276 research outputs found
QCD Sum Rules Calculation of Heavy Semileptonic Decay
We set up sum rules for heavy lambda decays in a full QCD calculation which
in the heavy quark mass limit incorporates the symmetries of heavy quark
effective theory. For the semileptonic \La_c decay we obtain a reasonable
agreement with experiment. For the \La_b semileptonic decay we find at the
zero recoil point a violation of the heavy quark symmetry of about 20%.Comment: Revised version. Title changed. 11 pages (RevTex), 4 PS figure
couplings and D^*\rar D\pi(\gamma) -decays within a -expansion in QCD
To leading order in , we evaluate the leading and non-leading
corrections to the and couplings using QCD
spectral moment sum rules in the full theory. We find that, for large and
contrary to the heavy-to-light B\rar \pi(\rho) l\bar \nu form factors, which
are dominated by the light quark vacuum condensate, these couplings are
governed by the perturbative graph, like other heavy-to-heavy
transitions. We also find that for the B^{*}\rar B\gamma, the
correction is mainly due to the perturbative and light quark condensate
contributions originating from the graphs involving the heavy quark part of the
electromagnetic current, which are essential for explaining the large charge
dependence in the observed D^{*-}\rar D^-\gamma and D^{*0}\rar D^0\gamma
decays. Our numerical predictions {\it without any free parameters} for
the -meson are: , \Gamma_{B^{*-}\rar
B^-\gamma}\simeq (0.10\pm 0.03) keV and the large charge dependence of the
ratio: {\Gamma_{B^{*-}\rar B^- \gamma}}/ {\Gamma_{B^{*0}\rar B^0
\gamma}}\simeq 2.5~. For the -meson, we find: \Gamma_{D^{*-}\rar
D^0\pi^-}\simeq 1.54\Gamma_{D^{*0}\rar D^0\pi^0} \simeq (8\pm 5) keV,
\Gamma_{D^{*-}\rar D^-\gamma}\simeq (0.09^{+0.40}_{-0.07} ) keV and
\Gamma_{D^{*0}\rar D^0\gamma}\simeq (3.7\pm 1.2) keV, where the branching
ratios agree within the errors with the present data, while the total widths
\Gamma_{D^{*0}\rar all} \simeq (11\pm 4) keV and \Gamma_{D^{*-}\rar
all}\simeq (12\pm 7) keV are much smaller than the present experimental upper
limits.Comment: published version to appear in Phys. Lett. B (minor modifications
compared with the previous version
Magnetic string contribution to hadron dynamics in QCD
Dynamics of a light quark in the field of static source (heavy-light meson)
is studied using the nonlinear Dirac equation, derived recently. Special
attention is paid to the contribution of magnetic correlators and it is found
that it yields a significant increase of string tension at intermediate
distances. The spectrum of heavy-light mesons is computed with account of this
contribution and compared to experimental and lattice data.Comment: 10 pages Revte
Rare Decays of \Lambda_b->\Lambda + \gamma and \Lambda_b ->\Lambda + l^{+} l^{-} in the Light-cone Sum Rules
Within the Standard Model, we investigate the weak decays of and with the light-cone
sum rules approach. The higher twist distribution amplitudes of
baryon to the leading conformal spin are included in the sum rules for
transition form factors. Our results indicate that the higher twist
distribution amplitudes almost have no influences on the transition form
factors retaining the heavy quark spin symmetry, while such corrections can
result in significant impacts on the form factors breaking the heavy quark spin
symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of
baryon are also employed in the sum rules for a comparison, which can
give rise to the form factors approximately 5 times larger than that in terms
of conformal expansion. Utilizing the form factors calculated in LCSR, we then
perform a careful study on the decay rate, polarization asymmetry and
forward-backward asymmetry, with respect to the decays of , .Comment: 38 pages, 15 figures, some typos are corrected and more references
are adde
The transition form factors for semi-leptonic weak decays of in QCD sum rules
Within the Standard Model, we investigate the semi-leptonic weak decays of
. The various form factors of transiting to a single charmed
meson () are studied in the framework of the QCD sum rules.
These form factors fully determine the rates of the weak semi-leptonic decays
of and provide valuable information about the non-perturbative QCD
effects. Our results indicate that the decay rate of the semi-leptonic weak
decay mode is at order of .Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.
Force-Extension Relations for Polymers with Sliding Links
Topological entanglements in polymers are mimicked by sliding rings
(slip-links) which enforce pair contacts between monomers. We study the
force-extension curve for linear polymers in which slip-links create additional
loops of variable size. For a single loop in a phantom chain, we obtain exact
expressions for the average end-to-end separation: The linear response to a
small force is related to the properties of the unstressed chain, while for a
large force the polymer backbone can be treated as a sequence of Pincus--de
Gennes blobs, the constraint effecting only a single blob. Generalizing this
picture, scaling arguments are used to include self-avoiding effects.Comment: 4 pages, 5 figures; accepted to Phys. Rev. E (Brief Report
Four-fermion heavy quark operators and light current amplitudes in heavy flavor hadrons
We introduce and study the properties of the "color-straight" four-quark
operators containing heavy and light quark fields. They are of the form (\bar
b\Gamma_b b)(\bar q\Gamma_q q) where both brackets are color singlets. Their
expectation values include the bulk of the nonfactorizable contributions to the
nonleptonic decay widths of heavy hadrons. The expectation values of the
color-straight operators in the heavy hadrons are related to the momentum
integrals of the elastic light-quark formfactors of the respective heavy
hadron. We calculate the asymptotic behavior of the light-current formfactors
of heavy hadrons and show that the actual decrease is 1/(q^2)^3/2 rather than
1/q^4. The two-loop hybrid anomalous dimensions of the four-quark operators and
their mixing (absent in the first loop) are obtained. Using plausible models
for the elastic formfactors, we estimate the expectation values of the
color-straight operators in the heavy mesons and baryons. Improved estimates
will be possible in the future with new data on the radiative decays of heavy
hadrons. We give the Wilson coefficients of the four-fermion operators in the
1/m_b expansion of the inclusive widths and discuss the numerical predictions.
Estimates of the nonfactorizable expectation values are given.Comment: 51 pages. The case of flavor-singlet operators is added for the
two-loop anomalous dimension
decays into and mesons
We consider the nonleptonic and semileptonic decays of -mesons into
and mesons. QCD sum rules are used to calculate the form
factors associated with these decays, and the correspondig decay rates. On the
basis of data on , which goes dominantly via the
transition , we conclude that there is space for a
sizeable light quark component on .Comment: 14 pages, RevTeX4 including 5 figures in ps file
A Bayesian analysis of pentaquark signals from CLAS data
We examine the results of two measurements by the CLAS collaboration, one of
which claimed evidence for a pentaquark, whilst the other found no
such evidence. The unique feature of these two experiments was that they were
performed with the same experimental setup. Using a Bayesian analysis we find
that the results of the two experiments are in fact compatible with each other,
but that the first measurement did not contain sufficient information to
determine unambiguously the existence of a . Further, we suggest a
means by which the existence of a new candidate particle can be tested in a
rigorous manner.Comment: 5 pages, 3 figure
Electron Scattering From High-Momentum Neutrons in Deuterium
We report results from an experiment measuring the semi-inclusive reaction
where the proton is moving at a large angle relative to the
momentum transfer. If we assume that the proton was a spectator to the reaction
taking place on the neutron in deuterium, the initial state of that neutron can
be inferred. This method, known as spectator tagging, can be used to study
electron scattering from high-momentum (off-shell) neutrons in deuterium. The
data were taken with a 5.765 GeV electron beam on a deuterium target in
Jefferson Laboratory's Hall B, using the CLAS detector. A reduced cross section
was extracted for different values of final-state missing mass ,
backward proton momentum and momentum transfer . The data
are compared to a simple PWIA spectator model. A strong enhancement in the data
observed at transverse kinematics is not reproduced by the PWIA model. This
enhancement can likely be associated with the contribution of final state
interactions (FSI) that were not incorporated into the model. A ``bound neutron
structure function'' was extracted as a function of and
the scaling variable at extreme backward kinematics, where effects of
FSI appear to be smaller. For MeV/c, where the neutron is far
off-shell, the model overestimates the value of in the region of
between 0.25 and 0.6. A modification of the bound neutron structure
function is one of possible effects that can cause the observed deviation.Comment: 33 pages RevTeX, 9 figures, to be submitted to Phys. Rev. C. Fixed 1
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