12 research outputs found
Quark model predictions for the electron energy spectrum in seileptonic D and B decays
The constituent quark model is used to predict the electron
energy spectrum in semileptonic D and B meson decays. Particular attention is paid to the endpoint region of the electron spectrum in B decays since this is crucial to a determination of the b --> u weak mixing angle
Quark model predictions for the electron energy spectrum in seileptonic D and B decays
The constituent quark model is used to predict the electron
energy spectrum in semileptonic D and B meson decays. Particular attention is paid to the endpoint region of the electron spectrum in B decays since this is crucial to a determination of the b --> u weak mixing angle
Semileptonic B and Lambda_b Decays and Local Duality in QCD
The inclusive and exclusive semileptonic decay distributions for b -> c decay
are computed in the Shifman-Voloshin limit. The inclusive decay distributions
(computed using an operator product expansion) depend on quark masses, and the
exclusive decay distributions depend on hadron masses. Nevertheless, we show
explicitly how the first two terms in the 1/m expansion match between the
inclusive and exclusive decays. Agreement between the inclusive and exclusive
decay rates requires a minimum smearing region of size Lambda_QCD before local
duality holds in QCD. The alpha_s corrections to the inclusive and exclusive
decay rates are also shown to agree to order (log m)/m^2. The alpha_s/m^2
corrections are used to obtain the alpha_s correction to Bjorken's inequality
on the slope of the Isgur-Wise function.Comment: 22 pages, 3 eps figures, uses revtex (Revision: a discussion of
radiative corrections to the bound K>0 of Section 7.B has been added; some
typos, including labels in fig 2
Perturbative corrections to zero recoil inclusive decay sum rules
Comparing the result of inserting a complete set of physical states in a time
ordered product of decay currents with the operator product expansion gives
a class of zero recoil sum rules. They sum over physical states with excitation
energies less than , where is much greater than the QCD scale
and much less than the heavy charm and bottom quark masses. These sum rules
have been used to derive an upper bound on the zero recoil limit of the form-factor, and on the matrix element of the kinetic energy operator
between meson states. Perturbative corrections to the sum rules of order
have previously been computed. We
calculate the corrections of order and keeping all orders in , and show that these
perturbative QCD corrections suppressed by powers of
significantly weaken the upper bound on the zero recoil form-factor,
and also on the kinetic energy operator's matrix element.Comment: 13 pages revtex, four figures included; minor change
Semileptonic B and D decays in the quark model
We predict the matrix elements and resulting electron spectra for semileptonic meson decays using the quark potential model. Particular attention is paid to the high-energy electron end-point region in B decay since it is crucial to a determination of the b→u weak mixing angle. It is argued that in this region the usual inclusive ("quark decay") calculations are unjustified and must be replaced by explicit sums over decays of the original meson into low-mass exclusive hadronic final states
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The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic