Processes In Heavy-ion Collisions Research Articles

Semiclassical theory of direct and deep inelastic heavy ion collisions

A sufficiently simple approach is formulated for the quantitative description of direct and multi-step processes in heavy ion collisions with arbitrary (not only small) mass, energy, and angular momentum transfer. The simplification is achieved owing to the use of semiclassical description of the colliding particles relative motion. The semiclassical approximation is used for the three-dimensional (not partial) distorted waves with accounting of all caustic properties, and the channel coupling is simulated by the dissipative forces. The transition amplitude is reduced to the one-dimensional integral along the so-called “transition lines” where the inelastic process is localized. The comparison is done with the experimental data and with exact calculations of some direct reaction cross sections. Heavy-ion-induced multi-step (quasidirect) massive transfer processes with the fast light particle formation are analyzed.

Dynamical features of medium energy heavy ion collision processes

A semiclassical dynamical simulation for medium and highenergy heavy ion collisions is presented and used to discuss in detail the features of evolution for 12C(25GeV; b = 0.0fm)+63 Cu reaction. From the calculated results it is shown that the model proposed can give a reasonable picture of the compression, expansion and fragmentation processes of the system in heavy ion reaction.

Photo‐ and Electro‐Production of a New Light Boson

AbstractIn GSI experiments, a light pseudoscalar boson of mass Φ 1.6 MeV may have been observed. In order to examine this possibility from a different aspect we propose to study the photo‐and electro‐production process of Φ‐particles. We calculate the cross section of neutral and charged Φ‐particles. We examine the possible role of these production mechanisms in the heavy ion collision processes.

Semiclassical description of multipair transfer processes in heavy ion collisions with superfluid systems

Pair transfer processes involving a superfluid system are studied in terms of phase space distributions constructed in a product representation which blends both ordinary- and gauge-space degrees of freedom. The time evolution of these distributions is followed by solving a collection of classical equations of motion, the quantal fluctuations being accounted for by the sampling of all possible initial orientations of the (undetermined) intrinsic system in gauge space. The excitation of the pairing rotational degree of freedom — corresponding to a variation in the number of particles — is induced by a gauge-deformed ion-ion potential, as befits the superfluid character of the target. Different orientations leading to the same final mass transfer may produce (in the case of large pairing deformation) interference effects in the final population of the members of the pairing rotational band. We also discuss how this approach can be used to describe the effect of pair transfer modes on sub-barrier fusion processes.

Correlations between transverse energy production and the Drell-Yan process in heavy ion collisions at high energy

The expression for the Drell-Yan cross section is presented which takes into account the geometry of heavy ion collisions. The Drell-Yan cross section is shown to be proportional to the transverse energy produced within a fixed rapidity interval. A dependence steeper than linear of the cross section for production of dileptons with masses larger than about 2 GeV on the transverse energy in a given rapidity bin would be a clear-cut signal for the formation of the quark-gluon plasma.

Correlation between neutrons and protons in heavy ion collisions

Generalized relationships between the variances of isobaric and isotopic distributions and the inclusive charge and mass distributions are deduced for isospin correlated statistical reaction processes in heavy ion collisions. We further deduce a general relation between the ratio of the inclusive mass to charge variances and the isospin correlation coefficient. In the context of the nucleon exchange model, the theoretical predictions agree with the experimental data in most of the cases.

Inelastic scattering of 16O from 60Ni at 114 MeV

The 60Ni( 16O, 16O') reaction has been measured with about 100 keV energy resolution at a bombarding energy of 114 MeV. Twelve transitions to 2 +, 3 −, 4 + and 5 − states were observed in the region below 5.8 MeV excitation and angular distributions of the corresponding differential cross sections were measured. DWBA and CC analyses are presented and spectroscopic information, in particular pertaining to the two-phonon strengths, is deduced. The deformation lengths β L R 2 are compared to previous results from inelastic scattering with 4He, 14C, and 16O particles. Supplementary data in the region of the giant quadrupole resonance (GQR) were obtained, although the GQR was not identified. The experimental results are used in a discussion of the energy loss process in heavy ion collisions.

Direct processes in heavy ion collisions at E ⩽ 20 MeV/u

Elastic and inelastic scattering at projectile energies of E ≃ 20 MeV/u have been studied using a magnetic spectrometer. It is shown that nuclear rainbow scattering for 12C + 12C allows to extract information from small inter nuclear distances. The role of the collective inelastic excitations is studied and it is shown that they lead to a decomposition of the projectile (or target)if the threshold for particle emission is close to the excitation energy of low lying collective states. The origin of the continuous background in the study of high lying excitations in nuclei is studied and it is shown that it can be analysed quantitatively.

Two-Dimensional Random Walk Process in Heavy Ion Collisions

Two-dimensional random walk model is applied to describe the interrelation between the energy loss and the mass transfer in heavy ion collisions. To take account of the energy loss associated with the mass transfer, we introduce the diagonal steps to the ordinary two-dimen­ sional random walk process. The average of the total kinetic energy loss Eo, as a function of the mass fragmentation, has a minimum at the initial mass fragmentation for the interaction time not very much exceeding the relaxation time. The results obtained from the present model are compared with some experimental data. They are in fairly good agreement with the experimental ones. The optimum values of the fractional energy or the distances of the neighboring sites LYE, are ~ 10 MeV for the 16 0(88 MeV) +27 Al reaction and ~ 24 Me V for the Ar(388 MeV)+' 32 Th reaction. These values of LYE are not contradictory to the assumptions inherent in the present model. We see that the smaller the magnitude of the step is, the less prominent the minima of the Eo as functions of the mass of the reaction products are. In the limit of the infinitesimal steps, i.e., the Fokker-Planck version, the minima disappear. So, in the context of the present model, the finite magnitude of the steps of the walker is suggested, together with the existence of diagonal steps.

Molecular model of the K-shell vacancy sharing process in heavy ion collisions

The one-electron model of the K-vacancy sharing process in heavy ion collisions is studied using a variation-perturbation scheme. The radial couplings are calculated analytically with the method of Macias and Riera. The validity of the Demkov-Meyerhof model is discussed and compared with numerical determinations of the transition probabilities.