D→KlνD \rightarrow Kl{\nu} semileptonic decay using lattice QCD with HISQ at physical pion masses

The quark flavor sector of the Standard Model is a fertile ground to look for new physics effects through a unitarity test of the Cabbibo-Kobayashi-Maskawa (CKM) matrix. We present a lattice QCD calculation of the scalar and the vector form factors (over a large $q^2$ region including $q^2 = 0$) associated with the $D \rightarrow Kl{\nu}$ semi-leptonic decay. This calculation will then allow us to determine the central CKM matrix element, $V_{cs}$ in the Standard Model, by comparing the lattice QCD results for the form factors and the experimental decay rate. This form factor calculation has been performed on the $N_f =2+1+1$ MILC HISQ ensembles with the physical light quark masses.Comment: Proceedings for the 35th International Symposium on Lattice Field Theory (Lattice 2017), 8 pages, 5 figure

Light meson form factors at high Q2Q^2 from lattice QCD

Measurements and theoretical calculations of meson form factors are essential for our understanding of internal hadron structure and QCD, the dynamics that bind the quarks in hadrons. The pion electromagnetic form factor has been measured at small space-like momentum transfer $|q^2| < 0.3$~GeV$^2$ by pion scattering from atomic electrons and at values up to $2.5$~GeV$^2$ by scattering electrons from the pion cloud around a proton. On the other hand, in the limit of very large (or infinite) $Q^2=-q^2$, perturbation theory is applicable. This leaves a gap in the intermediate $Q^2$ where the form factors are not known. As a part of their 12 GeV upgrade Jefferson Lab will measure pion and kaon form factors in this intermediate region, up to $Q^2$ of $6$~GeV$^2$. This is then an ideal opportunity for lattice QCD to make an accurate prediction ahead of the experimental results. Lattice QCD provides a from-first-principles approach to calculate form factors, and the challenge here is to control the statistical and systematic uncertainties as errors grow when going to higher $Q^2$ values. Here we report on a calculation that tests the method using an $\eta_s$ meson, a 'heavy pion' made of strange quarks, and also present preliminary results for kaon and pion form factors. We use the $n_f=2+1+1$ ensembles made by the MILC collaboration and Highly Improved Staggered Quarks, which allows us to obtain high statistics. The HISQ action is also designed to have small discretisation errors. Using several light quark masses and lattice spacings allows us to control the chiral and continuum extrapolation and keep systematic errors in check.Comment: Presented at Lattice 2017, the 35th International Symposium on Lattice Field Theory at Granada, Spain (18-24 June 2017

Nonperturbative tests of the renormalization of mixed clover-staggered currents in lattice QCD

The Fermilab Lattice and MILC collaborations have shown in one-loop lattice QCD perturbation theory that the renormalization constants of vector and axial-vector mixed clover-asqtad currents are closely related to the product of those for clover-clover and asqtad-asqtad (local) vector currents. To be useful for future higher precision calculations this relationship must be valid beyond one-loop and very general. We test its validity nonperturbatively using clover and Highly Improved Staggered (HISQ) strange quarks, utilising the absolute normalization of the HISQ temporal axial current. We find that the renormalization of the mixed current differs from the square root of the product of the pure HISQ and pure clover currents by 2−3%. We also compare discretization errors between the clover and HISQ formalisms

Precision tests of the J/psi from full lattice QCD: mass, leptonic width and radiative decay rate to eta_c

We show results from calculations in full lattice QCD of the mass, leptonic width and radiative decay rate to eta_c of the J/psi meson. These provide few % tests of QCD. Another (1.5%) test comes from comparison of time-moments of the vector charmonium correlator with results derived from the experimental values of R(e+e- to hadrons) in the charm region

D→π,lνD \rightarrow \pi, l \nu Semileptonic Decays, ∣Vcd∣|V_{cd}| and 2nd^{nd} Row Unitarity from Lattice QCD

We present a new calculation of the $D \rightarrow \pi, l \nu$ semileptonic form factor $f^{D \rightarrow \pi}_+(q^2)$ at $q^2 = 0$ based on HISQ charm and light valence quarks on MILC $N_f = 2 +1$ lattices. Using methods developed recently for HPQCD's study of $D \rightarrow K, l \nu$ decays, we find $f^{D \rightarrow \pi}_+(0) = 0.666(29)$. This signifies a better than factor of two improvement in errors for this quantity compared to previous calculations. Combining the new result with CLEO-c branching fraction data, we extract the CKM matrix element $|V_{cd}| = 0.225(6)_{exp.}(10)_{lat.}$, where the first error comes from experiment and the second from theory. With a total error of $\sim5.3$\% the accuracy of direct determination of $|V_{cd}|$ from $D$ semileptonic decays has become comparable to (and in good agreement with) that from neutrino scattering. We also check for second row unitarity using this new $|V_{cd}|$, HPQCD's earlier $|V_{cs}|$ and $|V_{cb}|$ from the Fermilab Lattice \& MILC collaborations. We find $|V_{cd}|^2 + |V_{cs}|^2 + |V_{cb}|^2 = 0.976(50)$, improving on the current PDG2010 value.Comment: 7 pages, 7 figures, and 4 table

Heavy-light current-current correlators

The current-current correlator method has been used successfully to obtain very accurate results for quark masses and the coupling alpha_s. The calculations were done using Highly Improved Staggered Quarks (HISQ) and heavy-heavy meson correlators. We now extend this work to the significantly more challenging heavy-light case, reporting the first results here. The aim is to determine nonperturbative Z factors for NRQCD heavy-light currents, but first we test the method in the HISQ case where Z=1.Comment: 7 pages. Presented at the XXVIII International Symposium on Lattice Field Theory (Lattice 2010), June 14-19 2010, Villasimius, Ital