2,826 research outputs found
The Search for Beauty-fully Bound Tetraquarks Using Lattice Non-Relativistic QCD
Motivated by multiple phenomenological considerations, we perform the first
search for the existence of a tetraquark bound state with a
mass below the lowest non-interacting bottomonium-pair threshold using the
first-principles lattice non-relativistic QCD methodology. We use a full
-wave colour/spin basis for the operators in the three
, and channels. We employ four gluon field ensembles
at multiple lattice spacing values ranging from fm, all of
which include , , and quarks in the sea, and one ensemble which
has physical light-quark masses. Additionally, we perform novel exploratory
work with the objective of highlighting any signal of a near threshold
tetraquark, if it existed, by adding an auxiliary potential into the QCD
interactions. With our results we find no evidence of a QCD bound tetraquark
below the lowest non-interacting thresholds in the channels studied.Comment: 24 Pages; 19 Figures; Accepted By PRD; Unaveraged Correlator Data
Publicly Available in SQLite Databas
The Decay with Highly Improved Staggered Quarks and NRQCD
We report on progress of a lattice QCD calculation of the and
semileptonic form factors. We use a relativistic staggered
action (HISQ) for light and charm quarks, and an improved non-relativistic
(NRQCD) action for bottom, on the second generation MILC ensembles.Comment: Presented at Lattice 2017, the 35th International Symposium on
Lattice Field Theory at Granada, Spain (18-24 June 2017
vector, axial-vector and tensor form factors for the full range from lattice QCD
We compute the complete set of SM and tensor semileptonic form factors across the full kinematic
range of the decay using second generation MILC HISQ gluon field
configurations and HISQ valence quarks, with the heavy-HISQ method. Lattice
spacings range from to with pion masses
from down to the physical value and heavy quark
masses ranging between and ;
currents are normalised nonperturbatively. Using the recent data from Belle and LHCb together with our form
factors we determine a model independent value of
, in agreement
with previous exclusive determinations and in tension with the inclusive result
at the level of . We observe a tension between the
shape of the differential decay rates computed using our form factors and those
measured by Belle. We compute a lattice-only SM value for the ratio of
semitauonic and semimuonic decay rates, , which we find to be
closer to the recent Belle measurement and HFLAV average than theory
predictions using fits to experimental differential rate data for . Determining using the total rate for gives a value in agreement with inclusive results. We compute the
longitudinal polarisation fraction for the semitauonic mode,
, which is in tension at the level of with the
recent Belle measurement. Our calculation combines and lattice results, and we provide an update which supersedes our previous
lattice computation of the form factors. We also give the chiral
perturbation theory needed to analyse the tensor form factors.Comment: 49 pages, 27 figure
Form Factors for the full range from Lattice QCD
We present the first lattice QCD determination of the vector and axial-vector form factors. These will enable experimental
information on the rate for semileptonic decays to to be
converted into a value for . Our calculation covers the full physical
range of the decay and uses non-perturbatively renormalised lattice
currents. We use the Highly Improved Staggered Quark (HISQ) action for all
valence quarks on the second generation MILC ensembles of gluon field
configurations including , , and HISQ sea quarks. Our HISQ heavy
quarks have masses ranging upwards from that of ; we are able to reach that
of the on our finest lattices. This enables us to map out the dependence on
heavy quark mass and determine results in the continuum limit at the . We
use our form factors to construct the differential rates for and obtain a total rate with uncertainty:
. Including values for , and
yields a branching fraction for this decay mode of
0.0150(11)(10)(3) ~with uncertainties from lattice QCD,
and respectively.Comment: 23 pages, 14 Figures, Version accepted for publication in Phys. Rev.
Semileptonic Decay Scalar Form Factor and from Lattice QCD
We present a new study of D semileptonic decays on the lattice which employs
the Highly Improved Staggered Quark (HISQ) action for both the charm and the
light valence quarks. We work with MILC unquenched lattices and
determine the scalar form factor for
semileptonic decays. The form factor is obtained from a scalar current matrix
element that does not require any operator matching. We develop a new approach
to carrying out chiral/continuum extrapolations of . The method uses
the kinematic "" variable instead of or the kaon energy and is
applicable over the entire physical range. We find in the chiral plus
continuum limit and hereby improve the theory error on this quantity by a
factor of 4 compared to previous lattice determinations. Combining the
new theory result with recent experimental measurements of the product from BaBar and CLEO-c leads to the most
precise direct determination of the CKM matrix element to date,
, where the first error comes from experiment and the
second is the lattice QCD theory error. We calculate the ratio and find GeV and show
that this agrees with experiment.Comment: 23 pages, 31 figures, 11 tables. Added a paragraph in sction VII, and
updated with PDG 2010 instead of PDG 200
Semileptonic Decays, and 2 Row Unitarity from Lattice QCD
We present a new calculation of the semileptonic
form factor at based on HISQ charm and
light valence quarks on MILC lattices. Using methods developed
recently for HPQCD's study of decays, we find . 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 , where the first
error comes from experiment and the second from theory. With a total error of
\% the accuracy of direct determination of from
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
, HPQCD's earlier and from the Fermilab Lattice
\& MILC collaborations. We find , improving on the current PDG2010 value.Comment: 7 pages, 7 figures, and 4 table
B and B-s meson decay constants from lattice QCD
We present a new determination of the B and B-s meson decay constants using nonrelativistic quantum chromodynamics (NRQCD) b-quarks, highly improved staggered quark (HISQ) light and strange valence quarks and the MILC collaboration N-f = 2 + 1 lattices. The new calculations improve on HPQCD\u27s earlier work with NRQCD b-quarks by replacing AsqTad with HISQ valence quarks, by including a more chiral MILC fine ensemble in the analysis, and by employing better tuned quark masses and overall scale. We find f (B) = 0.191(9) GeV, f (Bs) = 0.228(10) GeV and f (Bs)/f (B) = 1.188(18). Combining the new value for f (Bs)/f (B) with a recent very precise determination of the B-s meson decay constant based on HISQ b-quarks, f (Bs) = 0.225(4) GeV, leads to f (B) = 0.189(4) GeV. With errors of just 2.1% this represents the most precise f (B) available today
- β¦