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.     

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.     

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.     

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.     

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     

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.     

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     

Quantitative assessment of target dependence of pion fluctuation in hadronic interactions – estimation through erraticity

Event-to-event fluctuation pattern of pions produced by proton and pion beams is studied in terms of the newly defined erraticity measures χ(p, q), $\chi_q^{\prime}$ and $\mu_q^{\prime}$ proposed by Cao and Hwa. The analysis reveals the erratic behaviour of the produced pions signifying the chaotic multiparticle production in high-energy hadron–nucleus interactions (π ^???–AgBr interactions at 350 GeV/c and p–AgBr interactions at 400 GeV/c). However, the chaoticity does not depend on whether the projectile is proton or pion. The results are compared with the results of the VENUS-generated data for the above interactions which suggests that VENUS event generator is unable to reproduce the event-to-event fluctuations of spatial patterns of final states. A comparative study of p–AgBr interactions and p–p collisions at 400 GeV/c from NA27, with the help of a quantitative parameter for the assessment of pion fluctuation, indicates conclusively that particle production process is more chaotic for hadron–nucleus interactions than for hadron–hadron interactions.     

Azimuthal correlation and fractal study of compound hadrons (pions and protons) at Dubna and SPS energy

This paper presents an investigation of compound hadrons (pions and protons) distribution emitted from ²⁴Mg-AgBr and ¹²C-AgBr interactions both at 4.5 AGeV and ³²S-AgBr interactions at 200 AGeV. The study includes azimuthal correlations (two particle and three particle), azimuthal asymmetry and fractal behaviour. This paper reveals some interesting results.     

Spectra,elliptic flow and azimuthally sensitive HBT radii from the Buda-Lund model for $ \sqrt{{s_{NN}}}$ = 200 GeV Au + Au collisions

We present calculations of elliptic flow and azimuthal dependence of correlation radii in the ellipsoidally symmetric generalization of the Buda-Lund hydrodynamic model of hadron production in high-energy nuclear collisions. We compare them to data from RHIC by simultaneous fits to azimuthally integrated invariant spectra of pions, kaons and protons-antiprotons measured by PHENIX in Au + Au reactions at center-of-mass energy of 200 AGeV. STAR data were used for azimuthally sensitive two-particle correlation function radii and for the transverse momentum dependence of the elliptic flow parameter v ₂. We have found that the transverse flow is faster in the reaction plane than out of plane, which results in a reaction zone that gets slightly more elongated in-plane than out of plane. The model parameters extracted from the fits are shown and discussed.     

Two-dimensional multiplicity fluctuation analysis of target residues in nuclear collisions

Multiplicity fluctuation of the target residues emitted in the interactions in a wide range of projectile energies from 500 A MeV to 60 A GeV is investigated in the framework of two-dimensional scaled factorial moment methodology.The evidence of non-statistical multiplicity fluctuation is found in 16 O-AgBr collisions at 60 A GeV,but not in 56 Fe-AgBr collisions at 500 A MeV,84 Kr-AgBr collisions at 1.7 A GeV,16 O-AgBr collisions at 3.7 A GeV and 197 Au-AgBr collisions at 10.7 A GeV.     

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.     

The two-dimensional one-component plasma at Γ=2: The semiperiodic strip

The one-component two-dimensional plasma is studied in a strip of finite width, replicated periodically parallel to the long axis of the strip. Exact results for the one- and two-particle distribution functions are found at coupling =q ²/kT =2. The system is inhomogeneous: the one- and two-particle distribution functions show long-range order.     

Two-particle rapidity correlations in proton-nucleus interactions at 300 GeV

The single- and two-particle inclusive rapidity distributions for proton-nucleus interactions at 300 GeV in nuclear emulsions are presented. The analysis of the data with the two-particle rapidity correlation function R(ν₁, ν₂) shows clear evidence of short range correlations. A remarkable asymmetry between projectile and target hemisphere is found.     

The ridge as a shadowing effect in hydrodynamics

The aim of this work is to clarify the origin of the in-plane/out-of-plane effect, in the two-particle correlation function, computed with the NexSPheRIO code, in Au + Au collisions at 200 AGeV. We show that such an effect can be understood in terms of the shadowing effect caused by a peripheral high-energydensity tube.     

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     

Multiplicities of forward-backward particles in16O-emulsion interactions at 4.5 AGeV/c

An exclusive study of the characteristics of interactions accompanied by backward emission (θlab≥ 90°) of shower and grey particles in collisions of a 4.5 AGeV/c 16O beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward (θlab<90°) and backward hemispheres due to the interactions with the two emulsion components (CNO, AgBr) are presented and analyzed. The correlations between the different emitted particles are also investigated. The results indicate that there are signatures for a collective mechanism, which plays a role in the production of particles in the backward hemisphere. Hence, the backward multiplicity distribution of the emitted shower and grey particles at 4.5 AGeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favor the idea that the backward particles were emitted due to the decay of the system in the latter stages of the reactions.     

Two-particle correlation function and dihadron correlation approach

It is shown that, in the case of asymmetric nuclear interactions, the application of the traditional dihadron correlation approach to determining a two-particle correlation function C may lead to a form distorted in relation to the canonical pair correlation function _C². This result was obtained both by means of exact analytic calculations of correlation functions within a simple string model for proton–nucleus and deuteron–nucleus collisions and by means of Monte Carlo simulations based on employing the HIJING event generator. It is also shown that the method based on studying multiplicity correlations in two narrow observation windows separated in rapidity makes it possible to determine correctly the canonical pair correlation function C₂ for all cases, including the case where the rapidity distribution of product particles is not uniform.     

Multi-Boson correlations and classical transport models

We add the multi-particle Bose-Einstein correlations to classical simulations of ultra-relativistic heavy-ion collisions and calculate their influence on various observables such as multiplicity distributions, single-particle spectra and two-particle correlation functions. We demonstrate the method using simulations of ultra-relativistic heavy-ion collisions within a parton-string model for different systems of colliding nuclei at initial energy 200 AGeV.