Measurement of the absolute branching fractions for purely leptonic Ds+ decays

作者：Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Aliberti, R.; Amoroso, A.; An, M. R.; An, Q.; Bai, X. H.; Bai, Y.; Bakina, O.; Ferroli, R. Baldini; Balossino, I; Ban, Y.; Begzsuren, K.; Berger, N.; Bertani, M.; Bettoni, D.; Bianchi, F.; Bloms, J.; Bortone, A.; Boyko, I; Briere, R. A.; Cai, H.; Cai, X.; Calcaterra, A.; Cao, G. F.; Cao, N.; Cetin, S. A.; Chang, J. F.; Chang, W. L.; Chelkov, G.; Chen, D. Y.; Chen, G.; Chen, H. S.; Chen, M. L.; Chen, S. J.; Chen, X. R.

来源：Physical Review D, 2021, 104(5): 052009.

DOI：10.1103/PhysRevD.104.052009

We report new measurements of the branching fraction B(Dv), where lis either mu or tau (-> pi), based on 6.32 fbof electron-positron annihilation data collected by the BESIII experiment at six center-of-mass energy points between 4.178 and 4.226 GeV. Simultaneously floating the Ds -> mu mu components yields B(D -> tau) = (5.21 +/- 0.25 +/- 0.17) x 102, B(D -> mu mu) (5.35 +/- 0.13 +/- 0.16) x 103, and the ratio of decay widths R = Gamma(D -> tau tau)/Gamma -> mu&m)= 9.73-0.58 +/- 0.36, where the first uncertainties are statistical and the second systematic. No evidence of CP asymmetry is observed in the decay rates Ds +/- -> mu +/- v mu and D +/- -> tau +/-= (+2.9 +/- 4.8 +/- 1.0)%. Constraining our measurement to the Standard Model expectation of lepton universality (R = 9.75), we find the more precise results B(D -> tau = (5.22 +/- 0.10 +/- 0.14) x 10-2and A(+/-) = (-0.1 +/- 1.9 +/- 1.0)%. Combining our results with inputs external to our analysis, we determine the C -> (S) over bar quark mixing matrix element, D+ decay constant, and ratio of the decay constants to be vertical bar V vertical bar = 0.973 +/- 0.009 +/- 0.014, f D+ = 249.9 +/- 2.4 +/- 3.5 MeV, and f D+ / f D = 1.232 +/- 0.035, respectively.