Lattice Study of the Decaȳ

We present the final analysis of the light and strange hadron spectra from a full QCD lattice simulation with two degenerate dynamical sea quark flavours at β = 5.6 on a 16 3 × 32 lattice. Four sets of sea quark masses corresponding to the range .69 ≤ m π /m ρ ≤ .83 are investigated. For reference we also ran a quenched simulation at β eff = 6.0, which is the point of equal lattice spacing, a −1 ρ . In the light sector, we find the chiral extrapolation to physical u-and d-masses to present a major source of uncertainty, comparable to the expected size of unquenching effects. From linear and quadratic fits we can estimate the errors on the hadron masses made from light quarks to be on a 15 % level prior to the continuum extrapolation. For the hadrons with strange valence quark content, the N F = 2 approximation to QCD appears not to cure the well-known failure of quenched QCD to reproduce the physical K − K * splitting.2

We present results of a lattice computation of the matrix elements of the vector and axial-vector currents which are relevant for the semileptonic decays D -+ K and D + K*. The computations are performed in the quenched approximation to lattice QCD on a 243 x 48 lattice at = 6.2, using an O(a)-improved fermionic action. In the limit of zero lepton masses the semileptonic decays D + K and D + K* are described by four form factors: f s , V, A1, and Ap, which are functions of q 2 , where --qF is the four-momentum transferred in the process. Our results for these form factors at q 2 = 0 are f 2 ( 0 ) = 0.67' :, V(0) = 1.01?::, Al(0) = 0.70?:,, Az(0) = 0.66+:0,, which are consistent with the most recent experimental world average values. We have also determined the q2 dependence of the form factors, which we find to be reasonably well described by a simple pole-dominance model.Results for other form factors, including those relevant to the decays D -+ T and D -+ p, are also given.PACS number(s): 13.20.Fc, 12.38.G~

We present a study of semi-leptonicB → Dℓν decays in quenched lattice QCD through a calculation of the matrix element D|cγ µ b|B on a 24 3 × 48 lattice at β = 6.2, using an O (a)-improved fermion action. We perform the calculation for several values of the initial and final heavy-quark masses around the charm mass, and three values of the light-(anti)quark mass around the strange mass. Because the charm quark has a bare mass which is almost 1/3 the inverse lattice spacing, we study the ensuing mass-dependent discretization errors, and propose a procedure for subtracting at least some of them non-perturbatively. * Present address: HLRZ, 52425 Jülich, Germany † Present address: Dept. of Physics and Astronomy, The University, Glasgow G12 8QQ, Scotland ‡ Present address: FNAL, PO Box 500, Batavia IL 60510, USA § Unité Propre de Recherche 7061. 1We extract the form factors h + and h − . After radiative corrections, we find that h + displays no dependence on the heavy-quark mass, enabling us to identify it with an Isgur-Wise function ξ. Interpolating the light-quark mass to that of the strange, we obtain an Isgur-Wise function relevant for − 2 (syst.) at zero recoil. We observe a slight decrease in the magnitude of the central value of the slope as the mass of the light quark is reduced; given the errors, however, the significance of this observation is limited.We then use these functions, in conjunction with heavy-quark effective theory, to extract V cb with no free parameters from theB → D * ℓν decay rate measured by the ALEPH, ARGUS and CLEO collaborations. Using the CLEO data, for instance, we obtain |V cb | = 0.037, where δ 1/m 2 c is the power correction inversely proportional to the square of the charm quark mass, and β A 1 (1) is the relevant radiative correction at zero recoil. Here, the first set of errors is experimental, the second represents the statistical error and the third represents the systematic error in our evaluation of the Isgur-Wise function. We also use our Isgur-Wise functions and heavyquark effective theory to calculate branching ratios forB (s)

We present a lattice calculation of the interquark potential between static quarks in a "full" QCD simulation with 2 flavours of dynamical Wilson-quarks at three intermediate sea-quark masses. We work at β = 5.6 on lattice size of 16 3 × 32 with 100 configurations per sea-quark mass. We compare the full QCD potential with its quenched counterpart at equal lattice spacing, a −1 ≃ 2.0 GeV, which is at the onset of the quenched scaling regime. We find that the full QCD potential lies consistently below that of quenched QCD. We see no evidence for string-breaking effects on these lattice volumes, V ≃ (1.5 fm) 3 .