782 research outputs found
Charm lifetime
A review of the charmed meson and baryon lifetimes is presented. Our
knowledge of charmed particle lifetimes has greatly improved over the past two
years, a crucial r\^ole having been played by the E687 experiment at Fermilab,
which has almost quadrupled the samples of mesons. The lifetime ratios
and are now known with an
accuracy of 1.7\% and 3.7\% respectively. In the baryon sector the statistics
is still limited, but the experimental results on , and
exhibit a clear pattern of lifetime hierarchy, as expected from
simple theoretical arguments. The first measurement of from
E687 is also presented to complete the charmed baryon lifetime picture. The
more accurate experimental scenario can provide information on non-perturbative
QCD effects and the hadronic matrix elements.Comment: 10 pages, latex, 3 figures. Talk presented at the 6th. International
Symposium on Heavy Flavour Physics (Pisa, June 1995
Effect of CH addition on excess electron mobility in liquid Kr
The excess electrons mobility has been measured recently in liquid
mixtures of Kr and CH as a function of the electric field up to and of the CH concentration up to at
temperatures fairly close to the normal boiling point of Kr
(folegani). We present here new data which extend the
previous set in the region of low electric field. The experimental results are
interpreted in terms of a kinetic model previously proposed to explain the
concentration dependent behavior of in liquid Ar--Kr and Ar--Xe mixtures.
The main result is that CH is more effective in enhancing
energy--transfer rather than momentum--transfer in comparison with mixtures of
liquified noble gases. The field dependence of is quite complicate. In
particular, at intermediate values of the field, there appears to be a
crossover between two different electric--field dependent behaviors of
The electric field strength at crossover is well correlated with the
concentration of CH This fact suggests that different excitations of the
molecular solute might be involved in the momentum-- and energy--transfer
processes for different values of the mean electron energy.Comment: 17, pages,7 figures, RevTeX4, submitted to J.Chem.Phy
Scalar meson properties from D-meson decays
Decay amplitudes of D(D_s)->f0(980)X, X=pi, K, are compared to experimental
branching ratios with the aim of singling out the poorly known D->f0(980)
transition form factor in these amplitudes. Since the other elements of the
amplitudes are either calculable in an effective QCD theory using operator
product expansion or are known from experiment (e.g. the pion and kaon decay
constants), we can take advantage of these reactions to constrain the
transition form factors obtained in relativistic quark models. In these models,
the f0(980) wavefunction requires an unknown size parameter for both its
non-strange ubar u(dbar d) and strange sbar s components, which we fit to the
D(D_s) decay data.Comment: Talk given at the Few Body 18 conference in Santos, Brazil. 4 pages,
to be published in Nuclear Physics
Charmed Baryons with
The width of a recently discovered excited charmed-strange baryon, a
candidate for a state with spin 3/2, is calculated. In the absence of
configuration mixing between the ground-state (spin-1/2) charmed-strange baryon
and the spin-1/2 state lying about 95 MeV above it,
one finds and , where the tilde denotes the partial
width with kinematic factors removed. Assuming a kinematic factor for P-wave
decay of , one predicts MeV, while the channel is closed. Some
suggestions are given for detecting the , the spin-3/2 charmed
nonstrange baryon, and the , the spin-3/2 charmed doubly-strange
baryon.Comment: 11 pages, latex, 2 uuencoded figures sent separatel
Electron drift velocity measurements in liquid kryptonâmethane mixtures
Abstract Electron drift velocities have been measured in liquid krypton, pure and mixed with methane at different concentrations (1â10% in volume) versus electric field strength, and a possible effect of methane on electron lifetime has been investigated. While no effect on lifetime could be detected, since lifetimes were in all cases longer than what measurable, a very large increase in drift velocity (up to a factor 6) has been measured
One-pion transitions between heavy baryons in the constituent quark model
Single pion transitions of S wave to S wave, P wave to S wave and P wave to P
wave heavy baryons are analyzed in the framework of the Heavy Quark Symmetry
limit (HQS). We use a constituent quark model picture for the light diquark
system with an underlying SU(2N_{f}) X O(3) symmetry to reduce the number of
the HQS coupling factors required to describe these transitions. We also use
the quantum theory of angular momentum to rewrite the one-pion transitions
constituent quark model results in a more general form using the 6j- and
9j-symbols. We finally estimate the decay rates of some single pion transitions
between charm baryon states.Comment: Latex, 33 pages including 2 figures (Postscript). Some typos are
corrected with minor changes. Two references were added to the final version
which will appear in Phy. Rev.
Decay
Motivated by the experimental measurement of the decay rate, , and
the longitudinal polarization, , in the Cabibbo favored decay , we have studied theoretical prediction within the context of
factorization approximation invoking several form factors models. We were able
to obtain agreement with experiment for both and by using
experimentally measured values of the form factors ,
and in the semi-leptonic decay . We have also included in our calculation the effect of the
final state interaction () by working with the partial waves amplitudes
, and . Numerical calculation shows that the decay amplitude is
dominated by wave, and that the polarization is sensitive to the
interference between and waves. The range of the phase difference
accommodated by experimental error in
is large.Comment: 7 pages, LaTe
Nonresonant Three-body Decays of D and B Mesons
Nonresonant three-body decays of D and B mesons are studied. It is pointed
out that if heavy meson chiral perturbation theory (HMChPT) is applied to the
heavy-light strong and weak vertices and assumed to be valid over the whole
kinematic region, then the predicted decay rates for nonresonant charmless
3-body B decays will be too large and especially B^- --> pi^- K^+ K^- greatly
exceeds the current experimental limit. This can be understood as chiral
symmetry has been applied there twice beyond its region of validity. If HMChPT
is applied only to the strong vertex and the weak transition is accounted for
by the form factors, the dominant B^* pole contribution to the tree-dominated
direct three-body B decays will become small and the branching ratio will be of
order 10^{-6}. The decay modes B^- --> (K^- h^+ h^-)_{NR} and bar{B}^0 -->
(bar{K}^0 h^+h^-)_{NR} for h = pi, K are penguin dominated. We apply HMChPT in
two different cases to study the direct 3-body D decays and compare the results
with experiment. Theoretical uncertainties are discussed.Comment: 24 pages, 2 figures. New experimental results of direct 3-body D
decays as Reported at ICHEP2002 are included. To appear in Phys. Re
Strong Decays of Strange Charmed P-Wave Mesons
Goldstone boson decays of P-wave mesons are studied within the
framework of Heavy Hadron Chiral Perturbation Theory. We first analyze the
simplest single kaon decays of these strange charmed mesons. We derive a model
independent prediction for the width of and use experimental
information on to constrain the S-wave contribution to decay.
Single and double pion decay modes are then discussed and shown to be
significantly restricted by isospin conservation. We conclude that the pion
channels may offer the best hope for detecting one strange member of an
otherwise invisible P-wave flavor multiplet.Comment: 16 pages, 2 updated figures not included but available upon request,
CALT-68-1902. (Revised estimates for error on width and for isospin
violating neutral pion decay of .
- âŠ