Search for Lepton Flavor Violation in ${\rm Y}(3S)\to e^{\pm }{\mu }^{\mp }$

Abstract

We report on the first search for electron-muon lepton flavor violation (LFV) in the decay of a $b$~quark and $b$~antiquark bound state. We look for the LFV decay ${\rm Y}(3S)\to e^{\pm }{\mu }^{\mp }$ in a sample of 118~million ${\rm Y}(3S)$ mesons from 27~fb${}^{-1}$ of data collected with the \babar\ detector at the SLAC PEP-II $e^{+}{e}^{-}$ collider operating with a 10.36~GeV center-of-mass energy. No evidence for a signal is found and we set a limit on the branching fraction $\mathcal{B}({\rm Y}(3S)\to e^{\pm }{\mu }^{\mp })<3.6\times 10^{-7}\mathrm{at}90\%\mathrm{CL}$. This result can be interpreted as a limit ${\Lambda }_{NP}/g_{NP}^2>80$TeV on the energy scale ${\Lambda }_{NP}$ divided by the coupling-squared $g_{NP}^2$ of relevant new physics.

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• The lepton flavor violating decays of vector mesons in the MRSSM