Classical microscopic calculation of fast heavy-ion collisions

We consider heavy-ion collisions with beam energies of a few hundred MeV/nucleon, because such collisions seem favorable for producing compressed nuclear matter. As an alternative to hydrodynamic ways of calculating such collisions, we are investigating a microscopic, rapid (and therefore economical) simulation method. There are two simplifications basic to this method: (i) using classical particle kinematics, and (ii) taking nucleonnucleon interactions into account via cross sections rather than explicit forces. Some other simplifications, concerning nuclear binding etc., are presently crude but will be improved. Even at normal density, nuclear matter is not so dilute; therefore our calculations show some sensitivity to details of the mechanism assume for nucleon-nucleon scattering. For head-on collision of two mass-235 nuclei, our present calculations yield maximum densities between 2 and 3 times that of normal nuclear matter.     

Strangeness production in proton—proton and proton—nucleus collisions

We discuss the investigation of the strange meson production in proton-proton (pp) and proton-nucleus (pA) reactions within an effective Lagrangian model. The kaon production proceeds mainly via excitations ofN*(1650),N*(1710), andN* (1720) resonant intermediate nucleonic states, in the collision of two initial state nucleons. Therefore, the strangeness production is expected to provide information about the resonances lying at higher excitation energies. For beam energies very close to the kaon production threshold the hyperon-proton final state interaction effects are quite important. Thus, these studies provide a check on the models of hyperon-nucleon interactions. The inmedium production of kaons shows strong sensitivity to the self-energies of the intermediate mesons     

Classical trajectory calculations with time-dependent forces in heavy-ion collisions

The applicability of a phenomenological time-dependent nucleus-nucleus potential to deep inelastic collisions is studied. We present its general shape and make a particular choice of the diabatic and adiabatic parts. From trajectory calculations we find that the angle-energy correlation is well described when a time-dependent friction force is used. We also compare our results to some TDHF calculations.     

Non-adiabatic calculation of muonic atom-nucleus collisions

In order to calculate the cross sections of the muonic atom-nucleus collisions, we have proposed a precise numerical method, a non-adiabatic coupled-rearrangement-channel method with the use of the Jacobian coordinates for the three-body system in the whole space. The scattering boundary condition is correctly imposed along the coordinates; this method does not suffer from the well known defects of the method of adiabatic representation. We applied our method to the muonic atom-nucleus collisions for an incident c.m. energies of 0.001–100 eV.     

Heavy quark energy loss in proton proton collisions at LHC

A promising probe to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. Experiments at the Relativistic Heavy Ion Collider (RHIC) have shown that heavy quarks, i.e. charm and bottom quarks show a remarkable high momentum suppression, comparable to light quarks. In this exploratory study we investigate the energy loss of heavy quarks in high multiplicity proton proton collisions at LHC energies. We will find a small, however non-negligible energy loss of high momentum charm quarks.     

Classical microscopic description of U + U collisions

Calculations simulating head-on collisions between two mass-235 nuclei are made using classical kinematics, Monte-Carlo methods, and nucleon-nucleon cross sections. The calculated ratio of maximum particle density to the pre-collision nuclear density is ≈ 2 or 3, depending on details of the nucleon-nucleon scattering mechanism used.     

Baryon stopping in proton–nucleus collisions

We calculate the inclusive small-x valence quark production cross section in proton–nucleus collisions at high energies. The calculation is performed in the framework of the Color Glass Condensate formalism. We consider both the case when the valence quark originates inside the nucleus and the case when it originates inside the proton. We first calculate the cross section in the quasi-classical approximation resumming the multiple rescatterings with the nucleus. Then we include the effects of double logarithmic reggeon evolution and leading logarithmic gluon evolution in the obtained cross section. The calculated nuclear modification factor for the stopped baryons exhibits Cronin enhancement in the quasi-classical approximation and suppression at high energies/rapidities when quantum evolution corrections are included, providing a new observable which can be used to test Color Glass physics.     

Neutron and proton diffusion in heavy-ion collisions

A statistical theory for the exchange of protons and neutrons in heavy-ion collisions is formulated and applied to recent data. No systematic deviations are observed which could be evidence for (additional) quantal effects in the $\text{N}\text{Z}$ equilibration.     

Classical initial conditions in high energy nucleus-nucleus collisions

An iterative proceedure is proposed to compute the classical gauge field produced in the collision of two heavy nuclei. The leading order is obtained by linearizing the Yang-Mills equations in the light-cone gauge, and provides a simple formula for gluon production in nucleus-nucleus collisions. At this order k_t–factorization breaks down.     

Classical study of and collisions in intense laser fields

In this paper, ion-atom and ion-ion collisions in the presence of intense laser fields are qualitatively studied by Classical Trajectory Monte Carlo (CTMC) simulations. It is found that in contrast to the field-free collisions, the colliding ion and the target nucleus could absorb energy from the applied laser fields when the electrons escape from the collision system. This result is explained in terms of Coulomb explosion induced by the enhanced ionization at the so-called critical internuclear distance. Also, the corresponding energy gain cross-sections are evaluated. Received: 7 October 1998 / Received in final form: 28 January 1999     

Polarized proton collisions at 205 GeV at RHIC

The Brookhaven Relativistic Heavy Ion Collider (RHIC) has been providing collisions of polarized protons at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during acceleration from injection to 100 GeV. However, the intrinsic spin resonances beyond 100 GeV are about a factor of 2 stronger than those below 100 GeV making it important to examine the impact of these strong intrinsic spin resonances on polarization survival and the tolerance for vertical orbit distortions. Polarized protons were first accelerated to the record energy of 205 GeV in RHIC with a significant polarization measured at top energy in 2005. This Letter presents the results and discusses the sensitivity of the polarization survival to orbit distortions.     

Classical many-body model for heavy-ion collisions (II)

A four-parameter classical many-body model, specifically designed for heavy-ion collisions, is presented. Binding energies and densities of infinite and finite nuclei (N = Z) are satisfactorily reproduced. So also is the viscosity moment of the two-body scattering cross section at lab energies between 100 and 300 MeV.     

A microscopic calculation of fragment formation in nucleus-nucleus collisions

A microscopic model using effective and free nucleon-nucleon scattering cross sections is used to calculate the yields of projectile-like fragments from nucleus-nucleus collisions from 20 MeV/A to 2 GeV/A. Good agreement with reaction cross-section and fragment cross-section measurements is obtained. The enhanced yields of neutron-rich fragments observed experimentally at low beam energies from collisions of projectiles with heavy targets are reproduced somewhat better by the inclusion of a neutron-rich surface on the heavy-target nuclei. Each fragment mass is produced in a strongly localized region of the distance of closest approach between the colliding nuclei; lighter fragments come from small distances and the heavier ones from more peripheral collisions.     

Classical many-body model for heavy-ion collisions incorporating the Pauli principle

A classical model for heavy-ion collisions, introduced previously, has been extended to include certain effects of the Pauli principle. All nucleons are treated equally. They obey classical dynamics and interact through an ordinary two-body force and through a momentumdependent two-body “Pauli core” which satisfies, approximately, that $\text{p}{}_{\mathrm{ij}}\text{r}{}_{\mathrm{ij}}\text{≧ξ}\text{h}\text{?}$, where ξ is a dimensionless constant. A form for the Pauli core is presented. The ordinary two-body force has been adjusted to fit bulk properties of nuclei and to reproduce that moment of nucleon nucleon scattering cross sections which is relevant to hydrodynamics. The parameters of the forces are given.     

Polarization effects in ethylene molecule spectrum calculation

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 56, No. 3, pp. 482–486, March, 1992.