748 research outputs found
Relativistic Hartree approach including both positive- and negative-energy bound states
We develop a relativistic model to describe the bound states of positive
energy and negative energy in finite nuclei at the same time. Instead of
searching for the negative-energy solution of the nucleon's Dirac equation, we
solve the Dirac equations for the nucleon and the anti-nucleon simultaneously.
The single-particle energies of negative-energy nucleons are obtained through
changing the sign of the single-particle energies of positive-energy
anti-nucleons. The contributions of the Dirac sea to the source terms of the
meson fields are evaluated by means of the derivative expansion up to the
leading derivative order for the one-meson loop and one-nucleon loop. After
refitting the parameters of the model to the properties of spherical nuclei,
the results of positive-energy sector are similar to that calculated within the
commonly used relativistic mean field theory under the no-sea approximation.
However, the bound levels of negative-energy nucleons vary drastically when the
vacuum contributions are taken into account. It implies that the
negative-energy spectra deserve a sensitive probe to the effective interactions
in addition to the positive-energy spectra.Comment: 38 pages, Latex, 8 figures included; Int. J. Mod. Phys. E, in pres
Bound states of anti-nucleons in finite nuclei
We study the bound states of anti-nucleons emerging from the lower continuum
in finite nuclei within the relativistic Hartree approach including the
contributions of the Dirac sea to the source terms of the meson fields. The
Dirac equation is reduced to two Schr\"{o}dinger-equivalent equations for the
nucleon and the anti-nucleon respectively. These two equations are solved
simultaneously in an iteration procedure.
Numerical results show that the bound levels of anti-nucleons vary
drastically when the vacuum contributions are taken into account.Comment: 8 pages, no figures. Proceedings of International Conference on
Nonequilibrium and Nonlinear Dynamics in Nuclear and Other Finite Systems,
Beijing, China 2001; AIP conference proceedings 597, edited by Zhuxia Li, Ke
Wu, Xizhen Wu, Enguang Zhao, and F. Sakata (Melville, New York, 2001) page
112-11
Expectations of fragment decay from highly excited nuclei
The statistical model is used to illustrate the consequences of a successive binary decay mechanism as the initial nuclear excitation is pushed towards the limits of stability. The partition of the excitation energy between light and heavy fragments is explicitly calculated, as are the consequences of the decay of the primary light fragments to particle-bound residual nuclei which would be observed experimentally. The test nucleus 100 44 Ru is considered at initial excitations of 100, 200, 400, and 800 MeV. Exit channels of n, p, and α; and 100 clusters of 3 †Z †20 †4, 6 †A †48 are considered from all nuclides in the deexcitation cascade. The total primary and final cluster yields are shown versus Z and initial excitation. The primary versus final yields are also shown individually for 12C, 26Mg, and 48Ca. We show how multifragmentation yields will change with the excitation energy due to a successive binary decay mechanism. Measurements that may be prone to misinterpretation are discussed, as are those that should be representative of initial nucleus excitation
Energy Spectra of Anti-nucleons in Finite Nuclei
The quantum vacuum in a many-body system of finite nuclei has been
investigated within the relativistic Hartree approach which describes the bound
states of nucleons and anti-nucleons consistently. The contributions of the
Dirac sea to the source terms of the meson-field equations are taken into
account up to the one-nucleon loop and one-meson loop. The tensor couplings for
the - and -meson are included in the model. The overall nucleon
spectra of shell-model states are in agreement with the data. The calculated
anti-nucleon spectra in the vacuum differ about 20 -- 30 MeV with and without
the tensor-coupling effects.Comment: 4 pages, to appear in the Proceedings of MENU 2004 (Beijing, Aug. 29
-- Sept. 4, 2004
Using two- and Three-particle correlations to probe strongly interacting partonic matter
The latest two- and three-particle correlation measurements obtained by the
PHENIX collaboration are presented. Three-particle correlations are consistent
with the presence of conical emission patterns in the data. Two-particle
correlations relative to the collision geometry reveal strong shape and yield
modifications of the away-side jet, that depend on the orientation of the
trigger particle with respect to the event plane. A difference in the geometry
dependence of the per trigger yields in the regions around and can be understood by a different
geometry dependence of jet energy loss and the medium response to the deposited
energy.Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Dynamical treatment of Fermi motion in a microscopic description of heavy ion collisions
A quasiclassical Pauli potential is used to simulate the Fermi motion of nucleons in a molecular dynamical simulation of heavy ion collisions. The thermostatic properties of a Fermi gas with and without interactions are presented. The inclusion of this Pauli potential into the quantum molecular dynamics (QMD) approach yields a model with well defined fermionic ground states, which is therefore also able to give the excitation energies of the emitted fragments. The deexcitation mechanisms (particle evaporation and multifragmentation) of the new model are investigated. The dynamics of the QMD with Pauli potential is tested by a wide range of comparisons of calculated and experimental double-differential cross sections for inclusive p-induced reactions at incident energies of 80 to 160 MeV. Results at 256 and 800 MeV incident proton energy are presented as predictions for completed experiments which are as yet unpublished
Second Cluster Integral and Excluded Volume Effects for the Pion Gas
The quantum mechanical formula for Mayer's second cluster integral for the
gas of relativistic particles with hard-core interaction is derived. The proper
pion volume calculated with quantum mechanical formula is found to be an order
of magnitude larger than its classical evaluation.
The second cluster integral for the pion gas is calculated in quantum
mechanical approach with account for both attractive and hard-core repulsive
interactions. It is shown that, in the second cluster approximation, the
repulsive pion-pion-interactions as well as the finite width of resonances give
important but almost canceling contributions. In contrast, an appreciable
deviation from the ideal gas of pions and pion resonances is observed beyond
the second cluster approximation in the framework of the Van der Waals
excluded-volume model.Comment: 29 pages, Latex, 9 PS-figure
Hypermatter in chiral field theory
We investigate the properties of hadronic matter and nuclei be means of a
generalized model with broken scale invariance. In
mean-field approximation, vector and scalar interactions yield a saturating
nuclear equation of state. Finite nuclei can be reasonably described, too. The
condensates and the effective baryon masses at finite baryon density and
temperature are discussed.Comment: uses IOP style, to be published in Journal of Physics, Proceedings of
the International Symposium on Strangeness in Quark Matter 1997, April 14-18,
Thera (Santorini), Hella
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