By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb-1 collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the D+→ημ+νμ decay to be BD+→ημ+νμ=(10.4±1.0stat±0.5syst)×10-4. Using the world averaged value of BD+→ηe+νe, the ratio of the two branching fractions is determined to be BD+→ημ+νμ/BD+→ηe+νe=0.91±0.13(stat+syst), which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor f+η(0) and the c→d Cabibbo-Kobayashi-Maskawa matrix element |Vcd| to be f+η(0)|Vcd|=0.087±0.008stat±0.002syst. Taking the input of |Vcd| from the global fit in the standard model, we determine f+η(0)=0.39±0.04stat±0.01syst. On the other hand, using the value of f+η(0) calculated in theory, we find |Vcd|=0.242±0.022stat±0.006syst±0.033theory.
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. 11775230, No. 11475123, No. 11625523, No. 11635010, No. 11735014, No. 11822506, No. 11835012, No. 11935015, No. 11935016, No. 11935018, No. and 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. U1532101, No. U1932102, No. U1732263, and No. U1832207; CAS Key Research Program of Frontier Sciences under Contracts No. QYZDJ-SSW-SLH003 and No. QYZDJ-SSW-SLH040; 100 Talents Program of CAS; 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 and No. DE-SC-0012069.
© 2020 authors.
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