We report the first observation of the semimuonic decay D+→ωμ+νμ using an e+e- collision data sample corresponding to an integrated luminosity of 2.93 fb-1 collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. The absolute branching fraction of the D+→ωμ+νμ decay is measured to be BD+→ωμ+νμ=(17.7±1.8stat±1.1syst)×10-4. Its ratio with the world average value of the branching fraction of the D+→ωe+νe decay probes lepton flavor universality and it is determined to be BD+→ωμ+νμ/BD+→ωe+νePDG=1.05±0.14, in agreement with the standard model expectation within one standard deviation.
Bibliographical noteFunding Information:
The BESIII collaboration thanks the staff of BEPCII and the IHEP computing center for their strong support. This work is supported in part by National Key Basic Research Program of China under Contract No. 2015CB856700; National Natural Science Foundation of China (NSFC) under Contracts No. 11675200, No. 11625523, No. 11635010, No. 11735014, No. 11822506, No. 11835012, No. 11961141012; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts No. U1632109, No. U1532257, No. U1532258, No. U1732263, No. U1832207; CAS Key Research Program of Frontier Sciences under Contracts No. QYZDJ-SSW-SLH003, No. QYZDJ-SSW-SLH040; 100 Talents Program of CAS; Institute of Nuclear and Particle Physics, Astronomy and Cosmology (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; ERC under Contract No. 758462; German Research Foundation DFG under Contracts No. Collaborative Research Center CRC 1044 and No. FOR 2359; Istituto Nazionale di Fisica Nucleare, Italy; Ministry of Development of Turkey under Contract No. DPT2006K-120470; National Science and Technology fund; STFC (United Kingdom); The Knut and Alice Wallenberg Foundation (Sweden) under Contract No. 2016.0157; The Royal Society, UK under Contracts No. DH140054 and No. DH160214; The Swedish Research Council; U.S. Department of Energy under Contracts No. DE-FG02-05ER41374, No. DE-SC-0010118, No. DE-SC-0012069.
© 2020 authors. Published by the American Physical Society.