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We report on a precision measurement of the ratio Rϒð3SÞ τμ ¼ Bðϒð3SÞ → τþτ−Þ=Bðϒð3SÞ → μþμ−Þ using data collected with the BABAR detector at the SLAC PEP-II eþe− collider. The measurement is based on a 28 fb−1 data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million ϒð3SÞ mesons. The ratio is measured to be Rϒð3SÞ τμ ¼ 0.966 0.008stat 0.014syst and is in agreement with the standard model prediction of 0.9948 within 2 standard deviations. The uncertainty in Rϒð3SÞ τμ is almost an order of magnitude smaller than the only previous measurement.

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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

APA Citation

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. (2020). Precision measurement of the ratio . Physical Review Letters, 125(24).

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