35 research outputs found
Study of polarization observables in double pion photoproduction on the proton
Using a model for two pion photoproduction on the proton previously tested in
total cross sections and invariant mass distributions, we evaluate here
polarization observables on which recent experiments are providing new
information. We evaluate cross sections for spin 1/2 and 3/2, which are
measured at Mainz and play an important role in tests of the GHD sum rule.
We also evaluate the proton polarization asymmetry which is
currently under investigation at GRAAL in Grenoble.Comment: 23 pages, 14 ps figure
Photoproduction of meson and baryon resonances in a chiral unitary approach
By means of a coupled channel non-perturbative unitary approach, it is
possible to extend the strong constrains of Chiral Perturbation Theory to
higher energies. In particular, it is possible to reproduce the lowest lying
resonances in meson-meson scattering up to 1.2 GeV using the parameters of the
O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be
tackled along similar lines. We report on an update of these results showing
some examples of photon induced reactions where the techniques have been
recently applied.Comment: Contribution to the Erice Summer School of Nuclear Physics, 21th
course: Electromagnetic Probes and the Structure of Hadrons and Nuclei
September 17th - 25th, 1999, Erice/Sicily/Ital
NN coupling and two-pion photoproduction on the nucleon
Effects of non-resonant photoproductions arising from two different
couplings are investigated in the reaction. We find that
the pseudoscalar (PS) coupling is generally preferable to the
pseudovector (PV) coupling and particularly the total cross sections
are successfully described by the model with the PS coupling. In order
to see the difference between the two couplings, we also show the results of
invariant mass spectra and helicity-dependent cross sections in various isospin
channels calculated with the PS and PV couplings.Comment: 35 pages, 11 figures, minor changes and version to be published in
Phys.Rev.
Analysis of CLAS data on double charge pion electroproduction
Recent developments in phenomenological analysis of the CLAS data on 2
electroproduction are presented. The contributions from isobar channels and
, electrocouplings at from 0.25 to 0.6
GeV were determined from the analysis of comprehensive data on differential
and fully integrated 2 cross sections. Experiment Numbers: E94-005 Group:
Hall BComment: Paper compiled for NSTAR2007 meetin
Recent progress on the chiral unitary approach to meson meson and meson baryon interactions
We report on recent progress on the chiral unitary approach, analogous to the
effective range expansion in Quantum Mechanics, which is shown to have a much
larger convergence radius than ordinary chiral perturbation theory, allowing
one to reproduce data for meson meson interaction up to 1.2 GeV. Applications
to physical processes so far unsuited for a standard chiral perturbative
approach are presented. Results for the extension of these ideas to the meson
baryon sector are discussed, together with applications to kaons in a nuclear
medium and atoms.Comment: Contribution to the KEK Tanashi Symposium on Physics of Hadrons and
Nuclei, Tokyo, December 1998, 10 pages, 3 postscript figures. To be published
as a special issue of Nuclear Physics
On the background in the reaction and mixed event simulation
In this paper we evaluate sources of background for the , with the detected through its decay channel, to
compare with the experiment carried out at ELSA. We find background from
followed by decay of a into two ,
recombining one and one , and from the reaction with subsequent decay of the into two photons. This
background accounts for the data at invariant masses beyond 700
MeV, but strength is missing at lower invariant masses which was attributed to
photon misidentification events, which we simulate to get a good reproduction
of the experimental background. Once this is done, we perform an event mixing
simulation to reproduce the calculated background and we find that the method
provides a good description of the background at low invariant
masses but fakes the background at high invariant masses, making background
events at low invariant masses, which are due to misidentification
events, responsible for the background at high invariant masses which is due to
the and reactions.Comment: 10 pages, 5 figure
The role of Delta(1700) excitation and rho production in double pion photoproduction
Recent information on invariant mass distributions of the reaction, where previous theoretical models had shown
deficiencies, have made more evident the need for new mechanisms, so far
neglected or inaccurately included. We have updated a previous model to include
new necessary mechanisms. We find that the production of the meson, and
the excitation, through interference with the dominant terms,
are important mechanisms that solve the puzzle of the
reaction without spoiling the early agreement with the and reactions.Comment: 39 pages, 13 figures (ps files). Final version. To be published in
Nucl. Phys.
Chiral Unitary Approach To The N*N*pi, N*N*eta Couplings For The N*(1535) Resonance
Using a chiral unitary model in which the negative parity nucleon resonance
is generated dynamically by means of the Bethe
Salpeter equation with coupled meson baryon channels in the sector, we
have obtained the and couplings. The
coupling has smaller strength and the same sign as the
coupling. This rules out the mirror assignment of chiral symmetry
where the ground state nucleon and the negative parity resonance
are envisaged as chiral partners in the baryon sector.Comment: 30 pages, 15 figures (ps files). The new version discusses pi-N
scattering around the N*(1535) resonanc
Line Graphs of Weighted Networks for Overlapping Communities
In this paper, we develop the idea to partition the edges of a weighted graph
in order to uncover overlapping communities of its nodes. Our approach is based
on the construction of different types of weighted line graphs, i.e. graphs
whose nodes are the links of the original graph, that encapsulate differently
the relations between the edges. Weighted line graphs are argued to provide an
alternative, valuable representation of the system's topology, and are shown to
have important applications in community detection, as the usual node partition
of a line graph naturally leads to an edge partition of the original graph.
This identification allows us to use traditional partitioning methods in order
to address the long-standing problem of the detection of overlapping
communities. We apply it to the analysis of different social and geographical
networks.Comment: 8 Pages. New title and text revisions to emphasise differences from
earlier paper
Photoproduction of the Lambda(1405) on the proton and nuclei
We study the gamma p ---> K^+ Lambda(1405) reaction at energies close to
threshold using a chiral unitary model where the resonance is generated
dynamically from K^-p interaction with other channels constructed from the
octets of baryons and mesons. Predictions are made for cross sections into
several channels and it is shown that the detection of the K^+ is sufficient to
determine the shape and strength of the Lambda(1405) resonance. The
determination of the resonance properties in nuclei requires instead the
detection of the resonance decay channels. Pauli blocking effects on the
resonance, which have been shown to be very important for the resonance at rest
in the nucleus, are irrelevant here where the resonance is produced with a
large momentum. The nuclear modifications here would thus offer information on
the resonance and K^- nucleus dynamics complementary to the one offered so far
by K^- atoms.Comment: 9 pages, 4 postscripts figure