New Process for Charged Lepton Flavor Violation Searches: μ-e- → e-e- in a Muonic Atom

We propose a new process of mu(-)e(-) -> e(-)e(-) in a muonic atom for a quest of charged lepton flavor violation. The Coulomb attraction from the nucleus in a heavy muonic atom leads to significant enhancement in its rate, compared to mu(-)e(-) -> e(-)e(-). The upper limit of the branching ratio is estimated to be of the orders of O(10(-17)-10(-18)) for the photonic and the four-fermion interactions from the present experimental constraints. The search for this process could serve complementarily with the other relevant processes to shed light upon the nature of charged lepton flavor violation.