105 research outputs found
at finite density
We study the decay channels of the in a nuclear medium and
find a sizable change - of the order of factor five - of the width of this
hyperon at normal nuclear matter density. The mass shift of the
is moderate.Comment: Presented at Particles and Nuclei International Conference (PANIC
05), Santa Fe, New Mexico, 24-28 Oct 200
Exclusive pion electroproduction off nucleons and nuclei
We present our results for the exclusive electroproduction of pions off
nucleons and nuclei at high values of . In electroproduction of nuclei
we consider the Color Transparency (CT) effect recently observed
at JLAB. It is shown that the description of production off nucleons is
mandatory for the proof of the CT signal at JLAB. We further develop the models
for exclusive production of off nucleons at JLAB and HERMES. At first we
describe a model based on exclusive-inclusive connection. In the second
approach we combine a Regge pole approach with the residual effect of nucleon
resonances. The nucleon resonances are described using a dual connection
between the exclusive form factors and inclusive deep inelastic structure
functions. We present the results for the beam spin azimuthal asymmetries
measured at JLAB in exclusive electroproduction of charged and neutral pions.Comment: 15 pages, 10 figures. Invited talk at the NAPP 2010 - 3rd
International Conference on Nuclear and Particle Physics with CEBAF, October
3rd to 8th 2010, Dubrovnik, Croati
Resonance-Parton Duality in off Nucleons
Regge-pole based descriptions of pion-electroproduction on nucleons have
given a very good description of the longitudinal components of the cross
sections. However, these very same models grossly underestimate the transverse
components. A related problem appears in QCD-based scaling arguments that
predict the predominance of longitudinal over transverse electroproduction of
pions by terms . However, data from JLAB, Cornell and DESY,
covering a wide kinematical range and , do not show this expected behavior. We address here
this issue of the transverse response in pion-electroproduction by considering
the contributions of high-lying ( GeV) nucleon resonances to pion
production. The coupling strengths and form factors are obtained through
resonance-parton duality. We show that in a wide range of electron energies and
four-momentum transfers such a model describes all the available data very
well.Comment: Proc. Erice School 2001: "From Quarks and Gluons to Hadrons and
Nuclei", Sept. 16 - 24, 2011, Erice, Ital
dependence of the - and -induced production of the from nuclei
Using results of a recent calculation of the in the nuclear
medium, which show that the medium width is about five times the free width, we
study the A dependence of the production cross section in the
reactions and . We find a sizable A dependence in the ratio of the
nuclear cross sections for heavy nuclei with respect to a light one due to the
large value of the width in the medium, showing that devoted
experiments, easily within reach in present facilities, can provide good
information on that magnitude by measuring the cross sections studied here.Comment: 14 pages, 5 figure
Deep exclusive electroproduction of at HERMES
Deeply virtual electroproduction of pion in exclusive reaction
is studied using a two-component model which includes soft
hadronic and hard partonic reaction mechanisms. The results are compared with
the experimental data measured at HERMES in the deep inelastic region for
values of GeV and GeV. At forward angles the
cross section is longitudinal and is dominated by exchange of Regge poles, with
the dominant trajectory. The off-forward region with GeV is
transverse and shows the dominance of partonic subprocesses. An implication of
present results for the future JLAB facilities are briefly discussed.Comment: 10 pages, 4 figure
Deep exclusive charged electroproduction above the resonance region
A description of exclusive charged pion electroproduction
off nucleons at high energies is proposed. The model combines a Regge pole
approach with residual effect of nucleon resonances. The exchanges of
(140), vector and axial-vector and
Regge trajectories are considered. The contribution of nucleon resonances is
described using a dual connection between the exclusive hadronic form factors
and inclusive deep inelastic structure functions. The model describes the
measured longitudinal, transverse and interference cross sections at JLAB and
DESY. The scaling behavior of the cross sections is in agreement with JLAB and
deeply virtual HERMES data. The results for a polarized beam-spin azimuthal
asymmetry in are presented. Model predictions for JLAB
at 12 GeV are given.Comment: 29 page
Color transparency in hadronic attenuation of rho0 mesons
Ongoing experiments at JLAB investigate the nuclear transparency in exclusive
rho0(770) electroproduction off nuclei. In this work we present transport model
predictions for the attenuation of rho0s in nuclei and for color transparency
(CT) effects as observable at CLAS with a 5 GeV electron beam energy. A full
event simulation presented here permits to study the impact of actual
experimental acceptance conditions and kinematical cuts. The exclusive
(e,e'rho0) cross section off nucleons is described by diffractive and color
string breaking mechanisms extended toward the onset of the deep inelastic
regime. Different hadronization and CT scenarios are compared. We show that a
detailed analysis of elementary cross section, nuclear effects and experimental
cuts is needed to reveal the early onset of rho0-CT at present JLAB energies.Comment: 10 pages, 11 figure
and in the nuclear medium
Recent studies of the resonance within chiral unitary theory
with coupled channels find the resonance as a dynamically generated state from
the interaction of the decuplet of baryons and the octet of mesons, essentially
a quasibound state of in this case, although the coupling
of the to the and makes this picture
only approximate. The decay channel of the
is forbidden in free space for the nominal mass of the , but
the coupling of the to components in the nuclear medium opens new
decay channels of the in the nucleus and produces a much larger
width. Together with medium modifications of the and
decay channels, the final width of the at nuclear matter
density is more than five times bigger than the free one. We perform the
calculations by dressing simultaneously the and the
resonances, finding moderate changes in the mass but
substantial ones in the width of both resonances.Comment: 20 pages, 6 figures; comparison made to data, new references and new
(small) decay channel include
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