664 research outputs found
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
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
Combinatorial Hopf algebras from renormalization
In this paper we describe the right-sided combinatorial Hopf structure of
three Hopf algebras appearing in the context of renormalization in quantum
field theory: the non-commutative version of the Fa\`a di Bruno Hopf algebra,
the non-commutative version of the charge renormalization Hopf algebra on
planar binary trees for quantum electrodynamics, and the non-commutative
version of the Pinter renormalization Hopf algebra on any bosonic field. We
also describe two general ways to define the associative product in such Hopf
algebras, the first one by recursion, and the second one by grafting and
shuffling some decorated rooted trees.Comment: 16 page
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.
Threshold effects in excited charmed baryon decays
Motivated by recent results on charmed baryons from CLEO and FOCUS, we
reexamine the couplings of the orbitally excited charmed baryons. Due to its
proximity to the [Sigma_c pi] threshold, the strong decays of the
Lambda_c(2593) are sensitive to finite width effects. This distorts the shape
of the invariant mass spectrum in Lambda_{c1}-> Lambda_c pi^+pi^- from a simple
Breit-Wigner resonance, which has implications for the experimental extraction
of the Lambda_c(2593) mass and couplings. We perform a fit to unpublished CLEO
data which gives M(Lambda_c(2593)) - M(Lambda_c) = 305.6 +- 0.3 MeV and h2^2 =
0.24^{+0.23}_{-0.11}, with h2 the Lambda_{c1}-> Sigma_c pi strong coupling in
the chiral Lagrangian. We also comment on the new orbitally excited states
recently observed by CLEO.Comment: 9 pages, 3 figure
Measurement of the Omega_c Lifetime
We present the measurement of the lifetime of the Omega_c we have performed
using three independent data samples from two different decay modes. Using a
Sigma- beam of 340 GeV/c we have obtained clean signals for the Omega_c
decaying into Xi- K- pi+ pi+ and Omega- pi+ pi- pi+, avoiding topological cuts
normally used in charm analysis. The short but measurable lifetime of the
Omega_c is demonstrated by a clear enhancement of the signals at short but
finite decay lengths. Using a continuous maximum likelihood method we
determined the lifetime to be tau(Omega_c) = 55 +13-11(stat) +18-23(syst) fs.
This makes the Omega_c the shortest living weakly decaying particle observed so
far. The short value of the lifetime confirms the predicted pattern of the
charmed baryon lifetimes and demonstrates that the strong interaction plays a
vital role in the lifetimes of charmed hadrons.Comment: 15 pages, including 7 figures; gzipped, uuencoded postscrip
Heavy Meson Decays into Light Resonances
We analyse the Lorentz structures of weak decay matrix elements bewteen meson
states of arbitrary spin. Simplifications arise in the transition amplitudes
for a heavy meson decaying into a light one via a Bethe-Salpeter approach which
incorporates heavy quark symmetry. Phenomenological consequences on several
semileptonic, nonleptonic and FCNC induced decays of heavy flavoured mesons are
derived and discussed.Comment: 20 RevTex pages, Preprint # UTAS-PHYS-94-0
Cabibbo-allowed nonleptonic weak decays of charmed baryons
Cabibbo-allowed nonleptonic weak decays of charmed baryons
\lamc,~\xin,~\xip and into an octet baryon and a pseudoscalar
meson are analyzed. The nonfactorizable contributions are evaluated under pole
approximation, and it turns out that the -wave amplitudes are dominated by
the low-lying \halfm resonances, while -wave ones governed by the
ground-state \halfp poles. The MIT bag model is employed to calculate the
coupling constants, form factors and baryon matrix elements. Our conclusions
are: (i) waves are no longer dominated by commutator terms; the
current-algebra method is certainly not applicable to parity-violating
amplitudes, (ii) nonfactorizable exchange effects are generally important;
they can be comparable to and somtimes even dominate over factorizable
contributions, depending on the decay modes under consideration, (iii)
large- approximation for factorizable amplitudes also works in the heavy
baryon sector and it accounts for the color nonsuppression of \lamc\ri
p\bar{K}^0 relative to \lamc\ri\Lambda\pi^+, (iv) a measurement of the decay
rate and the sign of the asymmetry parameter of certain proposed decay
modes will help discern various models; especially the sign of in
\lamc\ri\Sigma\pi decays can be used to unambiguously differentiate recent
theoretical schemes from current algebra, and (v) waves are the dominant
contributions to the decays \lamc\ri\Xi^0 K^+ and \xin\ri\Sigma^+ K^-, but
they are subject to a large cancellation; this renders present theoretical
predictions on these two channels unreliable.Comment: PHYZZX, 31 pages, 3 tables, IP-ASTP-10-93, ITP-SB-93-2
A New Interpretation of the Observed Heavy Baryons
I suggest that the conventional assignment of quantum numbers to the observed
charm and bottom baryons is not correct, as these assignments imply large
violation of the heavy spin-flavor and light symmetries. I propose an
alternative interpretation of the observed states, in which the symmetries are
preserved. If these novel assignments are right, there is a new state with mass
approximately 2380~MeV which decays to , and another with
mass approximately 5760~MeV which decays to . Although such
states have not been seen, neither are they excluded by current analyses.Comment: REVTeX, 7 pages. This is the final version to appear in Physical
Review Letters. Two typos in Eq. (1) have been fixed and several points
elsewhere have been clarified; also, there is now a brief discussion of the
relationship of this proposal to the nonrelativistic constituent quark mode
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