469 research outputs found
Recent developments in chiral dynamics of hadrons and hadrons in a nuclear medium
In this talk I present recent developments in chiral dynamics of hadrons and
hadrons in a medium addressing the following points: interaction of the octet
of pseudoscalar mesons with the octet of baryons of the nucleon, showing recent
experimental evidence on the existence of two states, the
interaction of the octet of pseudoscalar mesons with the decuplet of baryons of
the , with particular emphasis on the resonance,
dynamically generated by this interaction. Then I review the interaction of
kaons in a nuclear medium and briefly discuss the situation around the claims
of deeply bound states in nuclei. The large renormalization of the
in the nuclear medium is shown as another example of successful
application of the chiral unitary techniques.Comment: Talk at the Fifth International Conference on Perspectives in
Hadronic Physics: Particle-Nucleus and Nucleus-Nucleus Scattering at
Relativistic Energies, Trieste, May 200
Lineshape of the Lambda(1405) Hyperon Measured Through its Sigma0 pion0 Decay
The pp -> p K+ Y0 reaction has been studied for hyperon masses m(Y0)<1540
MeV/c2 at COSY-Juelich by using a 3.65 GeV/c circulating proton beam incident
on an internal hydrogen target. Final states comprising two protons, one
positively charged kaon and one negatively charged pion have been identified
with the ANKE spectrometer. Such configurations are sensitive to the production
of the ground state Lambda and Sigma0 hyperons as well as the Sigma0(1385) and
Lambda(1405) resonances. Applying invariant- and missing-mass techniques, the
two overlapping excited states could be well separated, though with limited
statistics. The shape and position of the Lambda(1405) distribution,
reconstructed cleanly in the Sigma0 pion0 channel, are similar to those found
from other decay modes and there is no obvious mass shift. This finding
constitutes a challenging test for models that predict Lambda(1405) to be a
two-state resonance.Comment: 10 pages, 4 figures, accepted for publication in Phys. Lett.
UCLA Intermediate Energy Nuclear and Particle Physics Research: Final Report
This project covers the following research: (a) Investigations into the structure of the proton and neutron. This is done by investigating the different resonance states of nucleons with beams of tagged, polarized photons, linearly as well as circularly, incident on polarized hydrogen/deuterium targets and measuring the production of {pi}{sup #25;0}, 2{pi}{sup #25;}0, 3{pi}{sup #25;0}, {eta}#17;, {eta}', {omega}, etc. The principal detector is the Crystal Ball multiphoton spectrometer which has an acceptance of nearly 4#25;. It has been moved to the MAMI accelerator facility of the University of Mainz, Germany. We investigate the conversion of electromagnetic energy into mesonic matter and conversely. (b) We investigate the consequences of applying the "standard" symmetries of isospin, GâÂÂparity, charge conjugation, C, P, T, and chirality using rare and forbidden decays of light mesons such as the {eta}#17;,{eta}' and {omega}. We also investigate the consequences of these symmetries being slightly broken symmetries. We do this by studying selected meson decays using the Crystal Ball detector. (c) We determine the mass, or more precisely the mass difference of the three light quarks (which are inputs to Quantum Chromodynamics) by measuring the decay rate of specially selected {eta}#17; and {eta}' decay modes, again we use the Crystal Ball. (d)We have started a new program to search for the 33 missing cascade baryons using the CLAS detector at the Thomas Jefferson Laboratory. Cascade resonances are very special: they have double strangeness and are quite narrow. This implies that they can be discovered by the missing mass technique in photoproduction reactions such as in {gamma}p{yields}{Xi}{sup #4;âÂÂ}K{sup +}K{sup +}. The cascade program is of particular importance for the upgrade to 12 GeV of the CLAS detector and for design of the Hall D at JLab. (e) Finally, we are getting more involved in a new program to measure the hadronic matter form factor of complex nuclei, in particular the "neutron skin" of {sup 208}Pb, which is of great interest to astroparticle physics for determining the properties of neutron stars. Processes of study are coherent and nonâÂÂcoherent #25;0 photoproduction. The Crystal Ball is uniquely suited for these studies because of the large acceptance, good direction and energy resolution and it is an inclusive detector for the #25;{pi}{sup 0} final state and exclusive for background such as 2#25;{pi}{sup 0}
The reaction pi N to pi pi N in a meson-exchange approach
A resonance model for two-pion production in the pion-nucleon reaction is
developed that includes information obtained in the analysis of pion-nucleon
scattering in a meson-exchange model. The baryonic resonances Delta(1232),
N*(1440), N*(1520), N*(1535), and N*(1650) are included. The model reproduces
the total cross sections up to kinetic energies of the incident pion of 350 MeV
and obtains the shapes of the differential cross sections in reasonable
agreement with the data.Comment: 7 pages, 7 figures, 2 table
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.
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
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
- …