5,215 research outputs found
Nonleptonic Weak Decays of B to D_s and D mesons
Branching ratios and polarization amplitudes for B decaying to all allowed
pseudoscalar, vector, axial-vector, scalar and tensor combinations of D_s and D
mesons are calculated in the Isgur Scora Grinstein Wise (ISGW) quark model
after assuming factorization. We find good agreement with other models in the
literature and the limited experimental data and make predictions for as yet
unseen decay modes. Lattice QCD results in this area are very limited. We make
phenomenological observations on decays in to D_s(2317) and D_s(2460) and
propose tests for determining the status and mixings of the axial mesons. We
use the same approach to calculate branching ratios and polarization fraction
for decays in to two D type mesons.Comment: 21 pages, 9 figures. v3: updated to reflect changes in published
paper, conclusions unchanged (see source file for details). Added comments on
factorization. v2: experimental data updated, references added, tables of
results added, more on axial D_s mixing, added section on D D decay modes and
typos correcte
Simply Modeling Meson HQET
A simple relativistic model of heavy-quark-light-quark mesons is proposed. In
an expansion in inverse powers of the heavy quark mass we find that all zeroth
and first order heavy quark symmetry relations are satisfied. The main results
are: - the difference between the meson mass and the heavy quark mass plays a
significant role even at zeroth order; - the slope of the Isgur-Wise function
at the zero recoil point is typically less than ; - the first order
correction to the pseudoscalar decay constant is large and negative; - the four
universal functions describing the first order corrections to the semileptonic
decay form factors are small; - these latter corrections are quite insensitive
to the choice of model parameters, and in particular to the effects of
hyperfine mass splitting.Comment: 17 pages, LaTeX, 3 LaTeX figures in separate file, UTPT-92-16. This
is the version published long ago but not previously archive
Note on Tests of the Factorization Hypothesis and the Determination of Meson Decay Constants
We discuss various tests of the factorization hypothesis making use of the
close relationship between semi-leptonic and factorized nonleptonic decay
amplitudes. It is pointed out that factorization leads to truely
model-independent predictions for the ratio of nonleptonic to semi-leptonic
decay rates, if in the nonleptonic decay a spin one meson of arbitrary mass or
a pion take the place of the lepton pair. Where the decay constants of those
mesons are known, these predictions represent ideal tests of the factorization
hypothesis. In other cases they may be used to extract the decay constants.
Currently available data on the decays are shown to be in excellent agreement with
the factorization results. A weighted average of the four independent values
for the QCD coefficient extracted from the data gives
suggesting that it may be equal to the Wilson coefficient evaluated
at the scale .Comment: (9 pages, ReVTeX, no figures), HD-THEP-92-3
Infrared singularities of scattering amplitudes in perturbative QCD
An exact formula is derived for the infrared singularities of dimensionally
regularized scattering amplitudes in massless QCD with an arbitrary number of
legs, valid at any number of loops. It is based on the conjecture that the
anomalous-dimension matrix of n-jet operators in soft-collinear effective
theory contains only a single non-trivial color structure, whose coefficient is
the cusp anomalous dimension of Wilson loops with light-like segments. Its
color-diagonal part is characterized by two anomalous dimensions, which are
extracted to three-loop order from known perturbative results for the quark and
gluon form factors. This allows us to predict the three-loop coefficients of
all 1/epsilon^k poles for an arbitrary n-parton scattering amplitudes,
generalizing existing two-loop results.Comment: 4 pages; v2: typo in eq. (12) fixed, references updated; v3:
additional term in (12
Determinations of |V_ub| and |V_cb| from measurements of B -> X_u,c\ell\nu differential decay rates
Methods are described in the framework of light-cone expansion which allow
one to determine the Cabibbo-Kobayashi-Maskawa matrix elements |V_ub| and
|V_cb| from measurements of the differential decay rates as a function of the
scaling variables in the inclusive semileptonic decays of B mesons. By these
model-independent methods the dominant hadronic uncertainties can be avoided
and the B -> X_u\ell\nu decay can be very efficiently differentiated from the B
-> X_c\ell\nu decay, which may lead to precise determinations of |V_ub| and
|V_cb|.Comment: 11 pages, 2 figures, version as published in Mod. Phys. Lett. A, more
discussion, references added, title chang
The emission of energetic electrons from the complex streamer corona adjacent to leader stepping
We here propose a model to capture the complexity of the streamer corona
adjacent to leader stepping and relate it to the production of energetic
electrons serving as a source of X-rays and -rays, manifesting in
terrestrial gamma-ray flashes (TGFs). During its stepping, the leader tip is
accompanied by a corona consisting of multitudinous streamers perturbing the
air in its vicinity and leaving residual charge behind. We explore the relative
importance of air perturbations and preionization on the production of
energetic run-away electrons by 2.5D cylindrical Monte Carlo particle
simulations of streamers in ambient fields of 16 kV cm and 50 kV
cm at ground pressure. We explore preionization levels between
m and m, channel widths between 0.5 and 1.5 times the
original streamer widths and air perturbation levels between 0\% and 50\% of
ambient air. We observe that streamers in preionized and perturbed air
accelerate more efficiently than in non-ionized and uniform air with air
perturbation dominating the streamer acceleration. We find that in unperturbed
air preionization levels of m are sufficient to explain
run-away electron rates measured in conjunction with terrestrial gamma-ray
flashes. In perturbed air, the production rate of runaway electrons varies from
s to s with maximum electron energies from
some hundreds of eV up to some hundreds of keV in fields above and below the
breakdown strength. In the presented simulations the number of runaway
electrons matches with the number of energetic electrons measured in alignment
with the observations of terrestrial gamma-ray flashes. Conclusively, the
complexity of the streamer zone ahead of leader tips allows explaining the
emission of energetic electrons and photons from streamer discharges.Comment: 29 pages, 11 figures, 2 table
Decays of bottom mesons emitting tensor meson in final state using ISGW II model
In this paper, we investigate phenomenologically two-body weak decays of the
bottom mesons emitting pseudoscalar/vector meson and a tensor meson. Form
factors are obtained using the improved ISGW II model. Consequently, branching
ratios for the CKM-favored and CKM-suppressed decays are calculated.Comment: 32 pages, to be published in Phys. Rev.
Slope of the Isgur-Wise function in the heavy mass limit of quark models \`a la Bakamjian-Thomas
The slope of the Isgur-Wise function for ground state mesons is evaluated for
the heavy mass limit of quark models \`a la Bakamjian-Thomas, which has been
previously discussed by us in general terms. A full calculation in various
spectroscopic models with relativistic kinetic energy gives a rather stable
result , much lower than previous estimates. Attention is
paid to a careful comparison of this result with the ones of QCD fundamental
methods (lattice QCD, QCD sum rules) and with experimental data.Comment: 15 pages, Latex, AMS-LaTe
Second Order Power Corrections in the Heavy Quark Effective Theory I. Formalism and Meson Form Factors
In the heavy quark effective theory, hadronic matrix elements of currents
between two hadrons containing a heavy quark are expanded in inverse powers of
the heavy quark masses, with coefficients that are functions of the kinematic
variable . For the ground state pseudoscalar and vector mesons, this
expansion is constructed at order . A minimal set of universal form
factors is defined in terms of matrix elements of higher dimension operators in
the effective theory. The zero recoil normalization conditions following from
vector current conservation are derived. Several phenomenological applications
of the general results are discussed in detail. It is argued that at zero
recoil the semileptonic decay rates for and receive only small second order corrections, which are unlikely
to exceed the level of a few percent. This supports the usefulness of the heavy
quark expansion for a reliable determination of .Comment: (34 pages, REVTEX, two postscript figures available upon request),
SLAC-PUB-589
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