|Vcd| from D Meson Leptonic Decays
Abstract
We present an update of the D meson decay constant fD using the Highly Improved Staggered Quark (HISQ) action for valence charm and light quarks on MILC Nf = 2+1 lattices. The new determination incorporates HPQCD's improved scale r1Nf = 2+1 = 0.3133(23) fm, accurately retuned bare charm quark masses and data from an ensemble that is more chiral than in our previous calculations. We find fD = 208.3(3.4) MeV. Combining the new fD with D -> μ \ branching fraction data from CLEO-c, we extract the CKM matrix element |Vcd| = 0.223(10)exp.(4)lat.. This value is in excellent agreement with |Vcd| from D semileptonic decays and from neutrino scattering experiments and has comparable total errors. We determine the ratio between semileptonic form factor and decay constant and find [fD -> π+(0) / fD ]lat. = 3.20(15) GeV-1 to be compared with the experimental value of [fD -> π+(0) / fD ]exp. = 3.19(18) GeV-1. Finally, we mention recent preliminary but already more accurate D -> μ \ branching fraction measurements from BES III and discuss their impact on precision |Vcd| determinations in the future.
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