19 research outputs found
Pluto: A Monte Carlo Simulation Tool for Hadronic Physics
Pluto is a Monte-Carlo event generator designed for hadronic interactions
from Pion production threshold to intermediate energies of a few GeV per
nucleon, as well as for studies of heavy ion reactions. This report gives an
overview of the design of the package, the included models and the user
interface.Comment: XI International Workshop on Advanced Computing and Analysis
Techniques in Physics Research, April 23-27 2007, Amsterdam, the Netherland
- nucleus bound states in Walecka model
Possible formation of nucleus bound state is studied in the framework
of Walecka model. The bound states are found in different nuclei ranging from
to . These bound states may have a direct bearing on the
recent experiments on the photoproduction of meson in the nuclear
medium.Comment: RevTeX fil
Subthreshold rho^0 photoproduction on 3He
A large reduction of the rho^0 mass in the nuclear medium is reported,
inferred from dipion photoproduction spectra in the 1 GeV region, for the
reaction 3He(gamma,pi+ pi-)X with a 10% duty factor tagged-photon beam and the
TAGX multi-particle spectrometer. The energy range covered (800 < E(gamma) <
1120 MeV) lies mostly below the free rho^0 production threshold, a region which
is believed sensitive to modifications of light vector-meson properties at
nuclear-matter densities. The rho^0 masses extracted from the MC fitting of the
data, m*(rho^0) = 642 +/- 40, 669 +/- 32, and 682 +/- 56 MeV/c^2 for E(gamma)
in the 800-880, 880-960, and 960-1040 MeV regions respectively, are
independently corroborated by a measured, assumption-free, kinematical
observable. This mass shift, far exceeding current mean-field driven
theoretical predictions, may be suggestive of rho^0 decay within the range of
the nucleonic field.Comment: 40 pages, 13 figures, submitted to Phys. Rev.
Observation of Meson Modification in Nuclear Matter
We have measured invariant mass spectra of electron-positron pairs in the
target rapidity region of 12GeV p+A reactions. We have observed a significant
difference in the mass spectra below the meson between p+C and p+Cu
interactions. The difference is interpreted as a signature of the
modification at normal nuclear-matter density.Comment: 8 pages, 3 figures, submitted to Phys. Rev. Letters. all the figures
changed to Postscript format, text not change
Probing the DeltaNN component of 3He
The 3He(gamma,pi^+/- p) reactions were measured simultaneously over a tagged
photon energy range of 800<E_gamma<1120 MeV, well above the Delta resonance
region. An analysis was performed to kinematically isolate Delta knockout
events from conventional Delta photoproduction events, and a statistically
significant excess of pi+p events was identified, consistent with Delta++
knockout. Two methods were used to estimate the DeltaNN probability in the 3He
ground state, corresponding to the observed knockout cross section. The first
gave a lower probability limit of 1.5+/-0.6+/-0.5%; the second yielded an upper
limit of about 2.6%.Comment: 14 page
Production and decay of the d* dibaryon
The production of the isoscalar Jp = 3+ didelta dibaryon d* by proton
inelastic scattering from deuteron targets is described in a double-scattering
Glauber approximation. Each scattering changes a target nucleon into a Delta
with the help of the isovector tensor force transmitted by pi and rho mesons.
The differential cross section constructed from empirical Love-Franey
nucleon-nucleon t-matrices and a simple model of d* shows a maximum of some 10
micro-b/sr at 70 deg (c.m.) for 500 MeV protons. The partial width of the decay
d* -> NN caused by the exchanges of the same mesons is found for this simple
model of d* to be about 9 MeV if the d* mass is 2100 MeV. The implications of
these results are discussed.Comment: 31 pages, 8 figure
Effective Vector Meson Masses in a Cutoff Field Theory
Based on quantum hadrodynamics with a finite cutoff, the effective masses of
vector mesons(\omega, \rho) in nuclear medium are calculated. We use a
low-energy effective Lagrangian which is obtained by integrating high-energy
quantum fluctuations. Although we use an artificial cutoff, the
cutoff-dependence can be removed order by order. It is shown that there is a
strong correlation between the effective \omega -meson mass and the effective
nucleon mass at the normal density. It is also found that the effective
\rho-meson mass m_\rho^* decreases as density increases. The rate of the
decrease becomes smaller at high density. As a result, at the normal density,
the m^*_\rho/m_\rho is 0.85 \sim 0.95.Comment: 15 pages, LateX, 7 eps figures. Email: [email protected]