D→K, lν semileptonic decay scalar form factor and |V_cs| from lattice QCD
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Date
2010-12-09
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American Physical Society
Abstract
We present a new study of D semileptonic decays on the lattice which employs the highly improved staggered quark action for both the charm and the light valence quarks. We work with MILC unquenched N_f=2+1 lattices and determine the scalar form factor f_0(q^2) for D→K, lν semileptonic decays. The form factor is obtained from a scalar current matrix element that does not require any operator matching. We develop a new approach to carrying out chiral/continuum extrapolations of f_0(q^2). The method uses the kinematic "z" variable instead of q^2 or the kaon energy E_K and is applicable over the entire physical q^2 range. We find f_0^D→K(0)≡f_+^D→K(0)=0.747(19) in the chiral plus continuum limit and hereby improve the theory error on this quantity by a factor of ∼4 compared to previous lattice determinations. Combining the new theory result with recent experimental measurements of the product f_+^D→K(0)*|V_cs| from BABAR and CLEO-c leads to a very precise direct determination of the CKM matrix element |V_cs|, |V_cs|=0.961(11)(24), where the first error comes from experiment and the second is the lattice QCD theory error. We calculate the ratio f_+^D→K(0)/f_Ds and find 2.986±0.087 GeV^-1 and show that this agrees with experiment.
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Citation
Heechang Na et al, "D→K, lν semileptonic decay scalar form factor and |V_cs| from lattice QCD," Physical Review D 82, no. 11 (2010), doi:10.1103/PhysRevD.82.114506