Charm semileptonic decays and |V_{cs(d)}| from heavy clover quarks and   2+1 flavor asqtad staggered ensembles
  By combining experimentally measured partial branching fractions for the semileptonic decays D to K l nu and D to pi l nu with lattice calculations of the form factors f_+^{D to K}(q^2) and f_+^{D to pi}(q^2), one can extract the CKM matrix elements |V_{cs}| and |V_{cd}|. We are calculating the form factors by using Fermilab charm and asqtad staggered light and strange quarks on 2+1 flavor asqtad staggered ensembles generated by the MILC Collaboration. We vary the light valence quark masses from 0.4m_s to 0.05m_s (m_s is the strange sea-quark mass), and the lattice spacings, from about 0.12 fm to about 0.045 fm. We extrapolate to the physical light-quark mass and the continuum limit using heavy-light meson staggered chiral perturbation theory about the SU(2) and SU(3) limits, compare the resulting (preliminary) form factor shapes with experiment, and discuss our errors. 
Jon A. Bailey, D. Du, A. X. El-Khadra, Steven Gottlieb, R. D. Jain, A.   S. Kronfeld, R. S. Van de Water, and R. Zhou (for t...
hep-lat