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Register a new userImprovement of heavy-heavy and heavy-light currents with the Oktay-Kronfeld action
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The CKM matrix elements $V_{cb}$ and $V_{ub}$ can be obtained by combining data from the experiments with lattice QCD results for the semi-leptonic form factors for the $bar{B} to D^ast ell bar{ u}$ and $bar{B} to pi ell bar{ u}$ decays. It is highly desirable to use the Oktay-Kronfeld (OK) action for the form factor calculation on the lattice, since the OK action is designed to reduce the heavy quark discretization error down to the $mathcal{O}(lambda^4)$ level in the power counting rules of the heavy quark effective theory (HQET). Here, we present a matching calculation to improve heavy-heavy and heavy-light currents up to the $lambda^3$ order in HQET, the same level of improvement as the OK action. Our final results for the improved currents are being used in a lattice QCD calculation of the semi-leptonic form factors for the $bar{B} to D^ast ell bar{ u}$ and $bar{B} to D ell bar{ u}$ decays.
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One-loop matching of heavy-light currents is carried out for a highly improved lattice action, including the effects of dimension 4 O(1/M) and O(a) operators. We use the NRQCD action for heavy quarks, the Asqtad improved naive action for light quarks, and the Symanzik improved glue action. As part of the matching procedure we also present results for the NRQCD self energy and for massless Asqtad quark wavefunction renormalization with improved glue.
We calculate the one loop renormalisation parameters for the heavy-light axial-vector and vector currents using lattice perturbation theory. We use NonRelativistic QCD (NRQCD) heavy quarks and the Highly Improved Staggered Quark (HISQ) action for the light quarks. We present results for heavy-light currents with massless HISQ quarks and briefly discuss the extension to heavy-heavy currents with massive HISQ quarks.
We report recent progress in calculating semileptonic form factors for the $bar{B} to D^ast ell bar{ u}$ and $bar{B} to D ell bar{ u}$ decays using the Oktay-Kronfeld (OK) action for bottom and charm quarks. We use the second order in heavy quark effective power counting $mathcal{O}(lambda^2)$ improved currents in this work. The HISQ action is used for the light spectator quarks. We analyzed four $2+1+1$-flavor MILC HISQ ensembles with $aapprox 0.09,mathrm{fm}$, $0.12,mathrm{fm}$ and $M_pi approx 220,mathrm{MeV}$, $310,mathrm{MeV}$: $a09m220$, $a09m310$, $a12m220$, $a12m310$. Preliminary results for $Bto D^astell u$ decays form factor $h_{A_1}(w)$ at zero recoil ($w=1$) are reported. Preliminary results for $B to D,ell u$ decays form factors $h_pm(w)$ over a kinematic range $1<w<1.3$ are reported as well.
We carry out a perturbative determination of mass dependent renormalization factors and $O(a)$ improvement coefficients for the vector and axial vector currents with a relativistic heavy quark action, which we have designed to control $m_Qa$ errors by extending the on-shell $O(a)$ improvement program to the case of $m_Q gg Lambda_{rm QCD}$ with $m_Q$ the heavy quark mass. We discuss what kind of improvement operators are required for the heavy-heavy and the heavy-light cases under the condition that the Euclidean rotational symmetry is not retained anymore because of the $m_Qa$ corrections. Our calculation is performed employing the ordinary perturbation theory with the fictitious gluon mass as an infrared regulator. We show that all the improvement coefficients are determined free from infrared divergences. Results of the renormalization factors and the improvement coefficients are presented as a function of $m_Q a$ for various improved gauge actions as well as the plaquette action.
We present results on an analysis of the decay constants f_B and f_Bs with two flavours of sea quark. The calculation has been carried out on 3 different bare gauge couplings and 4 sea quark masses at each gauge coupling, with m_pi/m_rho ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform calculations with heavy quarks whose mass is in the range of the b-quark. A detailed comparison with a quenched calculation using the same action is made to elucidate the effects due to the sea quarks.
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