Relativistic Heavy Ion Reactions Research Articles

Target fragment energies and momenta in the reaction of 4.8 GeVC12and 5.0 GeVNe20withU238

Target fragment recoil properties were measured using the thick-target---thick-catcher technique for the interaction of 4.8 GeV $^{12}\mathrm{C}$ and 5.0 GeV $^{20}\mathrm{Ne}$ with $^{238}\mathrm{U}$. The target fragment energies and momenta are very similar for the reaction of 4.8 GeV (400 MeV/nucleon) $^{12}\mathrm{C}$ and 5.0 GeV (250 MeV/nucleon) $^{20}\mathrm{Ne}$ with $^{238}\mathrm{U}$. In the complex variation of fragment momenta with their $\frac{N}{Z}$ ratio, one finds evidence suggesting the existence of several mechanisms leading to the formation of the target fragments. Comparison of these results with the predictions of the intranuclear cascade model of Yariv and Fraenkel and the firestreak model shows that both model predictions grossly overestimate the target fragment momenta.[NUCLEAR REACTIONS $^{238}\mathrm{U}(^{12}\mathrm{C},x)$, $E=4.8$ GeV; $^{238}\mathrm{U}(^{20}\mathrm{Ne},x)$, $E=5.0$ GeV; measured target fragment recoil properties; deduced target fragment energies, momenta; relativistic heavy ion reactions; target fragmentation; spallation; fission; intranuclear cascade model; firestreak model; thick-target-thick-catcher technique; Ge(Li) gamma-ray spectroscopy.]

Approach to equilibrium in high energy heavy ion collisions

The time development of hadrochemical composition and momentum distribution in hot, dense hadronic matter formed in relativistic heavy ion reactions is investigated in the framework of a statistical model. Calculated chemical composition and inclusive spectra are compared with experimental data.

Direct fragmentation and hard-scattering processes in relativistic heavy-ion reactions

In a relativistic heavy-ion reaction, there are many processes which contribute to fragmentation phenomenon. Here we examine two: the direct fragmentation process in which the detected subsystem is emitted from a parent nucleus without additional scattering, and the hard-scattering process in which a subsystem from one nucleus makes a collision with a subsystem from the other nucleus. In terms of a combination of these two processes, the proton inclusive data of Anderson et al. for the reaction $\ensuremath{\alpha}+^{12}\mathrm{C}\ensuremath{\rightarrow}p+X$ at different bombarding energies can be successfully analyzed. We find that the direct fragmentation process dominates the cross section at 0\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{}. On the other hand, the hard-scattering process dominates the cross section at the quasi-elastic peak when the transverse momentum far exceeds 0.1 GeV/c. Our model leads naturally to a new scaling variable which is the generalization of the Feynman scaling variable for situations when the rest masses are not negligible. As the nuclear momentum distribution enters into the model in a very important way, our analysis constitutes in essence a semi-empirical determination of the nuclear momentum distribution. Furthermore, since a single nucleon can carry a large fraction of the momentum of the parent nucleus in a cooperative manner, relativistic heavy-ion reactions may be utilized to provide valuable information on the high momentum tail of the nuclear momentum distribution when the effects of final-state interactions are better understood.NUCLEAR REACTIONS Theoretical analysis of relativistic heavy-ion reactions. Direct fragmentation and hard-scattering processes. Applied to $\ensuremath{\alpha}(^{12}\mathrm{C}, px)$. Scaling variable. Nuclear momentum distribution and nuclear structure function.

Microscopic and Macroscopic Model Calculations of Relativistic Heavy-Ion Fragmentation Reactions

The possibility of observing previously postulated neutron-proton correlations in the nuclear ground state via relativistic heavy-ion reactions is examined. The isotope-production cross sections from the reaction of 213-MeV/nucleon $^{40}\mathrm{Ar}$ with $^{12}\mathrm{C}$ are calculated with a correlated abrasion-ablation model and with an uncorrelated intranuclear cascade model, and the results compared to recent experimental data. The neutron-proton correlations may only be visible in products near the mass of the fragmenting nucleus.

On the fragmentation of the projectile in relativistic heavy-ion collisions

The fragmentation of the projectile in relativistic heavy-ion reactions is usually described in terms of a two-step model called abrasion-ablation. The abrasion part is reformulated in the framework of the Boltzmann equation. The results are compared with other approaches and with experiment.

Charge multiplicity in relativistic heavy ion collisions: A statistical model approach

We use fireball geometry and a statistical model to calculate charged particle associated multiplicity in relativistic heavy ion reactions. General expressions for multiplicity distributions based upon this model are derived. The constraints of charge and baryon number conservation are shown to lead to modified Poisson distributions. The expressions developed are applicable to all nonstrange particles and composites. Comparison is made with existing data.

Abrasion-ablation calculations of large fragment yields from relativistic heavy ion reactions

Calculations of large mass fragment yields from high-energy heavy-ion reactions are performed based on the abrasion-ablation model. The geometrical picture of the clean-cut fireball model is used to calculate the number of participant nucleons in the abrasion stage and the excitation energy of the spectators (primary residues). A standard statistical evaporation code is used to calculate the ablation stage. Results from this model show an overall agreement with experimental data, although some systematic discrepancies are found and discussed. A frictional spectator interaction is introduced which increases the average excitation energy of primary fragments and improves the results considerably.NUCLEAR REACTIONS Relativistic Heavy-ions, abrasion-ablation model, peripheral reactions, calculated fragmentation cross sections.

Properties of participants and spectators in non-peripheral Fe-induced reactions at 1.7 A GeV

Central relativistic Fe-induced heavy ion reactions in emulsion have been isolated and we observe that a clean-cut thermal participant-spectator model fails in predicting the experimental angular distributions of charged particles.

Chemical equilibrium relations used in the fireball model of relativistic heavy ion reactions

The fireball model of relativistic heavy-ion collision uses chemical equilibrium relations to predict cross sections for particle and composite productions. These relations are examined in a canonical ensemble model where chemical equilibrium is not explicitly invoked.NUCLEAR REACTIONS Fireball; particle production; relativistic heavy ions; chemical equilibrium.

In-beam nuclear gamma-ray studies of relativistic heavy ion reactions

Abstract Discrete nuclear γ-rays following interactions of relativistic 12 C and α projectiles with Sr, Na, S and Ca targers were measured in-beam with Ge(Li) detectors. The observed γ-rays were due mostly to the first-excited-state-to-ground transitions of target fragments produced in peripheral collisions of the heavy ions. Characteristic features of the peripheral process consistent with the projectile-fragment studies were observed. The general behavior of the reactions was qualitatively understood with a picture of a fast-cascade followed by evaporation.

Target residue mass and charge distributions in relativistic heavy ion reactions

Calculations of the mass and charge distributions for the heavy target residues from relativistic heavy ion reactions are carried out for the reaction of $^{12}\mathrm{C}$ with $^{238}\mathrm{U}$, $^{208}\mathrm{Pb}$, $^{197}\mathrm{Au}$, Ag, and Cu and compared with experimental data. The primary product distributions are calculated using the abrasion-ablation model. Nuclear charge distributions are calculated using either a stochastic model or a model based upon the zero-point oscillations of the giant dipole resonance. Standard statistical deexcitation calculations are used to calculate secondary product distributions. The results show that some of the principal features of the residue mass and charge distributions can be accounted for with the simple assumptions of the abrasion-ablation model and the assumption that product charge distributions are due to the sudden nature of the interaction and the zero-point oscillations of the giant dipole resonance.NUCLEAR REACTIONS Calculated $\ensuremath{\sigma}(Z, A)$ for 25.2 GeV $^{12}\mathrm{C}$+$^{238}\mathrm{U}$, $^{208}\mathrm{Pb}$, $^{197}\mathrm{Au}$, Ag, and Cu; comparison with data, abrasion-ablation, giant dipole resonance, relativistic heavy ion reactions, target residue mass distribution, charge distribution.

Pion production in relativistic heavy-ion reactions

High-energy heavy-ion reaction data on pion production near ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{} \mathrm{and} 180\ifmmode^\circ\else\textdegree\fi{}$ are analyzed. The result strongly suggests that the forward (backward) pions are due to materialization of the kinetic energy of the effective projectiles (effective targets) in peripheral nucleus-nucleus collisions. A statistical interpretation for the observed energy distributions is discussed.

Further studies of large collision residues in relativistic heavy-ion reactions with heavy nuclei

Target residue mass and charge distributions have been measured radiochemically for the reaction of 25.2 GeV 12C ions with Au and Pb. Enhanced product yields for A = 140−170 are found that are not present in reactions of Pb with GeV protons. The shape of the mass distribution in this region is used to define a pre-equilibrium product mass distribution.