42 research outputs found

### Diquark Representations for Singly Heavy Baryons with Light Staggered Quarks

In the staggered fermion formulation of lattice QCD, we construct diquark
operators which are to be embedded in singly heavy baryons. The group
theoretical connections between continuum and lattice staggered diquark
representations are established.Comment: v1, 13 pages with title "Staggered Diquarks for Singly Heavy
Baryons"; v2, 4 pages in revtex, changed the title to be more specifi

### $B_s \to K \ell \nu$ form factors from lattice QCD

We report the first lattice QCD calculation of the form factors for the
standard model tree-level decay $B_s\to K \ell\nu$. In combination with future
measurement, this calculation will provide an alternative exclusive
semileptonic determination of $|V_{ub}|$. We compare our results with previous
model calculations, make predictions for differential decay rates and branching
fractions, and predict the ratio of differential branching fractions between
$B_s\to K\tau\nu$ and $B_s\to K\mu\nu$. We also present standard model
predictions for differential decay rate forward-backward asymmetries,
polarization fractions, and calculate potentially useful ratios of $B_s\to K$
form factors with those of the fictitious $B_s\to\eta_s$ decay. Our lattice
simulations utilize NRQCD $b$ and HISQ light quarks on a subset of the MILC
Collaboration's $2+1$ asqtad gauge configurations, including two lattice
spacings and a range of light quark masses.Comment: 24 pages, 21 figures; Ver. 2 matches published versio

### BβDlΞ½ form factors at nonzero recoil and extraction of |Vcb|

We present a lattice QCD calculation of the BβDlΞ½ 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(BβDΟΞ½Ο)/B(BβDlΞ½l) (l=e,ΞΌ). We find |Vcb|BβDexcl=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)

### $B_s \to D_s \ell \nu$ Form Factors and the Fragmentation Fraction Ratio $f_s/f_d$

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