525 research outputs found
Charm and Bottom Quark Masses from Perturbative QCD
Using a new result for the first moment of the hadronic production cross
section at order , and new data on the and
resonances for the charm quark, we determine the \msb masses of the
charm and bottom quarks to be GeV and
GeV. We assume that the continuum
contribution to the sum rules is adequately described by pQCD. While we observe
a large reduction of the perturbative error, the shifts induced by the
theoretical input are very small. The main change in the central value of
is related to the experimental data. On the other hand, the value of is
not changed by our calculation to the assumed precision.Comment: 5 pages, 2 figures, final version as publishe
The heavy quark's self energy from moving NRQCD on the lattice
We present a calculation of the heavy quark's self energy in moving NRQCD to
one-loop in perturbation theory. Results for the energy shift and external
momentum renormalisation are discussed and compared with non-perturbative
results. We show that the momentum renormalisation is small, which is the
result of a remnant of re-parameterisation invariance on the lattice.Comment: Talk given at Lattice2004(heavy), Fermilab, June 21-26, 200
The second moment of the pion's distribution amplitude
We present preliminary results for the second moment of the pion's
distribution amplitude. The lattice formulation and the phenomenological
implications are briefly reviewed, with special emphasis on some subtleties
that arise when the Lorentz group is replaced by the hypercubic group. Having
analysed more than half of the available configurations, the result obtained is
\xi^2_L = 0.06 \pm 0.02.Comment: Lattice 99 (matrix elements), 3 page
Charm as a domain wall fermion in quenched lattice QCD
We report a study describing the charm quark by a domain-wall fermion (DWF)
in lattice quantum chromodynamics (QCD). Our study uses a quenched gauge
ensemble with the DBW2 rectangle-improved gauge action at a lattice cutoff of
GeV. We calculate masses of heavy-light (charmed) and
heavy-heavy (charmonium) mesons with spin-parity and ,
leptonic decay constants of the charmed pseudoscalar mesons ( and ),
and the - mixing parameter. The charm quark mass is found to be
GeV. The mass splittings in
charmed-meson parity partners and are
degenerate within statistical errors, in accord with experiment, and they
satisfy a relation , also consistent with
experiment. A C-odd axial vector charmonium state, \chi_{c1}m_{h_{c}} = 3533(11)_{\rm stat.}\chi_{c1}) mass. However, in this regard, we emphasize
significant discrepancies in the calculation of hyperfine splittings on the
lattice. The leptonic decay constants of and mesons are found to be
MeV and
,
where the first error is statistical, the second a systematic due to chiral
extrapolation and the third error combination of other known systematics. The
- mixing bag parameter, which enters the
transition amplitude, is found to be .Comment: 49 pages, 15 figure
Heavy-Quark Symmetry and the Electromagnetic Decays of Excited Charmed Strange Mesons
Heavy-hadron chiral perturbation theory (HHPT) is applied to the decays
of the even-parity charmed strange mesons, D_{s0}(2317) and D_{s1}(2460).
Heavy-quark spin symmetry predicts the branching fractions for the three
electromagnetic decays of these states to the ground states D_s and D_s^* in
terms of a single parameter. The resulting predictions for two of the branching
fractions are significantly higher than current upper limits from the CLEO
experiment. Leading corrections to the branching ratios from chiral loop
diagrams and spin-symmetry violating operators in the HHPT Lagrangian can
naturally account for this discrepancy. Finally the proposal that the
D_{s0}(2317) (D_{s1}(2460)) is a hadronic bound state of a D (D^*) meson and a
kaon is considered. Leading order predictions for electromagnetic branching
ratios in this molecular scenario are in very poor agreement with existing
data.Comment: 25 pages, 3 figure
Excited B mesons from the lattice
We determine the energies of the excited states of a heavy-light meson
, with a static heavy quark and light quark with mass approximately
that of the strange quark from both quenched lattices and with dynamical
fermions. We are able to explore the energies of orbital excitations up to L=3,
the spin-orbit splitting up to L=2 and the first radial excitation. These mesons will be very narrow if their mass is less than 5775 MeV -- the
threshold. We investigate this in detail and present evidence that the
scalar meson (L=1) will be very narrow and that as many as 6
excited states will have energies close to the threshold and should also
be relatively narrow.Comment: 17 pages, 6 ps figure
Diquark-Antidiquark with open charm in QCD sum rules
Using the QCD sum rule approach we investigate the possible four-quark
structure of the recently observed charmed scalar mesons
(BELLE) and (FOCUS) and also of the very narrow
, firstly observed by BABAR. We use diquak-antidiquark
currents and work to the order of in full QCD, without relying on
expansion. Our results indicate that a four-quark structure is acceptable for
the resonances observed by BELLE and BABAR: and
respectively, but not for the resonances observed by FOCUS:
.Comment: 6 pages, 5 eps figures; Contribution to the 'Workshop on Light-Cone
QCD and Nonperturbative Hadron Physics 2005 (LC2005)', Cairns-Australi
Exact Absorption Probability in the Extremal Six-Dimensional Dyonic String Background
We show that the minimally coupled massless scalar wave equation in the
background of an six-dimensional extremal dyonic string (or D1-D5 brane
intersection) is exactly solvable, in terms of Mathieu functions. Using this
fact, we calculate absorption probabilities for these scalar waves, and present
the explicit results for the first few low energy corrections to the
leading-order expressions. For a specific tuning of the dyonic charges one can
reach a domain where the low energy absorption probability goes to zero with
inverse powers of the logarithm of the energy. This is a dividing domain
between the regime where the low energy absorption probability approaches zero
with positive powers of energy and the regime where the probability is an
oscillatory function of the logarithm of the energy. By the conjectured AdS/CFT
correspondence, these results shed novel light on the strongly coupled
two-dimensional field theory away from its infrared conformally invariant fixed
point (the strongly coupled ``non-critical'' string).Comment: Latex (3 times), 23 page
Waiting for Precise Measurements of K^+->pi^+ nu nu and K_L->pi^0 nu nu
In view of future plans for accurate measurements of the theoretically clean
branching ratios Br(K+ -> pi+ nu nu) and Br(KL -> pi0 nu nu), that should take
place in the next decade, we collect the relevant formulae for quantities of
interest and analyze their theoretical and parametric uncertainties. We point
out that in addition to the angle beta in the unitarity triangle (UT) also the
angle gamma can in principle be determined from these decays with respectable
precision and emphasize in this context the importance of the recent NNLO QCD
calculation of the charm contribution to K+ -> pi+ nu nu and of the improved
estimate of the long distance contribution by means of chiral perturbation
theory. In addition to known expressions we present several new ones that
should allow transparent tests of the Standard Model (SM) and of its
extensions. While our presentation is centered around the SM, we also discuss
models with minimal flavour violation and scenarios with new complex phases in
decay amplitudes and meson mixing. We give a brief review of existing results
within specific extensions of the SM, in particular the Littlest Higgs Model
with T-parity, Z' models, the MSSM and a model with one universal extra
dimension. We derive a new "golden" relation between B and K systems that
involves (beta,gamma) and Br(KL -> pi0 nu nu) and investigate the virtues of
(R_t,beta), (R_b,gamma), (beta,gamma) and (etabar,gamma) strategies for the UT
in the context of K -> pi nu nu decays with the goal of testing the SM and its
extensions.Comment: 56 pages, 18 figures, Section on Long Distance Contributions, 2
Figures and few References added, Uses Rev Mod Phys Style; Includes new
results of NNLO calculation as well as matrix elements, extended and modified
sections on new physic
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