Improved Measurement Of The Absolute Branching Fraction Of (?)

Experimental studies of D semileptonic decays provide helpful information to understand D decay mechanisms.Their decay branching fractions(Br) can serve to test isospin conservation and leptonic universality in D semileptonic decays.Isospin conservation implies that the partial widths of D0â†'K-μ+vμ and D+â†'Kμ+vμ should be equal.Furthermore,Γ(D+â†'K0μ+vμ) is predicted to be less than Γ(D+ â†'K0e+ve) by about 3% due to different form factors and phase space.Using the branching fractions and the lifetimes of the D0 and D+ mesons(Ï„D0,Ï„D+),quoted from the Particle Data Group,we obtain Γ(D0â†'K-μ+vμ)/Γ(D+â†'K0μ+vμ)=0.91 ±0.07 and Γ(D+â†'K0μ+vμ/Γ(D+â†'K0e+ve)=1.04±0.07,where the uncertainties are dominated by Br(D+â†'K0μ+vμ).Thus,an improved measurement of Br(D+â†'K0μ+vμ) will be helpful to understand D decay mechanisms with better accuracy.In addition,the improved B(D+â†'K0μ+vμ) can also be used to precisely determine the form factor f+k(0) and the quark mixing matrix element |Vcs| from D semileptonic decays.By analyzing 2.93 fb-1 of data collected at (?)=3.773 GeV with the BES-â…¢ detector,we measure the absolute branching fraction Br(D+â†'Kμ+vμ)=(8.72± 0.07stst.±0.18sys.)%,which is consistent with previous measurements within errors but with significantly improved precision.Combining the Particle Data Group values for Br(D0â†'K-μ+vμ),Br(D+â†'Ke+ve),and the lifetimes of the D0 and D+ mesons with the value of Br(D+â†'Kμ+vμ)measured in this work,we determine the following ratios of partial widths:Γ(D0â†'K-μ+vμ)/Γ(D+â†'K0μ+vμ)=0.963 ±0.044 and Γ(D+â†'K0μ+vμ)/Γ(D+â†'K0e+ve)=0.988±0.033.These provide important information for testing the isospin conservation and the leptonic universality assumption in the exclusive semi-muonic decays of D mesons.