Muon–electron conversion in a family gauge boson model

Abstract

We study the μ–e conversion in muonic atoms via an exchange of family gauge boson (FGB) A21 in a U(3) FGB model. Within the class of FGB model, we consider three types of family-number assignments for quarks. We evaluate the μ–e conversion rate for various target nuclei, and find that next generation μ–e conversion search experiments can cover entire energy scale of the model for all of types of the quark family-number assignments. We show that the conversion rate in the model is so sensitive to up- and down-quark mixing matrices, Uu and Ud, where the CKM matrix is given by VCKM=Uu†Ud. Precise measurements of conversion rates for various target nuclei can identify not only the types of quark family-number assignments, but also each quark mixing matrix individually.