Fragmentation and multifragmentation of 10.6A GeV gold nuclei

The experimental data on the interactions of 10.6A GeV gold nuclei in nuclear emulsions are analyzed with particular emphasis of target separation interactions and study of critical exponents. Charged fragment moments, conditional moments as well as two and three – body asymmetries of the fast moving projectile particles are determined in terms of the total charge remaining bound in the multiply charged projectile fragments. Some differences in the average yields of helium nuclei and heavier fragments are observed, which may be attributed to a target effect. However, two and three-body asymmetries and conditional moments indicate that the breakup mechanism of the projectile seems to be independent of target mass. We looked for evidence of critical point observable in finite nuclei by study the resulting charged fragments distributions. We have obtained the values for the critical exponents γ, β and τ and compare our results with those at lower energy experiment (1.0A GeV data). The values suggest that a phase transition like behavior, is observed. Received: 2 July 1998 / Revised version: 26 March 1999     

Features on Very Peripheral Collisions of ~(16)O-Em at 3.7 A GeV

From 1540 inelastic interactions of 3.7 A GeV~(16)O projectile with emulsion nuclei, we select samples of 87 and61 events carefully due to interactions of neutron(n) and singly charged particles(Z = 1), respectively. New results concerning the topology of such events are investigated. The average multiplicities of secondary relativistic particles that appear as shower tracks for n and Z = 1 stay more or less constant when compared with analogous data on p-Em at similar energy. The multiplicity distributions and the average values of the various secondary charged particles are studied and compared with the corresponding predictions by the cascade evaporation model.The results assume that the n or Z = 1 from~(16)O collide peripherally with an emulsion target and are considered as an expansion to the N-N collisions.     

Yields of projectile fragments in sulphur-emulsion interactions at 3.7 A GeV

This work presents the basic characteristics of singly,doubly and heavily charged projectile fragments(PFs) emitted in inelastic interactions of ~(32)S ions with photo-emulsion nuclei at Dubna energy(3.7 A GeV).Our experimental data are compared with the corresponding data for other projectiles at the same incident energy.The study of mean multiplicities of different charged PFs against the projectile mass shows a power-law relationship.The multiplicity distributions of singly and doubly charged PFs have been fitted well with a Gaussian distribution function.The yields of PFs broken up from the interactions of ~(32)S projectile nuclei with different target nuclei are studied.The beam energy dependence in terms of the various order moments is studied as well.     

Characteristics of alpha projectile fragments emission in interaction of nuclei with emulsion

The properties of the relativistic alpha fragments produced in interactions of ⁸⁴Kr at around 1 A GeV in nuclear emulsion are investigated. The experimental results are compared with the similar results obtained from various projectiles with emulsion interactions at different energies. The total, partial nuclear cross-sections and production rates of alpha fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass number and initial energy of the incident projectile nucleus are investigated. The yields of multiple alpha fragments emitted from the interactions of projectile nuclei with the nuclei of light, medium and heavy target groups of emulsion-detector are discussed and they indicate that the projectile-breakup mechanism seems to be free from the target mass number. It is found that the multiplicity distributions of alpha fragments are well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The mean multiplicities of the freshly produced or newly created charged secondary particles, normally known as shower and secondary particles associated with target in the events where the emission of alpha fragments were accompanied by heavy projectile fragments having Z ≥ 3 seem to be constant as the alpha fragments multiplicity increases, and exhibit a behavior independent of the alpha fragments multiplicity.     

Structures and angular distributions of slow and relativistic charged particles produced in 7Li-emulsion interactions at 3 GeV/c per projectile nucleon

Experimental results on the multiplicity distributions of various particles produced in the interactions of ⁷Li with emulsion nuclei at a momentum of 3 GeV/c per projectile nucleon are reported. A comparison with data on collisions induced by other nuclei at a nearly identical momentum per nucleon is presented in order to reveal the dependence on the projectile mass. The internal structure of ⁷Li is explored by studying the projectile fragment. The mean multiplicity of shower particles, 〈n _s〉, induced by ⁷Li is found to be less than that in the case of ⁶Li projectiles. The angular distributions of target fragments and relativistic charged secondaries are investigated. No shock-wave phenomena are observed. Forward-to-backward ratios are calculated for each case. The probability distributions for relativistic secondaries produced per unit rapidity are studied in detail, along with the rapidity densities and their dependence on the projectile and the target mass. A comparison of the angular spectra of shower particles produced in central and peripheral collisions supports the limiting-fragmentation hypothesis. The collisions in question seem to become more central with increasing shower-particle multiplicity.     

Features of the total disintegration events of heavyemulsion targets caused by 4.5A GeV/c16O

Total disintegration events produced by 4.5\,A GeV/c $^{16}$O--AgBr interactions are analysed to investigate the characteristics of secondary charged particles produced in such collisions. The multiplicity distributions of grey, black, and relativistic charged particles can be well represented by Gaussian distribution. The average multiplicity of grey particles is found to increase with the mass of projectile increasing, while that of black particles is found to decrease with the mass of projectile increasing. This result is in good agreement with the prediction of fireball model. Finally, the linear dependence between grey and black particles is observed, but there is no distinct dependence between the production of relativistic charged particles and the target excitation.     

Charged particle production in proton-, deuteron-, oxygen- and sulphur-nucleus collisions at 200 GeV per nucleon

The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton–nucleus and deuteron–gold interactions, as well as central oxygen–gold and sulphur–nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus–nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with ‘temperatures’ between MeV (p+S interactions) and MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions. Received: 28 October 1997 / Published online: 10 March 1998     

Interactions of 10.6 GeV/nucleon gold nuclei in nuclear emulsion

Stacks of nuclear emulsion were exposed at the Brookhaven AGS to a 10.6 GeV/n beam of gold nuclei in the BNL 868 experiment. A preliminary analysis of the main features of the interactions of these nuclei is reported here and compared with those observed previously at lower energies,E<1 GeV/n. The multiplicity and pseudo-rapidity distributions of the singly charged particles emitted both in central and in minimum bias samples of interactions have been analyzed in order to look for any non random effects indicative of the nuclear state during the interactions. The fragmentation characteristics of the gold projectiles appear to be different at 10.6 GeV/n from those at ≦1 GeV/n incident energy. Fission of the gold projectiles, which was relatively frequent at low energy, is almost entirely suppressed. Some of alpha particles from the projectile are emitted with very large transverse momenta. In gold-emulsion interactions the residual target nuclei are significantly smaller than in oxygen and sulfur interactions in emulsion.

     

Flow effects in high-energy nucleus collisions with Ag(Br) in emulsion

Various flow phenomena observed by a unique emulsion method are reviewed. The experimental data of the emission of projectile and target fragments and relativistic particles in collisions of 1–160 A GeV/c ¹⁶O, ²²Ne, ²⁸Si, ³²S, ⁸⁴Kr, ¹⁹⁷Au, and ²⁰⁸Pb nuclei with ¹⁰⁸Ag (⁸⁰Br) targets are investigated. The transverse-momentum approach, the flow-angle analysis using principal vectors, the azimuthal correlation functions, the method of azimuthal correlations between charged secondaries, and the method of Fourier expansion of the azimuthal angle distributions are applied. Evidence of the directed flow of spectators has been obtained in the medium-impact nuclear interactions. In azimuthal distributions, with respect to the reaction plane, the signal of the elliptic flow of participants has been observed.     

Nuclear fragmentation degree in the production of light projectile fragments

The projectile-target multiplicity correlations at the lowest (3.7 A GeV) and highest (200 A GeV) available energies in Sulfur-emulsion interactions are investigated in the framework of the participant-spectator model. We examined the light projectile spectator (singly, N_z=1 and doubly, N_z=2 charged projectile fragments). The measured average multiplicities of N_z=1 and N_z=2 at both incident energies showed a decrease with increasing the fragment charge, as well as the average values within experimental errors showed independence on the incident energy. The multiplicity measurements of different emitted secondary charged particles (produced particles, shower tracks, and target fragments, gray and black tracks) in the interactions of ³²S-Em at 3.7 A and 200 A GeV were carried out. However, the correlation between the mean multiplicities of secondary charged particles and both of the singly and doubly charged projectile fragments were investigated to shed some light on the interface of spectator and participant regions, and on the possible influences of the phenomena from the two regions on the collision dynamics.     

Fast helium production in interactions of 3.7 A GeV <Superscript>24</Superscript>Mg with emulsion nuclei

We have studied the properties of the relativistic helium fragments emitted from the projectile in the interactions of ²⁴Mg ions accelerated at an energy of 3.7 A GeV with emulsion nuclei. The total, partial nuclear cross-sections and production rates of helium fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass and energy of the incident projectile nucleus are investigated. The yields of multiple helium projectile fragments disrupted from the interactions of ²⁴Mg projectile nuclei with hydrogen H, light CNO and heavy AgBr groups of target emulsion nuclei are discussed and they indicate that the breakup mechanism of the projectile seems to be independent of the target mass. Limiting fragmentation behavior of fast-moving helium fragments is observed in both the projectile and target nuclei. The multiplicity distributions of helium projectile fragments emitted in the interactions of ²⁴Mg projectile nuclei with the different target nuclei of the emulsion are well described by the KNO scaling presentation. The mean multiplicities of the different charged secondary particles, normally defined shower, grey and black ( n_s, n_g and n_b) emitted in the interactions of 3.7 A GeV ²⁴Mg with the different groups of emulsion nuclei at different ranges of projectile fragments are decreasing when the number of He fragments stripped from projectile increases. These values of n_i ( i = s, g, b and h particles) in the events where the emission of fast helium fragments were accompanied by heavy fragments having Z 3 seem to be constant as the He multiplicity increases, and exhibit a behavior independent of the He multiplicity.     

Central events in the interactions of 28Si and 32S with heavy emulsion targets

Data on the multiplicity of secondaries in central events of ²⁸Si (14.6 AGeV) and ³²S (3.7 AGeV) interactions with AgBr emulsion nuclei have been compiled and studied. The dependence of the multiplicities of the outgoing charged stripping particles on the number of interacting nucleons and therefore on the impact parameter, as indicated by the target size, and consequently, on the degree of centrality is investigated. The resultant multiplicity distribution of the produced pions for each studied case is fitted by both Negative Binomial (NB) and Poisson distributions. The NB distribution is valid for most of the considered cases. The transparency of the target for a projectile was found to become more pronounced as the incident energy increased. Received: 20 June 2000 / Accepted: 17 January 2001     

Nuclear surface,mean field and isospin effects in Boltzmann master equation theory of pre-equilibrium reactions

Pre-equilibrium emission of nucleons and light charged particles is investigated in central collisions leading to the complete fusion of two heavy ions, within the Boltzmann master equation approach. Realistic nucleon momentum density distributions for both projectile and target nuclei are used and mean field effects are schematically introduced in the early stage of the reaction process. The isospin dependence of the calculation parameters is also discussed. Theoretical predictions of the spectra of the particles emitted both in symmetric and asymmetric interactions at incident energies of a few ten MeV/nucleon are in satisfactory agreement with the experimental findings.     

Heavy ion reactions at 75–100 MeV/nucleon

Energy and momentum component distributions of singly and doubly charged particles in¹⁶O-emulsion nucleus interactions at 75–100 MeV/n are presented. The parallel momentum distributions show larger shifts than at 2 GeV/n, indicating emission from systems with mean velocities ≈0.06 c relative to the parent nuclei. Particles with intermediate rapidities have, on the average, larger transverse momenta than particles with large rapidities. The charged particle multiplicity in peripheral collisions is the same at 0.1, 0.2 and 2 GeV/n, while the difference in multiplicity for central collisions is pronounced.     

The multiple scattering model analysis of high energy multiparticle production on emulsion nuclei

Data on multiparticle production on emulsion nuclei in the range 50–400 GeV/c have been analyzed in the framework of multiple scattering model developed by Capella and Krzywicki. It is shown that under some reasonable assumptions multiple scattering type models qualitatively reproduce multiplicity distributions of relativistic charged particles, one-particle spectra and two-particle inclusive correlations. When considering one-particle distributions a particular attention was given to the regions of small and large pseudorapidities. In the first region we found an apparent evidence for low-energy cascading, contribution and main features of which have been discussed. It is also discussed how strongly the behaviour of one-particle spectra at large rapidities would depend on the internal structure of a projectile particle.     

Multiplicity of secondary particles and fragmentation in nuclear interactions of22Ne and32S nuclei with emulsion at (4.1–4.5)A GeV/c

The interactions of 4.1AGeV/c ²²Ne and 4.5AGeV/c ³²S nuclei with emulsion have been studied and the dependence of the average multiplicities of the emitted secondary charged particles and the interacting projectile nucleons on the impact parameters have been investigated. The behavior of the Koba-Neilsen-Olesen (KNO) scaling formula of the multiplicity distributions produced due to the interactions of²²Ne and³²S at the energies mentioned above is satisfied by all target protons. The multiplicity distributions of the emitted⁴He fragments and the fragmentation cross-section relative to the inelastic cross-section have been investigated and give a⁴He-fragments yield which is always ten times greater than the yield of any other fragments. The dependence of the normalized mean multiplicity and the reduced multiplicity on the mass of the projectile and target nucleus can be described by a power law.     

Central collisions of24Mg nuclei with heavy emulsion group of nuclei (Br,Ag) at 4.5 AGeV/c momentum

Central collisions of²⁴Mg nuclei with the heavy (AgBr) group of emulsion nuclei are selected and analysed according to several selecting criteria. Theoretical calculations concerning cross sections for central events, average number of interacting protons from both projectile and target nuclei, multiplicity distributions of shower particles and dispersions, all based on the Glauber model, are performed to evaluate various criteria to select central events. The selection criterion based on the high multiplicity of total charged particles provides satisfactory agreement with the theoretical calculations.     

Coherent inelastic interactions of π+ and K+-mesons on Al and Au nuclei at 250 GeV/c

Cross-sections are obtained for coherent interactions of π⁺ and K⁺-mesons with Al and Au nuclei at 250 GeV/c, leading to three, five and seven charged mesons. The total coherent cross-section is (4.3 ± 0.5)% of the inelastic cross-section for each of the four meson-nucleus interactions. In 85% of the coherent events, the charged meson production is accompanied by neutral mesons. Effective mass distributions are presented for coherently produced particles, including charged mesons and photons, carrying total measured energy of more than 85% of the initial energy. Charged particle and γ spectra are analysed. No charge asymmetry is observed within the coherently produced cluster.     

Fragmentation of ^16O nuclei in nuclear emulsion

We present the topology of 16O fragmentation at 60A GeV in reactions with emulsion nuclei.We discuss the multiplicity distributions of projectile fragments.charged secondaries and their dependence on the target residues.     

PSEUDORAPIDITY DISTRIBUTIONS OF RELATIVISTIC SINGLY CHARGED PARTICLES IN HIGH ENERGY NUCLEUS-NUCLEUS COLLISIONS

The pseudorapidity distributions of relativistic singly charged part icles produced in high energy nucleus-nucleus collisions are described by the thermalized cylinder picture. The calculated results are in agreement with the recent experimental data of gold induced interactions at the Brookhaven National Laboratory.