28,195 research outputs found
B->gamma e nu Transitions from QCD Sum Rules
B->gamma e nu transitions have recently been studied in the framework of QCD
factorization. The attractiveness of this channel for such an analysis lies in
the fact that, at least in the heavy quark limit, the only hadron involved is
the B meson itself, so one expects a very simple description of the form factor
in terms of a convolution of the B meson distribution amplitude with a
perturbative kernel. This description, however, does not include contributions
suppressed by powers of the b quark mass. In this letter, we calculate
corrections to the factorized expression which are induced by the ``soft''
hadronic component of the photon. We demonstrate that the power-suppression of
these terms is numerically not effective for physical values of the quark
mass and that they increase the form factor by about 30% at zero momentum
transfer. We also derive a sum rule for lambda_B, the first negative moment of
the B meson distribution amplitude, and find lambda_B = 0.6 GeV (to leading
order in QCD).Comment: 13 pages, 5 figure
A DAQ System for Linear Collider TPC Prototypes based on the ALEPH TPC Electronics
Within the international studies of a high energy linear electron positron
collider, several groups are developing and testing prototypes for a Linear
Collider TPC. This detector is planned to be used as a central part in the
tracking system of a detector at such a machine. In this note we describe a DAQ
system, which has been developed for the use in tests of TPC prototypes. It is
based on electronics used at the ALEPH experiment at CERN.Comment: 15 pages, 4 figure
Heavy to Light Meson Exclusive Semileptonic Decays in Effective Field Theory of Heavy Quark
We present a general study on exclusive semileptonic decays of heavy (B, D,
B_s) to light (pi, rho, K, K^*) mesons in the framework of effective field
theory of heavy quark. Transition matrix elements of these decays can be
systematically characterized by a set of wave functions which are independent
of the heavy quark mass except for the implicit scale dependence. Form factors
for all these decays are calculated consistently within the effective theory
framework using the light cone sum rule method at the leading order of 1/m_Q
expansion. The branching ratios of these decays are evaluated, and the heavy
and light flavor symmetry breaking effects are investigated. We also give
comparison of our results and the predictions from other approaches, among
which are the relations proposed recently in the framework of large energy
effective theory.Comment: 18 pages, ReVtex, 5 figures, added references and comparison of
results, and corrected signs in some formula
Light-cone sum rules for form factors revisited
We reconsider and update the QCD light-cone sum rules for form
factors. The gluon radiative corrections to the twist-2 and twist-3 terms in
the correlation functions are calculated. The -quark mass is
employed, instead of the one-loop pole mass used in the previous analyses. The
light-cone sum rule for is fitted to the measured
-distribution in , fixing the input parameters with the
largest uncertainty: the Gegenbauer moments of the pion distribution amplitude.
For the vector form factor at zero momentum transfer we predict
. Combining it with the value of the
product extracted from experiment, we obtain
. In addition, the scalar
and penguin form factors and are
calculated.Comment: 33 pages, 7 figures, one figure and a few comments added, version to
appear in JHE
Analysis of B-> \phi K Decays in QCD Factorization
We analyze the decay within the framework of QCD-improved
factorization. We found that although the twist-3 kaon distribution amplitude
dominates the spectator interactions, it will suppress the decay rates
slightly. The weak annihilation diagrams induced by penguin
operators, which are formally power-suppressed by order , are
chirally and logarithmically enhanced. Therefore, these annihilation
contributions are not subject to helicity suppression and can be sizable. The
predicted branching ratio of is in
the absence of annihilation contributions and it becomes
when annihilation effects are taken into
account. The prediction is consistent with CLEO and BaBar data but smaller than
the BELLE result.Comment: 13 pages, 3 figures. A major change for the presentation of
branching-ratio predictions. Experimental data are update
The Form Factor in The Whole Kinematically Accessible Range
A systematic analysis is presented of the form factor in the whole range of momentum transfer , which would be useful to
analyzing the future data on decays and extracting .
With a modified QCD light cone sum rule (LCSR) approach, in which the
contributions cancel out from the twist 3 wavefunctions of meson, we
investigate in detail the behavior of at small and intermediate
and the nonperturbative quantity
is the decay constant of meson and
the strong coupling), whose numerical
result is used to study dependence of at large in
the single pole approximation. Based on these findings, a form factor model
from the best fit is formulated, which applies to the calculation on
in the whole kinematically accessible range. Also, a comparison is made with
the standard LCSR predictions.Comment: 11 pages, Latex, 1 eps figure, Final version to appear in Phys.Rev.
Lattice deformations at martensite-martensite interfaces in Ni-Al
The atomic configurations at macrotwin interfaces between microtwinned martensite plates in material are investigated using high resolution transmission electron microscopy (HRTEM). The observed structures are interpreted in view of possible formation mechanisms of these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular \{110\} austenite planes, enclose a final angle larger or smaller than , measured over the boundary. Two different configurations, one with crossing microtwins and the other with ending microtwins producing a step configuration are described. The latter is related with the existence of microtwin sequences with changing variant widths. Although both features appear irrespective of the material’s preparation technique, rapid solidification seems to prefer the step configuration. Depending on the actual case, tapering, bending and tip splitting of the small microtwin variants is observed. Sever lattice deformations and reorientations occur in a region of 5 – 10 nm around the interface while sequences of single plane ledges gradually bending the microtwins are found up to 50 nm away form the interface. These structures and deformations are interpreted in view of the need to accommodate any remaining stresses
Incompatible sets of gradients and metastability
We give a mathematical analysis of a concept of metastability induced by
incompatibility. The physical setting is a single parent phase, just about to
undergo transformation to a product phase of lower energy density. Under
certain conditions of incompatibility of the energy wells of this energy
density, we show that the parent phase is metastable in a strong sense, namely
it is a local minimizer of the free energy in an neighbourhood of its
deformation. The reason behind this result is that, due to the incompatibility
of the energy wells, a small nucleus of the product phase is necessarily
accompanied by a stressed transition layer whose energetic cost exceeds the
energy lowering capacity of the nucleus. We define and characterize
incompatible sets of matrices, in terms of which the transition layer estimate
at the heart of the proof of metastability is expressed. Finally we discuss
connections with experiment and place this concept of metastability in the
wider context of recent theoretical and experimental research on metastability
and hysteresis.Comment: Archive for Rational Mechanics and Analysis, to appea
decays in the pQCD approach
We calculate the CP averaged branching ratios and CP-violating asymmetries
for and
decays in the perturbative QCD (pQCD) approach here. The pQCD predictions for
the CP-averaged branching ratios are Br(B_s^0 \to \eta \eta) = \left
(14.2^{+18.0}_{-7.5}) \times 10^{-6}, Br(B_s^0 \to \eta \eta^\prime)= \left
(12.4 ^{+18.2}_{-7.0}) \times 10^{-6}, and Br(B_s^0 \to \eta^{\prime}
\eta^{\prime}) = \left (9.2^{+15.3}_{-4.9}) \times 10^{-6}, which agree well
with those obtained by employing the QCD factorization approach and also be
consistent with available experimental upper limits. The gluonic contributions
are small in size: less than 7% for and
decays, and around 18% for decay. The CP-violating
asymmetries for three decays are very small: less than 3% in magnitude.Comment: 11 pages, 1 ps figure, Revte
The Semileptonic Decays and from QCD Sum Rules
We investigate the semileptonic decays of B and D mesons into and
mesons, respectively, by means of QCD sum rules. We find that for the
vector formfactors involved the pole dominance hypothesis is valid to good
accuracy with pole masses in the expected range. Pole dominance, however, does
not apply to the axial formfactors which results in specific predictions for
the predominant polarization of the meson and the shape of the lepton
spectrum. For the total decay rates we find , , and .Comment: 23 pages, 12 figures included as uu-encoded file, needs REVTEX,
TUM--T31--39/9
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