Strong signal of dynamical long-range correlation among target fragments in relativistic and ultra-relativistic nuclear interactions

This paper reports an investigation on the two-particle long-range angular correlation among the target fragments produced in ²⁸Si–AgBr interactions at 14.5 AGeV, ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV. The experimental data have been compared with Monte Carlo simulated events to extract dynamical correlation. The data exhibit two-particle long-range correlation in emission angle space at all energies.     

Rapidity dependence of multiplicity fluctuations and correlations in high-energy nucleus–nucleus interactions

The multiplicity fluctuations of the produced pions were studied using scaled variance method in ¹⁶O–AgBr interactions at 2.1 AGeV, ²⁴Mg–AgBr interactions at 4.5 AGeV, ¹²C–AgBr interactions at 4.5 AGeV, ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV at two different binning conditions. In the first binning condition, the rapidity interval was varied in steps of one centring about the central rapidity until it reached 14. In the second case, the rapidity interval was increased in steps of 1.6 up to 14.4. Multiplicity distributions and their scaled variances were presented as a function of the dependence on the rapidity width for both the binning conditions. Multiplicity fluctuations were found to increase with the increase of rapidity interval and later found to saturate at larger rapidity window for all the interactions and in both the binning conditions. Multiplicity fluctuations were found to increase with the energy of the projectile beam. The values of the scaled variances were found to be greater than one in all the cases in both the binning conditions indicating the presence of correlation during the multiparticle production process in high-energy nucleus–nucleus interactions. Experimental results were compared with the results obtained from the Monte Carlo simulated events for all the interactions. The Monte Carlo simulated data showed very small values of scaled variance suggesting very small fluctuations for the simulated events. Experimental results obtained from ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV were compared with the events generated by Lund Monte Carlo code (FRITIOF model). FRITIOF model failed to explain the multiplicity fluctuations of pions emitted from ¹⁶O–AgBr interactions at 60 AGeV for both the binning conditions. However, the experimental data agreed well with the FRITIOF model for ³²S–AgBr interactions at 200 AGeV.     

Self-affine multiplicity fluctuation of target residues in relativistic nuclear collisions at a few GeV to a few hundred GeV

Self-affine multiplicity scaling is investigated in the framework of two-dimensional factorial moment methodology using the concept of the Hurst exponent (H). Our investigation on experimental data of the target-evaporated slow particles emitted in ³²S-AgBr interactions at 200 AGeV and ²⁸Si-AgBr interactions at 14.5 AGeV reveals that a better power law behavior is exhibited in self-affine analysis than self-similar analysis. This work shows a clear evidence of self-affine target fragmentation. Received: 22 October 2001 / Accepted: 6 March 2002     

Chaotic Multiparticle Production in Ring and Jet Structured Events in Heavy Ion Interaction: A Study in Multidimensional Phase Space

Two different classes of events exist in case of ¹⁶O–AgBr interactions at 60 AGeV, namely, ring-like and jet-like structured events. We have performed a rigorous study on the erratic behaviour of produced particles in ring-like and jet-like events in ¹⁶O–AgBr interactions at 60 AGeV with the help of entropy index μ_q. We have analysed the data in two dimensional phase space. The data reveal different pionisation for ring-like and jet-like events.     

Forward–backward multiplicity correlations in ring like and jet like events in <Superscript>16</Superscript>O–AgBr interactions at 60 AGeV

We have studied the forward–backward correlations of charged-particle multiplicities in symmetric bins in pseudorapidity space in order to gain insight into the underlying correlations structure of particle production in case of ring-like and jet-like events of ¹⁶O–AgBr interactions at 60 AGeV. The variance σ_c ² of a suitably defined the forward-backward asymmetry variable C has been determined. The experimental results confirm correlations of the produced particles in the forward and the backward pseudorapidity region for both ring-like and jet-like events.     

Production of charged pions, kaons and antikaons in relativistic C + C and C + Au collisions

Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(π⁺)/<A _part> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K⁺ multiplicities per participating nucleon M(K⁺)/ <A _part> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K^- multiplicity per participating nucleon M(K^-)/ <A _part> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K^-/K⁺ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected. Received: 10 December 1999 / Accepted: 14 November 2000     

Event-to-Event Fluctuation Analysis for Pions and Protons at SPS Energy

This study reports a detailed analysis of spatial fluctuations as well as event-to-event fluctuations of compound hadrons (pions + protons) produced in ³²S–AgBr interactions at 200 AGeV with a new technique known as erraticity analysis. This analysis is done for both emission-angle and azimuthal-angle phase spaces using gap-moment method. The study provides a strong evidence of erratic behavior of compound hadrons in ultra-relativistic nuclear collisions.     

Comment on “On the Anomalon Interpretation of 40Ar + Cu Collisions at 0.9 and 1.8 AGeV”

A recent article interpreted the experiment by Dersch et al. on the formation of ²⁴Na in ⁴⁰Ar + Cu interactions in a very simple manner. The results from emulsion experiments performed with 3.6 AGeV ²²Ne were adapted for the interpretation of the experiments with 1.8 AGeV ⁴⁰Ar. The model used the same mean value for the energy of minimum ionizing protons and pions at all angles. It is argued that a more complex approach is needed for a satisfactory interpretation.     

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     

Rotation-like behavior as a function of projectile energy and target mass

The azimuthal distributions produced in the intermediate energy⁴⁰Ar-induced reactions are calculated via the nuclear transport theory. The rotational collective motion is observed from the mid-rapidity particles emission. In addition to the investigation on particle emission in the coordinate space, the momentum distributions of emitted particles as a function of azimuthal angle are also discussed. The azimuthal distributions are fitted by performing Legendre polynomial expansion to second order. By incorporating the fluctuation between the estimated and true reaction plane into our calculations, quantitative agreements with the data are obtained for⁴⁰Ar+²⁷Al reactions below 85 MeV/nucleon. It is found that the rotation-like behavior becomes stronger with the increasing of the impact parameter and weaker with the increasing of the projectile energy. For⁴⁰Ar+²⁷Al system at about 85 MeV/nucleon the rotation-like behavior almost vanishes and the mid-rapidity azimuthal distribution tends to be isotropic. For 35 MeV/nucleon⁴⁰Ar-induced reactions the rotation-like behavior becomes weaker and the out-of-plane enhancement of particle emission appears with the increasing of target mass. The possible origins of these target mass dependent azimuthal distributions at mid-rapidity are discussed.     

Evidence of Multifractal Structure of Compound Multiplicity Distribution in 24Mg-AgBr Interactions at 4.5AGeV

This paper reports an analysis on fractality using the experimental data of compound multiplicity (pions + target protons) distribution in ²⁴Mg-AgBr interactions at 4.5 AGeV following the method proposed by F. Takagi. Takagi moments have been calculated for 2nd, 3rd, 4th, and 5th order in the emission angle and azimuthal angle space. The results of our study reveal the multi-fractal structure of compound multiplicity distribution.     

Application of BaF2 scintillator to off-line gamma-ray spectroscopy

Total cross sections of the monitoring reaction²⁷Al(d, 3p 2n)²⁴Na at 3·0 AGeV and 3·65 AGeV were determined from direct gamma-ray counting of irradiated targets with a spectrometer using a large volume BaF₂ scintillation crystal. Cross sections of 14·1 ± 1·3 mb and 14·7 ±± 1·2 mb are compared with previous data at other energies.     

Intra- and intergroup azimuthal correlations of particles in the interaction of gold nuclei with silver and bromine nuclei of track emulsions at the projectile energy of 10.6 GeV per nucleon

Inter- and intragroup azimuthal correlations of target and projectile fragments and of shower particles in the interactions between gold nuclei of energy 10.6 GeV per nucleon and silver and bromine nuclei of a track emulsion are studied at intermediate values of the impact parameter. The asymmetry index β′₁ and the collinearity index β′₂ of groups’ asymmetry vectors are used to study azimuthal correlations between two and three groups of particles. The interplay of effects of intra- and intergroup azimuthal particle correlations is investigated.     

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.     

Dielectron spectroscopy at 1-2 AGeV with HADES?

The HADES spectrometer at GSI (Darmstadt) is investigating the e ⁺ e ^- pair production in p+p, p+A and A+A collisions. In this contribution we would like to highlight the physics motivations and the experiments performed so far, focusing mainly on the first results coming from ¹²C + ¹²C collisions at 1 and 2AGeV, and on preliminary results from p+p/d+p collisions at 1.25AGeV. Original article based on material presented at HADRON 2007.     

Probing nuclear expansion dynamics with π−/π+-spectra

We study the dynamics of charged pions in the nuclear medium via the ratio of differential π^? - and π⁺-spectra in a coupled-channel BUU (CBUU) approach. The relative energy shift of the charged pions is found to correlate with the pion freeze-out time in nucleus-nucleus collisions as well as with the impact parameter of the heavy-ion reaction. Furthermore, the long-range Coulomb force provides valuable information on the expansion dynamics of the hot nuclear system. Detailed comparisons with experimental data for Au + Au at 1 AGeV and Ni + Ni at 2.0 AGeV are presented.     

Charge dependent effects in azimuthal two-particle correlations and cluster production

It is shown that neutral heavy cluster models provide a natural explanation of the recently observed charged dependent effects in azimuthal correlations between produced pions. This may be interpreted as evidence for identical particle effect and π⁺π^? resonance production in clusters.     

Abundance of Δ resonances in 58Ni + 58Ni collisions between 1 and 2 AGeV

Charged pion spectra measured in ⁵⁸Ni⁵⁸Ni collisions at 1.06, 1.45 and 1.93 AGeV are interpreted in terms of a thermal model including the decay of Δ resonances. The transverse momentum spectra of pions are well reproduced by adding the pions originating from the Δ -resonance decay to the component of thermal pions, deduced from the high transverse momentum part of the pion spectra. About 10 and 18% of the nucleons are excited to Δ states at freeze-out for beam energies of 1 and 2 AGeV, respectively.     

Ring-Like and Jet-Like Events in Ultra High-Energy Interactions—an Analysis in Terms of Multifractal Parameters

Ring-like and jet-like events produced in ¹⁶O-AgBr interactions at 60 AGeV are analyzed in terms of multifractal G-moment method and factorial moment method in both η space and ? space for emitted pions. Further, the Levy indices and multifractal specific heat c have been calculated. The results clearly indicate that μ and c both are different in ring-like and jet-like events depicting different mechanism in the production process.