362 research outputs found
Charmonium dynamics in nucleus-nucleus collisions at SPS and FAIR energies
Charmonium production and suppression in In+In and Pb+Pb reactions at SPS
energies is investigated with the HSD transport approach within the 'hadronic
comover model' as well as the 'QGP threshold scenario'. The results of the
transport calculations for J/Psi suppression and the Psi prime to J/Psi ratio
are compared with the recent data of the NA50 and NA60 Collaborations. We find
that the comover absorption model - with a single parameter |M_0|^2 for the
matrix element squared for charmonium-meson dissociation - performs best with
respect to all data sets. The 'threshold scenario' - within different
assumptions for the melting energy densities - yields a reasonable suppression
for J/Psi but fails in reproducing the Psi prime to J/Psi ratio for Pb+Pb at
158 A GeV. Predictions for Au+Au reactions are presented for a bombarding
energy of 25 A GeV in the different scenarios which will allow for a clear
distinction between the models from the experimental side at the future FAIR
facility.Comment: 22 pages, 10 figures. v2: comments added according to referee
suggestions; references updated; Nucl. Phys. A, in pres
Spin Dependent Fragmentation Functions for Heavy Flavor Baryons and Single Heavy Hyperon Polarization
Spin dependent fragmentation functions for heavy flavor quarks to fragment
into heavy baryons are calculated in a quark-diquark model. The production of
intermediate spin 1/2 and 3/2 excited states is explicity included.
, and production rate and polarization at LEP energies are
calculated and, where possible, compared with experiment. A different approach,
also relying on a heavy quark-diquark model, is proposed for the small momentum
transfer inclusive production of polarized heavy flavor hyperons. The predicted
polarization is roughly in agreement with experiment.Comment: LaTeX2e 11 pages with 4 PostScript figures. To be published in
Proceedings of the International Workshop ``Symmetries and spin'',
Praha-SPIN-200
Radiative Leptonic Decays of Heavy Mesons
We compute the photon spectrum and the rate for the decays These photonic modes constitute a potentially large background
for the purely leptonic decays which are used to extract the heavy meson decay
constants. While the rate for D\to l\n\g is small, the radiative decay in the
meson case could be of comparable magnitude or even larger than B\to\m\n.
This would affect the determination of if the channel cannot be
identified. We obtain theoretical estimates for the photonic rates and disscuss
their possible experimental implications.Comment: 12 pages, RevTex, 3 uuencoded figures include
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
Properties of the Lambda(1520) Resonance from High-Precision Electroproduction Data
High-resolution spectrometer measurements of the reaction H(e,e'K+)X at small
Q2 are used to extract the mass and width of the Lambda(1520). We investigate
the influence of various assumptions used in the extraction. The width appears
to be more sensitive to the assumptions than the mass. To reach a width
uncertainty about 1 MeV or better, one needs to know the structure of the
non-resonant background. Based on the new Jefferson Lab Hall A data, our final
values for the Breit-Wigner parameters are M = 1520.4 +- 0.6 (stat) +- 1.5
(syst) MeV, Gamma = 18.6 +- 1.9 (stat) +- 1 (syst) MeV. For the first time, we
also estimate the pole position for this resonance and find that both the pole
mass and width seem to be smaller than the Breit-Wigner values.Comment: 7 pages, 3 figures; corresponds to the published versio
Relating parton model and color dipole formulation of heavy quark hadroproduction
At high center of mass energies, hadroproduction of heavy quarks can be
expressed in terms of the same color dipole cross section as low Bjorken-x deep
inelastic scattering. We show analytically that at leading order, the dipole
formulation is equivalent to the gluon-gluon fusion mechanism of the
conventional parton model. In phenomenological application, we employ a
parameterization of the dipole cross section which also includes higher order
and saturation effects, thereby going beyond the parton model. Numerical
calculations in the dipole approach agree well with experimental data on open
charm production over a wide range of energy. Dipole approach and next to
leading order parton model yield similar values for open charm production, but
for open bottom production, the dipole approach tends to predict somewhat
higher cross sections than the parton model.Comment: 16 pages, 4 figure
Exclusive Nonleptonic Decays of Bottom and Charm Baryons in a Relativistic Three-Quark Model: Evaluation of Nonfactorizing Diagrams
Exclusive nonleptonic decays of bottom and charm baryons are studied within a
relativistic three-quark model with a Gaussian shape for the momentum
dependence of the baryon-three-quark vertex. We include factorizing as well as
nonfactorizing contributions to the decay amplitudes. For heavy-to-light
transitions Q -> q u d the total contribution of the nonfactorizing diagrams
amount up to approximately 60% of the factorizing contributions in amplitude,
and up to approximately 30% for b -> c u d transitions. We calculate the rates
and the polarization asymmetry parameters for various nonleptonic decays and
compare them to existing data and to the results of other model calculations.Comment: 49 pages, LaTeX-fil
Effective Functional Form of Regge Trajectories
We present theoretical arguments and strong phenomenological evidence that
hadronic Regge trajectories are essentially nonlinear and can be well
approximated, for phenomenological purposes, by a specific square-root form.Comment: 29 pages, LaTeX. Published versio
Multibaryons with heavy flavors in the Skyrme model
We investigate the possible existence of multibaryons with heavy flavor
quantum numbers using the bound state approach to the topological soliton model
and the recently proposed approximation for multiskyrmion fields based on
rational maps. We use an effective interaction lagrangian which consistently
incorporates both chiral symmetry and the heavy quark symmetry including the
corrections up to order 1/m_Q. The model predicts some narrow heavy flavored
multibaryon states with baryon number four and seven.Comment: 8 pages, no figures, RevTe
Studies of correlations between D and mesons in high energy photoproduction
Studies of correlations for a large sample of events containing
fully and partially reconstructed pairs of charmed mesons recorded by the
Fermilab photoproduction experiment FOCUS (FNAL-E831) are presented.
Correlations between and mesons are used to study heavy quark
production dynamics. We present results for fully and partially reconstructed
charm pairs and comparisons to a recent version of \textsc{Pythia} with default
parameter settings. We also comment on the production of in our
data.Comment: 14 pages, 4 figure
- …