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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 ϒ(3S) → e ± μ in a sample of 118 million ϒ(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 B[ϒ(3S) → e ± μ]< 3.6 × 10−7 at 90% C. L. This result can be interpreted as a limit ΛNP=g2NP > 80 TeV on the energy scale ΛNP divided by the coupling-squared g2NP of relevant new physics (NP).

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Lees, J. P., Poireau, V., Tisserand, V., Grauges, E., Palano, A., Eigen, G., Brown, D. N., Kolomensky, Yu. G., Fritsch, M., Koch, H., Schroeder, T., Cheaib, R., Hearty, C., Mattison, T. S., McKenna, J. A., So, R. Y., Blinov, V. E., Buzykaev, A. R., Druzhinin, V. P., … Wu, S. L. (2022b). Search for lepton flavor violation in . Physical Review Letters, 128(9).

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