arXiv
(422.153 recursos)
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Mostrando recursos 1 - 20 de 17.953
1.
Medium induced jet absorption at relativistic heavy ion collisions - Drees, Axel; Feng, Haidong; Jia, Jiangyong
The dense medium created in Au + Au collisions at the Relativistic Heavy-Ion
Collider (RHIC) significantly suppresses particle production from hard
scattering processes and their characteristic back-to-back angular correlation.
We present a simple model of jet absorption in dense matter which incorporates
a realistic nuclear geometry. Our calculations are performed at the jet level
and assume independent jet fragmentation in the vacuum. This model describes
quantitatively the centrality dependence of the observed suppression of the
high $p_T$ hadron yield and of the back-to-back angular correlations. The
azimuthal anisotropy of high $p_T$ particle production can not be accounted for
using a realistic nuclear geometry.
2.
A new look at nuclear supersymmetry though transfer experiments - Barea, J.; Bijker, R.; Frank, A.
Nuclear supersymmetry is reviewed and some of its applications and extensions
are discussed, together with a proposal for new, more stringent and precise
tests to probe the supersymmetry classification, in particular, correlations
between nuclei that belong to the same supermultiplet. The combination of these
theoretical and experimental studies may play a unifying role in nuclear
phenomena
3.
Quark structure and nuclear effective forces - Guichon, P. A. M.; Thomas, A. W.
We formulate the quark meson coupling model as a many-body effective
Hamiltonian. This leads naturally to the appearance of many-body forces. We
investigate the zero range limit of the model and compare its Hartree-Fock
Hamiltonian to that corresponding to the Skyrme effective force. By fixing the
three parameters of the model to reproduce the binding and symmetry energy of
nuclear matter, we find that it allows a very satisfactory interpretation of
the Skyrme force.
4.
New treatment of the chiral SU(3) quark mean field model - Wang, P.; Leinweber, D. B.; Thomas, A. W.; Williams, A. G.
We perform a study of infinite hadronic matter, finite nuclei and hypernuclei
with an improved method of calculating the effective baryon mass. A detailed
study of the predictions of the model is made in comparison with the available
data and the level of agreement is generally very good. Comparison with an
earlier treatment shows relatively minor differences at or below normal nuclear
matter density, while at high density the improved calculation is quite
different. In particular, we find no phase transition corresponding to chiral
symmetry restoration in high density nuclear matter.
5.
Neutral-current neutrino-nucleus quasielastic scattering - Meucci, Andrea; Giusti, Carlotta; Pacati, Franco Davide
A relativistic distorted-wave impulse-approximation model to quasielastic
neutral-current neutrino-nucleus scattering is developed, using the
relativistic mean field theory for the bound state and taking into account the
final state interaction in the relativistic scattering state. Results for the
neutrino (antineutrino) reaction on 12C target nucleus are presented in an
energy range between 500 and 1000 MeV. The sensitivity to the strange quark
content of the axial-vector form factor is discussed.
6.
The Caloric Curve for Mononuclear Configurations - Sobotka, L. G.; Charity, R. J.; Toke, J.; Schroder, W. U.
The caloric curve for mononuclear configurations is studied with a schematic
model. We investigate the dependence of the entropy on the density and
effective mass profiles. A plateau in the caloric curve is a direct result of
decreasing density and the destruction of correlations with increasing
excitation. The mononuclear regime is metastable with respect to binary fission
at low excitation energy and unstable with respect to multifragmentation at
high excitation. The statistical framework presented here is suitable to treat
scenarios where experimental conditions are set to favor population of highly
excited mononuclear states.
7.
Bounds on the bound \eta ^3He system - Sibirtsev, A.; Haidenbauer, J.; Niskanen, J. A.; Meißner, Ulf-G.
We investigate the relation between the \eta ^3He binding energy and width
and the (complex) \eta ^3He scattering length. Following our systematic
analysis of the eta 3He scattering length we set limits on the \eta ^3He
binding. If bound states exist the binding energy (width) should not exceed 5
MeV (10 MeV). In addition, we comment on a recently claimed observation of an
\eta-mesic ^3He quasi-bound state by the TAPS collaboration based on \eta
photoproduction data. Although our limits are in reasonable agreement with the
values reported by this collaboration, our analysis of these data does not lead
to a solid conclusion concerning the existence of an \eta-mesic...
8.
Interaction effects in ${\bm K^+}$ photoproduction on the deuteron - Salam, Agus; Arenhoevel, Hartmuth
Kaon photoproduction on the deuteron is studied with respect to a specific
two-body contribution, namely a pion mediated production process, besides other
final state interaction contributions from kaon-nucleon and hyperon-nucleon
scattering. In this process, a pion is first photoproduced on one nucleon and
then interacts with the spectator nucleon in a strangeness exchange reaction
leading to a kaon and a hyperon. A sizeable effect from this pion mediated
contribution is found, considerably larger than the previously studied
hyperon-nucleon rescattering, whereas kaon-nucleon rescattering is much less
important. Besides total and semi-inclusive differential cross sections, tensor
target asymmetries are studied with respect to the influence of such
interaction effects.
9.
Proton-Neutron Coupling in the Gamow Shell Model: the Lithium Chain - Michel, N.; Nazarewicz, W.; Ploszajczak, M.
The shell model in the complex k-plane (the so-called Gamow Shell Model) has
recently been formulated and applied to structure of weakly bound, neutron-rich
nuclei. The completeness relations of Newton and Berggren, which apply to the
neutron case, are strictly valid for finite-range potentials. However, for
long-range potentials, such as the Coulomb potential for protons, for which the
arguments based on the Mittag-Leffler theory do not hold, the completeness
still needs to be demonstrated. This has been done in this paper, both
analytically and numerically. The generalized Berggren relations are then used
in the first Gamow Shell Model study of nuclei having both valence neutrons and
protons, namely the...
10.
Comment on the $\Theta^+$-production at high energy - Titov, A. I.; Hosaka, A.; Date', S.; Ohashi, Y.
We show that the cross sections of the $\Theta^+$-pentaquark production in
different processes decrease with energy faster than the cross sections of
production of the conventional three-quark hyperons. Therefore, the threshold
region with the initial energy of a few GeV or less seemsto be more favorable
for the production and experimental study of $\Theta^+$-pentaquark.
11.
Photo-emission of two protons from nuclei - Anguiano, Marta; Co', Giampaolo; Lallena, Antonio M.
The photo-emission of two protons from the $^{12}$C, $^{16}$O and $^{40}$Ca
nuclei is investigated. Aim of the work is the study of the possibilities
offered by this probe to obtain information about the characteristics of the
short-range correlations. We have also evaluated the effects of the two-body
$\Delta$-currents which, in this processes, compete with those produced by the
short-range correlations. Our results show that ($\gamma$,pp) processes could
be more useful than (e,e'pp) for the study of the short-range correlations.
12.
Extrapolation method in shell model calculations with deformed basis - Mizusaki, Takahiro
An extrapolation method in shell model calculations with deformed basis is
presented, which uses a scaling property of energy and energy variance for a
series of systematically approximated wave functions to the true one. Such
approximated wave functions are given by variation-after-projection method
concerning the full angular momentum projection. This extrapolation needs
energy variance, which amounts to the calculation of expectation value of
square of Hamiltonian $\hat{H}^2$. We present the method to evaluate this
matrix element and show that large reduction of its numerical computation can
be done by taking an advantage of time-reversal symmetry. The numerical tests
are presented for $fp$ shell calculations with a realistic residual
interaction.
13.
Symmetry energy for fragmentation in dynamical nuclear collisions - Ono, Akira; Danielewicz, P.; Friedman, W. A.; Lynch, W. G.; Tsang, M. B.
We extract values for the free symmetry energy as a function of the fragment
size (the proton number Z) from antisymmetrized molecular dynamics (AMD)
calculations of calcium collisions. Simple statistical physics describe well
the distribution of hot nuclei at breakup, provided the surface symmetry term
in the free energy is much smaller at high excitation than in ground state
nuclei. This result may reflect the condition of low density and finite
temperature when these systems disassemble.
14.
Correlated nucleons in configuration space - Müther, H.; Sick, Ingo
Several recent studies have dealt with the effects of short range
correlations on the momentum distribution of nucleons in nuclei. Here we
investigate the correlation effects on the density and spectral distribution in
coordinate space. A combination of experimental data and spectral functions
calculated from realistic N-N interactions allows us to resolve a recently
uncovered discrepancy with occupation of quasi-particle states derived from
(e,e'p) data.
15.
Entrance channels and alpha decay half-lives of the heaviest elements - Royer, G.; Zbiri, K.; Bonilla, C.
The barriers standing against the formation of superheavy elements and their
consecutive $\alpha$ decay have been determined in the quasimolecular shape
path within a Generalized Liquid Drop Model including the proximity effects
between nucleons in a neck, the mass and charge asymmetry, a precise nuclear
radius and the shell effects given by the Droplet Model. For moderately
asymmetric reactions double-hump potential barriers stand and fast fission of
compact shapes in the outer well is possible. Very asymmetric reactions lead to
one hump barriers which can be passed only with a high energy relatively to the
superheavy element energy. Then, only the emission of several neutrons or an
$\alpha$ particle...
16.
Statistical hadronization with resonances - Torrieri, Giorgio; Letessier, Jean; Rafelski, Johann; Steinke, Steve
We introduce the equilibrium and non-equilibrium statistical hadronization
picture of particle production in ultra-relativistic heavy ion collisions. We
describe the related physical reaction scenarios, and show how these can lead
to quark pair yield non-equilibrium. Using the SHARE1.2 program suite we
quantitatively model particle yields and ratios for RHIC-130 run.
We study how experimental particle ratios can differentiate between model
scenarios, and discuss in depth the importance of hadronic resonances in
understanding of hadron production processes.
17.
Stability and structure of quark matter in a molecular dynamics framework - Akimura, Yuka; Maruyama, Toshiki; Yoshinaga, Naotaka; Chiba, Satoshi
We study stability and structure of quark matters as a function of density in
a framework of molecular dynamics (MD). Using appropriate effective
interactions and the frictional cooling method, we search for the minimum
energy of the system. Transition from confined to deconfined phase is observed
at densities of 2 -- 3$\rho_0$, where $\rho_0$ is the nuclear matter saturation
density. The $uds$ matter becomes more stable than the charge-neutral $ud$
matter at 3$\rho_0$, but the $udd$ matter is the most stable even at high
density.
18.
Kaon and Pion production in relativistic heavy-ion collisions - Wagner, M.; Larionov, A. B.; Mosel, U.
The BUU transport model is applied to study strangeness and pion production
in nucleus-nucleus collisions. Starting from proton induced reactions, we
further investigate Si+Au, Au+Au and Pb+Pb collisions in the energy range
between 2 and 40 A$\cdot$GeV and compare with data and with other transport
calculations. The $q \bar q$ annihilation, or resonance, channel simulated by
the string model in meson-nucleon collisions at $\sqrt{s} > 2$ GeV is
introduced. The importance of this channel for a good description of the
proton-nucleus data on $K^+$ production is demonstrated. We, furthermore, show
that the meson-meson collisions contribute significantly to the $K \bar K$
production in heavy-ion collisions above 5 A GeV...
19.
Phase structure of the two-fluid proton-neutron system - Caprio, M. A.; Iachello, F.
The phase structure of a two-fluid bosonic system is investigated. The
proton-neutron interacting boson model (IBM-2) posesses a rich phase structure
involving three control parameters and multiple order parameters. The surfaces
of quantum phase transition between spherical, axially-symmetric deformed, and
SU*(3) triaxial phases are determined.
20.
Perturbative HFB model for many-body pairing correlations - Hagino, K.; Sagawa, H.
We develop a perturbative model to treat the off-diagonal components in the
Hartree-Fock-Bogoliubov (HFB) transformation matrix, which are neglected in the
BCS approximation. Applying the perturbative model to a weakly bound nucleus
$^{84}$Ni, it is shown that the perturbative approach reproduces well the
solutions of the HFB method both for the quasi-particle energies and the radial
dependence of quasi-particle wave functions. We find that the non-resonant part
of the continuum single-particle state can acquire an appreciable occupation
probability when there exists a weakly bound state close to the Fermi surface.
This result originates from the strong coupling between the continuum particle
state and the weakly bound state, and is...
1.
