriminate the type of relevant CLFV interactions [7,8,9]. * * Since the current MEG bound on the dipole coefficients constrains them to be below the sensitivity of the current µ → e conversion bounds, the dipole overlap integral was set to zero in obtaining this Figure.…”