First Observation of D+ -> eta mu(+)nu(mu) and Measurement of Its Decay Dynamics

Abstract

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+ -> eta mu(+) nu(mu) decay to be BD+ ->eta mu+nu mu = (10.4 +/- 1.0(stat) +/- 0.5(syst)) x 10(-4). Using the world averaged value of BD+ ->eta e+nu e, the ratio of the two branching fractions is determined to be = BD+ ->eta mu+nu mu/BD+ ->eta e+nu e =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(+)(eta)(0) and the c -> d Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cd vertical bar to be f(+)(eta)(0)vertical bar V-cd vertical bar = 0.087 +/- 0.008(stat) +/- 0.002(syst). Taking the input of vertical bar V-cd vertical bar from the global fit in the standard model, we determine f(+)(eta)(0) = 0.39 +/- 0.04(stat) +/- 0.01(syst). On the other hand, using the value of f(+)(eta)(0) calculated in theory, we find vertical bar V-cd vertical bar= 0.242 +/- 0.022(stat )+/- 0.006(syst) +/- 0.033(theory).