New constraints on R-parity violation from μ–e conversion in nuclei

We derive new constraints on the products of explicitly R-parity violating couplings λ and λ′ in MSSM from searches for μ–e conversion in nuclei. We concentrate on the loop induced photonic coherent conversion mode. For the combinations |λλ| which in μ–e conversion can be probed only at loop level our constraints are in many cases more stringent than the previous ones due to the enhancement of the process by large ln(m2f/m2f̃). For the combinations of |λ′λ′| the tree-level μ–e conversion constraints are usually more restrictive than the loop ones except for two cases which involve the third generation. With the expected improvements in the experimental sensitivity, the μ–e conversion will become the most stringent test for all the involved combinations of couplings.