Intermittency in relativistic heavy-ion collisions

Corrected scaled-factorial-moments are calculated for the multiplicity distributions of shower particles in different phase spaces. An intermittency power-law is observed in the central collisions of³²S and¹⁶O at 200A GeV,¹⁶O at 60A GeV and²⁸Si at 14.5A GeV in nuclear emulsion.     

Systematic study of multiparticle production in nucleus–nucleus interactions at 14.6 A GeV

An experimental analysis of 855 events induced by 14.6 A GeV ²⁸Si in nuclear emulsion is presented. Mean multiplicities of charged secondary particles produced in the nuclear interactions are studied and compared with the results from the other experiments for the same projectile at 3.7 A GeV as well as data for proton at similar energy (14 GeV). An analysis of pseudorapidity densities of target fragments (black and grey particles) is also performed. The behaviour of the KNO scaling law of the multiplicity distribution for shower particles has been examined. In order to accumulate knowledge about the intermittent behaviour of shower particles, the scaled factorial moments (SFMs) are computed in η-space and ?-space for a set of data in the ²⁸Si–AgBr events. Furthermore, validity of limiting fragmentation of shower particles produced in central collision events induced by ²⁸Si-emulsion interactions has been tested. A crude estimation for the energy density of the nuclear matter formed in the central collision events at our energy has been examined.     

Intranuclear cascading at ultrahigh energy in heavy-ion interactions

Intranuclear cascading mechanism one of the important non-linear effects in high energy nucleusnucleus collisions is investigated. The data on multiplicity (n _s ) and pseudorapidity (η) distributions of shower particles produced by³²S and¹⁶O at 200A GeV,¹⁶O at 60A GeV,²⁸Si at 14.5A GeV and He at ≈140A GeV are presented and compared with the string model VENUS, which takes into account the cascade interactions of secondary particles. The effect of the intranuclear collisions on the distributions of <η> versus <n _s > is discussed for all the beams.     

Pseudorapidity distributions from pion-emulsion interactions in the energy range 60 GeV to 300 GeV

The analysis of experimental data for pion-nucleus interactions in the energy range 60 GeV–300 GeV is presented. The pseudorapidity distributions of shower particles are analyzed in terms of pion energy and the average number of intra-nuclear collisions of the projectile. The particle densities in the projectile fragmentation region are compared to predictions of the additive quark model. The relation between the average number of wounded quarks in the projectile and the number of fast protons emitted from the struck nucleus is derived and used to extract from the experimental π^?-emulsion data the fragmentation functions for both wounded and spectator quarks. These functions are then used to described the results of independent π^?-proton and π^?-deuteron experiments.     

Systematic study of projectile fragments in nucleus-nucleus collisions at 4.1-4.5 A GeV/c and multi-source thermal model

The multiplicity distributions of projectile fragments (PFs) produced in interactions of (⁴He, ¹²C, ¹⁶O, ²²Ne and ²⁸Si with emulsion (Em) at 4.1?C4.5 A GeV/c beam energies, and their dependence on target groups (H, CNO and AgBr) are presented and have been reproduced by using a multi-source thermal model. The dependence of the mean multiplicities on masses of projectile and target nuclei is investigated. The experimental results are compared with the corresponding ones from the theoretically calculated ones. The experimental results agree with theoretical calculations using the multi-source thermal model.     

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.     

Comparative study for nucleus-nucleus interactions and modified cascade evaporation model at (4.1 – 4.5) AGeV/c

The characteristics of the nucleus-nucleus collisions at high energy for the interactions of ¹H, ⁴He, ¹²C, ¹⁶O, ²²Ne, ²⁸Si and ³²S with emulsion at momentum (4.1 – 4.5) AGeV/c have been investigated. It has been found that the multiplicity distributions of the different emitted particles and their average values can be described by the modified cascade evaporation model. The model reproduces satisfactorily the multiplicity distributions of the shower, grey and black particles and the correlations between their multiplicities. It has been seen that the number of the produced shower particles increases with the increase of the projectile mass number. From the correlation between the average multiplicity of the evaporation particles and the number of the produced particles, it was found that a phase transition in the target system may occur. The calculated pseudo-rapidity distributions of the produced shower particles are typically Gaussian shaped in the mid-rapidity region and agree well with the experimental data. Also, the angular distributions of the grey and black particles have been investigated. The angular distributions of the grey particles show a universal shape independent of the type of projectile. The angular distributions of the black particles are nearly isotropic with a small asymmetry in the forward direction. The modified cascade evaporation model, reproduces the general characteristics of the nucleus-nucleus interactions and gives an explanation for the multiparticle production process.     

Fragmentation of target spectators in ultrarelativistic heavy ion collisions

We demonstrate that the assumption that target spectators fragment isotropically in a gently moving coordinate system is in agreement with pseudorapidity distributions, measured in central ultrarelativistic heavy ion collisions of projectile energy from 14.5A GeV to 200A GeV. Target spectator remnants might be excluded from measurement by introducing a low energy cutoff for the accepted particles at approximately 200 MeV. An approximate scaling is presented for the pseudorapidity distribution of the target spectator fragments. Theoretical tools used for studying intermediate energy heavy ion collisions seem to be applicable in describing target spectator fragmentation in ultrarelativistic heavy ion collisions.     

The percolation mechanism for fragmentation of nuclei using Monte Carlo technique

A statistical bond-percolation model for the fragmentation has been applied to the proton-induced reactions assuming a lattice structure to the prefragment nucleus and using the Monte Carlo technique to determine the bond to be broken. The model succeeded to reproduce the essential features of the mass yield curves for the p-Cu reaction at 3.9 GeV and to describe qualitatively the charge and the multiplicity distributions of the projectile fragments for the ²⁸Si interactions with the quasi-free emulsion nucleon at 3.7 AGeV.     

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.     

Factorial moments and short range correlation at relativistic energies

We present the results on cumulant moments obtained from horizontally and vertically averaged factorial moments for the shower particles, produced in³²S-emulsion at 200 A GeV,¹⁶O-emulsion at 200 A GeV,¹⁶O-emulsion at 60 A GeV,²⁸Si-emulsion at 14.5 A GeV and proton-emulsion at 800 GeV. Except the cumulants of order two, all other moments are consistent with zero within their statistical uncertainties. The strength of correlation length for each beam is higher than the previously observed values.     

Fragmentation in ^16 O-emulsion interactions at 3.7 A GeV

The topology of ¹⁶O fragmentation at 3.7 A GeV in reactions with emulsion nuclei is presented. The multiplicity distributions of projectile fragments,charged secondaries and their dependences on the projectile residues are discussed.     

Factorial Moments of 28 Si Induced Interactions with Ag(Br) Nuclei

Scaled factorial moment analysis for the multiplicity distribu- tions of shower particles in the pseudorapidity phase space has been done. An evidence for the presence of dynamical uctuations has been shown for the non-peripheral interactions of28Si+Ag(Br) at 14.6 A GeV/c and 4.5 A GeV/c.The results have been compared with the values obtained from data sample calculated by cascade-evaporation model.     

28Si(32S) fragmentation at 3.7 A, 14.6 A and 200 A GeV

The fragmentation topology of²⁸Si at 3.7A GeV and 14.6A GeV and³²S at 200A GeV in reactions with emulsion nuclei is presented. The fragmentation cross sections are very similar at all three energies. A statistical percolation model can qualitatively describe the data forZ 6. The He production is underestimated and the 3 Z 5 fragments overestimated by this model.     

Rapidity density fluctuations in 14.5A GeV/c 28Si-nucleus interactions

Results on correlation and clusterization amongst relativistic charged particles produced in 14.5A GeV/c ²⁸Si-nucleus collisions are presented by studying rapidity density distribution of relativistic charged particles in various pseudorapidity windows. These results are observed to agree reasonably well with the predictions of Lund Monte Carlo model FRITIOF.     

Multiplicity distributions of shower particles and target fragments in 7Li–Em collisions at 3 A GeV/c

Multiplicity distributions of shower particles and target fragments in ⁷Li–Em (emulsion) collisions at 3 A GeV/c are experimentally studied. In the framework of the multisource thermal model, the multicomponent Erlang distribution is used to describe the experimental multiplicity distributions of shower particles, grey fragments, black fragments, and heavily ionized fragments. The correlations between these multiplicities are experimentally reported. With the increase of impacting centrality (or the target fragment multiplicity), a saturation phenomenon for shower particle multiplicity is observed in the experiment.     

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.     

Justification of Landau Hydrodynamic-Tube model in central relativistic heavy-ion collisions

The statistical event-by-event analysis of inelastic interactions of ¹⁶O and ³²S nuclei in emulsion at 60 A?GeV/c and 200 A?GeV/c reveals the existence of groups of high multiplicity events belonging to very central nuclear interactions with Gaussian pseudorapidity distributions for produced particles as suggested by the original hydrodynamic-tube model. Characteristics of these events are presented. The experimental observations are interpreted as a result of quark-gluon plasma formation in the course of central nuclear interactions.     

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.     

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.