357 research outputs found
Separable potential model for interactions at low energies
The effective separable meson-baryon potentials are constructed to match the
equivalent chiral amplitudes up to the second order in external meson momenta.
We fit the model parameters (low energy constants) to the threshold and low
energy data. In the process, the -proton bound state problem is
solved exactly in the momentum space and the 1s level characteristics of the
kaonic hydrogen are computed simultaneously with the available low energy
cross sections. The model is also used to describe the
mass spectrum and the energy dependence of the amplitude.Comment: 31 pages, v2 - added corrections to make it compatible with the
published versio
Chiral dynamics of baryon resonances and hadrons in a nuclear medium
In these lectures I make an introduction to chiral unitary theory applied to
the meson baryon interaction and show how several well known resonances are
dynamically generated, and others are predicted. Two very recent experiments
are analyzed, one of them showing the existence of two
states and the other one providing support for the
resonance as a quasibound state of . The
use of chiral Lagrangians to account for the hadronic interaction at the
elementary level introduces a new approach to deal with the modification of
meson and baryon properties in a nuclear medium. Examples of it for ,
and modification in the nuclear medium are presented.Comment: Lectures given in the Workshop on Hadron Physics, Puri (India), march
200
The pi -> pi pi process in nuclei and the restoration of chiral symmetry
The results of an extensive campaign of measurements of the pi -> pi pi
process in the nucleon and nuclei at intermediate energies are presented. The
measurements were motivated by the study of strong pi pi correlations in
nuclei. The analysis relies on the composite ratio C_{pi pi}^A, which accounts
for the clear effect of the nuclear medium on the (pi pi) system. The
comparison of the C_{pi pi}^A distributions for the (pi pi)_{I=J=0} and (pi
pi)_{I=0,J=2} systems to the model predictions indicates that the C_{pi pi}^A
behavior in proximity of the 2m_pi threshold is explainable through the partial
restoration of chiral symmetry in nuclei.Comment: accepted for publication in Nucl. Phys.
Exploration of hyperfine interaction between constituent quarks via eta productions
In this work, the different exchange freedom, one gluon, one pion or
Goldstone boson, in constituent quark model is investigated, which is
responsible to the hyperfine interaction between constituent quarks, via the
combined analysis of the eta production processes,
and . With the Goldstone-boson exchange, as well as
the one-gluon or one-pion exchange, both the spectrum and observables, such as,
the differential cross section and polarized beam asymmetry, are fitted to the
suggested values of Particle Data Group and the experimental data. The first
two types of exchange freedoms give acceptable description of the spectrum and
observables while the one pion exchange can not describe the observables and
spectrum simultaneously, so can be excluded. The experimental data for the two
processes considered here strongly support the mixing angles for two lowest S11
sates and D13 states as about -30 and 6 degree respectively.Comment: 7 pages, 4 figures, 4 table
The cusp effect in eta' --> eta pi pi decays
Strong final-state interactions create a pronounced cusp in eta' --> eta pi0
pi0 decays. We adapt and generalize the non-relativistic effective field theory
framework developed for the extraction of pi pi scattering lengths from K --> 3
pi decays to this case. The cusp effect is predicted to have an effect of more
than 8% on the decay spectrum below the pi+ pi- threshold.Comment: 11 pages, 8 figures; comment added, typos corrected, version
published in Eur. Phys. J.
Penta-quark states with hidden charm and beauty
More and more hadron states are found to be difficult to be accommodated by
the quenched quark models which describe baryons as 3-quark states and mesons
as antiquark-quark states. Dragging out an antiquark-quark pair from the gluon
field in hadrons should be an important excitation mechanism for hadron
spectroscopy. Our recent progress on the penta-quark states with hidden charm
and beauty is reviewed.Comment: Plenary talk at the 5th Asia-Pacific Conference on Few-Body Problems
in Physics 2011 (APFB2011), 22-26 Aug., 2011, Seoul, Kore
Measurement of Inverse Pion Photoproduction at Energies Spanning the N(1440) Resonance
Differential cross sections for the process pi^- p -> gamma n have been
measured at Brookhaven National Laboratory's Alternating Gradient Synchrotron
with the Crystal Ball multiphoton spectrometer. Measurements were made at 18
pion momenta from 238 to 748 MeV/c, corresponding to E_gamma for the inverse
reaction from 285 to 769 MeV. The data have been used to evaluate the gamma n
multipoles in the vicinity of the N(1440) resonance. We compare our data and
multipoles to previous determinations. A new three-parameter SAID fit yields 36
+/- 7 (GeV)^-1/2 X 10^-3 for the A^n_1/2 amplitude of the P_11.Comment: 14 pages, 8 figures, submitted to PR
The nature of the Lambda(1405)
We present here some results supporting the nature of the
resonance as dynamically generated from the meson baryon interaction in coupled
channels and resulting from the superposition of two close-by poles. We find
support for this picture in the reaction,
which shows a different shape than the one obtained from the reaction. We also call the attention to the with in the region, which shows a narrow
peak in the calculations around 1420 MeV. We also report on recent calculations
of the radiative decay of the two states and on reactions to
obtain information on these decay modes. Finally, we present results for the
reaction recently measured at ANKE/COSY and compare
them with theoretical results.Comment: Talk given at the NSTAR2007 Workshop, Bonn September 200
Dynamically generated resonances from the vector octet-baryon decuplet interaction
We study the interaction of the octet of vector mesons with the decuplet of
baryons using Lagrangians of the hidden gauge theory for vector interactions.
The unitary amplitudes in coupled channels develop poles that can be associated
with some known baryonic resonances, while there are predictions for new ones
at the energy frontier of the experimental research. The work offers guidelines
on how to search for these resonances
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