B→Dlν form factors at nonzero recoil and extraction of |Vcb|

We present a lattice QCD calculation of the B→Dlν semileptonic decay form factors f+(q2) and f0(q2) for the entire physical q2 range. Nonrelativistic QCD bottom quarks and highly improved staggered quark charm and light quarks are employed together with Nf=2+1 MILC gauge configurations. A joint fit to our lattice and BABAR experimental data allows an extraction of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb|. We also determine the phenomenologically interesting ratio R(D)=B(B→Dτντ)/B(B→Dlνl) (l=e,μ). We find |Vcb|B→Dexcl=0.0402(17)(13), where the first error consists of the lattice simulation errors and the experimental statistical error and the second error is the experimental systematic error. For the branching fraction ratio we find R(D)=0.300(8)

Matrix Elements From Moments of Correlation Functions

Momentum-space derivatives of matrix elements can be related to their coordinate-space moments through the Fourier transform. We derive these expressions as a function of momentum transfer Q^2 for asymptotic in/out states consisting of a single hadron. We calculate corrections to the finite volume moments by studying the spatial dependence of the lattice correlation functions. This method permits the computation of not only the values of matrix elements at momenta accessible on the lattice, but also the momentum-space derivatives, providing a priori information about the Q^2 dependence of form factors. As a specific application we use the method, at a single lattice spacing and with unphysically heavy quarks, to directly obtain the slope of the isovector form factor at various Q^2, whence the isovector charge radius. The method has potential application in the calculation of any hadronic matrix element with momentum transfer, including those relevant to hadronic weak decays

B and Bs semileptonic decay form factors with NRQCD/HISQ quarks

We discuss our ongoing effort to calculate form factors for several B and Bs semileptonic decays. We have recently completed the first unquenched calculation of the form factors for the rare decay B -> K ll. Extrapolated over the full kinematic range of q^2 via model-independent z expansion, these form factor results allow us to calculate several Standard Model observables. We compare with experiment (Belle, BABAR, CDF, and LHCb) where possible and make predictions elsewhere. We discuss preliminary results for Bs -> K l nu which, when combined with anticipated experimental results, will provide an alternative exclusive determination of |Vub|. We are exploring the possibility of using ratios of form factors for this decay with those for the unphysical decay Bs -> eta_s as a means of significantly reducing form factor errors. We are also studying B -> pi l nu, form factors for which are combined with experiment in the standard exclusive determination of |Vub|. Our simulations use NRQCD heavy and HISQ light valence quarks on the MILC 2+1 dynamical asqtad configurations.Comment: 7 pages, 5 figures, presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German

Bs→DsℓνB_s \to D_s \ell \nu Form Factors and the Fragmentation Fraction Ratio fs/fdf_s/f_d

We present a lattice quantum chromodynamics determination of the scalar and vector form factors for the $B_s \rightarrow D_s \ell \nu$ decay over the full physical range of momentum transfer. In conjunction with future experimental data, our results will provide a new method to extract $|V_{cb}|$, which may elucidate the current tension between exclusive and inclusive determinations of this parameter. Combining the form factor results at non-zero recoil with recent HPQCD results for the $B \rightarrow D \ell \nu$ form factors, we determine the ratios $f^{B_s \rightarrow D_s}_0(M_\pi^2) / f^{B \rightarrow D}_0(M_K^2) = 1.000(62)$ and $f^{B_s \rightarrow D_s}_0(M_\pi^2) / f^{B \rightarrow D}_0(M_\pi^2) = 1.006(62)$. These results give the fragmentation fraction ratios $f_s/f_d = 0.310(30)_{\mathrm{stat.}}(21)_{\mathrm{syst.}}(6)_{\mathrm{theor.}}(38)_{\mathrm{latt.}}$ and $f_s/f_d = 0.307(16)_{\mathrm{stat.}}(21)_{\mathrm{syst.}}(23)_{\mathrm{theor.}}(44)_{\mathrm{latt.}}$, respectively. The fragmentation fraction ratio is an important ingredient in experimental determinations of $B_s$ meson branching fractions at hadron colliders, in particular for the rare decay ${\cal B}(B_s \rightarrow \mu^+ \mu^-)$. In addition to the form factor results, we make the first prediction of the branching fraction ratio $R(D_s) = {\cal B}(B_s\to D_s\tau\nu)/{\cal B}(B_s\to D_s\ell\nu) = 0.301(6)$, where $\ell$ is an electron or muon. Current experimental measurements of the corresponding ratio for the semileptonic decays of $B$ mesons disagree with Standard Model expectations at the level of nearly four standard deviations. Future experimental measurements of $R(D_s)$ may help understand this discrepancy.Comment: 21 pages, 15 figure

Using B-IBI to Identify Puget Sound Watersheds for Restoration and Protection

More than 20 organizations throughout Puget Sound have active biomonitoring programs to assess stream condition using the Benthic Index of Biotic Integrity (B-IBI). There has been a net decline in the biological condition of small Puget Sound streams since 2007 as shown by B-IBI scores, a Puget Sound Partnership (PSP) vital sign indicator. King County has been awarded funds from the Washington Department of Ecology to identify and prioritize streams for protection and restoration, addressing two PSP Action Agenda recovery targets. This project will develop a decision framework for prioritizing restoration work, and will develop strategies and cost estimates to (1) preserve drainages with “excellent” B-IBI scores and (2) restore 30 drainages from “fair” to “good” B-IBI scores. Based on B-IBI scores from nearly 1,200 sites sampled between 1994 and 2013, 119 sites scored “excellent” one or more times, but only 28 sites averaged “excellent”. 642 sites scored “fair” one or more times and 452 sites averaged “fair”. Proposed criteria such as watershed urbanization, basin area, forest fragmentation and other factors will be presented for prioritizing and choosing which 30 streams or basins to restore from “fair” to “good”. This prioritization process will give local jurisdictions the greatest chance for implementing successful restoration and preservation actions that improve stream condition as measured by B-IBI

B - \u3e Dl nu form factors at nonzero recoil and extraction of vertical bar V-cb vertical bar

We present a lattice QCD calculation of the B -\u3e Dl nu semileptonic decay form factors f(+)(q(2)) and f(0)(q(2)) for the entire physical q(2) range. Nonrelativistic QCD bottom quarks and highly improved staggered quark charm and light quarks are employed together with N-f = 2 + 1 MILC gauge configurations. A joint fit to our lattice and BABAR experimental data allows an extraction of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar. We also determine the phenomenologically interesting ratio R(D) = B(B -\u3e D tau nu(tau))/B(B -\u3e Dl nu(l)) (l = e, mu). We find vertical bar V-cb vertical bar(B -\u3e D)(excl) = 0.0402(17)(13), where the first error consists of the lattice simulation errors and the experimental statistical error and the second error is the experimental systematic error. For the branching fraction ratio we find R(D) = 0.300(8)

Rare decay B -> K ll form factors from lattice QCD

We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay B -> Kll in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks, the highly improved staggered quark formulation for the light valence quarks, and employs the MILC 2+1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q^2. We construct the ratios f0/f+ and fT/f+, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables.Comment: 30 pages, 23 figures; v2 adds a reference and fixes typos, results unchanged; v3 corrects a typo, updates references, makes minor changes in title and text, and is version published in Phys.Rev.D, results unchange

An accurate calculation of the nucleon axial charge with lattice QCD

We report on a lattice QCD calculation of the nucleon axial charge, $g_A$, using M\"{o}bius Domain-Wall fermions solved on the dynamical $N_f=2+1+1$ HISQ ensembles after they are smeared using the gradient-flow algorithm. The calculation is performed with three pion masses, $m_\pi\sim\{310,220,130\}$ MeV. Three lattice spacings ($a\sim\{0.15,0.12,0.09\}$ fm) are used with the heaviest pion mass, while the coarsest two spacings are used on the middle pion mass and only the coarsest spacing is used with the near physical pion mass. On the $m_\pi\sim220$ MeV, $a\sim0.12$ fm point, a dedicated volume study is performed with $m_\pi L \sim \{3.22,4.29,5.36\}$. Using a new strategy motivated by the Feynman-Hellmann Theorem, we achieve a precise determination of $g_A$ with relatively low statistics, and demonstrable control over the excited state, continuum, infinite volume and chiral extrapolation systematic uncertainties, the latter of which remains the dominant uncertainty. Our final determination at 2.6\% total uncertainty is $g_A = 1.278(21)(26)$, with the first uncertainty including statistical and systematic uncertainties from fitting and the second including model selection systematics related to the chiral and continuum extrapolation. The largest reduction of the second uncertainty will come from a greater number of pion mass points as well as more precise lattice QCD results near the physical pion mass.Comment: 17 pages + 11 pages of references and appendices. 15 figures. Interested readers can download the Python analysis scripts and an hdf5 data file at https://github.com/callat-qcd/project_gA_v