Monte Carlo model for nuclear collisions from SPS to LHC energies

A Monte Carlo model to simulate nuclear collisions in the energy range going from SPS to LHC is presented. The model includes in its initial stage both soft and semihard components, which lead to the formation of color strings. Collectivity is taken into account considering the possibility of strings in color representations higher than triplet or antitriplet, by means of string fusion. String breaking leads to the production of secondaries. At this point, the model can be used as an initial condition for the further evolution by a transport model. In order to tune the parameters and see the results in nucleus–nucleus collisions, a naive model for rescattering of secondaries is introduced. Results of the model are compared with experimental data, and predictions for RHIC and LHC are shown. Received: 9 March 2001 / Published online: 21 September 2001     

Photoproduction of charged pions from deuterium at gamma-energies from 900 to 1,800 MeV and pion angles between 65 and 125°

The cross sections for production of pions, kaons, protons, antiprotons and deuterons at zero production angle have been measured in proton-nucleus collisions at 70 GeV in the momentum range of secondaries from 1.5 up to 3 GeV/c. Thin Al, Cu and W targets have been used in these measurements. The data onA-dependence of the production cross sections and particle yield ratios in momentum range from 1.35 up to 3.0 GeV/c are presented.     

Impact-parameter dependences of the number of interacting nucleons and mean multiplicities in heavy-ion collisions

The impact-parameter dependence of the mean number of interacting nucleons in high-energy heavy-ion collisions is considered in the case of identical atomic weights of colliding nuclei and in the case where one nucleus is much heavier than the other. It is shown that the use of a rare event—for example, an event of J/ψ or ? production—as a trigger may change significantly quantities representing the averages of the multiplicities for accompanying secondaries over impact-parameter values. The multiplicities of accompanying particles in central collisions can have but a slight dependence on the trigger. The observed multiplicity ratios for various secondaries in central and minimum-bias events can be used as a test in searches for quark-gluon plasma.     

New scaling law based on the hydrodynamical model of particle production

It is shown that Landau's hydrodynamical model of particle production accounts for many features of pion production in proton-proton collisions observed in recent experiments. A new energy-dependent scaling is proposed, in terms of which the distribution of secondaries at various energies falls on a universal curve having no adjustable parameters.     

Strange baryon production in heavy ion collisions

The rapidity distribution of Λ and ?Λ produced in nucleus-nucleus collisions at CERN energies is studied in the framework of an independent string model — with quark-antiquark as well as diquark-antidiquark pairs in the nucleon sea. It is shown that, besides the Λ-?Λ pair production resulting from the fragmentation of sea diquarks, final state interactions of co-moving secondaries π + N → K + Λ and ?N → K → ?Λ are needed in order to reproduce the data. Predictions for Pb-Pb collisions are presented.     

Scaling property of Φ,J/ψ and ϒ production bypp andp-nucleus collisions

The production of vector mesons ?,J/ψ and ? frompp collisions are investigated together with655-1 andK ⁰, assuming the same rest-frame for all secondaries, based on the Feynman-Yang scaling. It is found that the process behaves like the bremsstrahlung. No-free-parameters fits to the cross-sections are made with the normalization coefficients related to the quark contents of secondaries. Thep-nucleus production analyzed in terms of the optical model leads the same eikonal, characteristic of the absorption for ?,J/ψ and ?, independent of the energy.     

Midrapidity production of secondaries in pp collisions at RHIC and LHC energies in the quark–gluon string model

We consider the phenomenological implications of the assumption that baryons are systems of three quarks connected through a gluon string junction. The transfer of baryon number in rapidity space due to the string junction propagation is considered in detail. At high energies this process leads to a significant effect on the net baryon production in hN collisions at midrapidities. The numerical results for midrapidity inclusive densities of different secondaries in the framework of the quark–gluon string model are in reasonable agreement with the experimental data. One universal value, λ≃0.25, for the strangeness suppression parameter correctly describes the yield ratios of Λ/p, Ξ/Λ, and Ω/Ξ. The predictions for pp collisions at LHC energies are also presented. PACS 25.75.Dw     

Analysis of shower particle multiplicity in hadron-nucleus collisions in the few hundred GeV region

An analysis of relativistic charged secondaries produced in hadron-nucleus collisions in the few hundred GeV region is presented from the point of view of the structure of hadrons and to examine the possibility of discriminating different theoretical models. An attempt has been made to study the mean normalised multiplicity ratio in the central region and its dependence on the mean number of intranuclear collisionsv. The rate of increase in the production of particles exhibits good agreement with our proposed approach of the constituent supercluster model.     

Production of secondaries in high-energy <Emphasis Type="Italic">d</Emphasis>+Au collisions

In the framework of the quark–gluon string model we calculate the inclusive spectra of secondaries produced in d+Au collisions at intermediate (CERN SPS) and at much higher (RHIC) energies. The results of numerical calculations at intermediate energies are in reasonable agreement with the data. At RHIC energies numerically large inelastic screening corrections (percolation effects) should be accounted for in the calculations. We extract these effects from the existing experimental data of RHIC on minimum-bias and central d+Au collisions. The predictions for p+Au interactions at LHC energy are also given.     

Inclusive spectra of secondaries produced on nuclear targets at superhigh energies and with violation of Feynman scaling

Effects of Feynman scaling violation in yields of hadron secondaries inpA and πA collisions that arise when initial energy is increased are considered. There result from the growth of hadron-nucleon cross sections and an expected increase of the average transverse momenta of secondaries. The model of quark-gluon strings is used to calculate the inclusive spectra of secondaries. Interactions with a fixed number of nucleons are calculated, taking account of the growth of the slope parameter in elastichN scattering. Violation of Feynman scaling at superhigh energies turns out to be stronger than the additive quark model predicts it to be.     

Production of secondaries in high-energy heavy-ion collisions

In the framework of the quark-gluon string model, we calculate the inclusive spectra of secondaries produced in heavy-ion collisions at intermediate (CERN SPS) and at much higher (RHIC) energies. We demonstrate that the mechanism of secondary production changed drastically in the energy interval √s = 20–60 GeV and that it is in agreement with qualitative estimates of Glauber-Gribov theory. The results of numerical calculations at intermediate energies are in reasonable agreement with the data without change of the model parameters. At RHIC energies, numerically large inelastic screening correlations should be accounted for in calculations. The text was submitted by the authors in English.     

Azimuthal correlations of secondary particles in collisions between gold nuclei and track-emulsion nuclei at a gold-nucleus energy of 10.6 GeV per nucleon

Charged secondaries from collisions of gold nuclei with track-emulsion nuclei showed azimuthal correlations consisting in (i) the asymmetric emission of projectile and target fragments in opposite directions and (ii) an azimuthal quasicollinearity of shower particles in individual events. The measurement errors were investigated and taken into account. The experimental data in question can be interpreted within the model of Gaussian distributions of transverse momentum components.     

Centrality dependence of particle production at RHIC and the combinational approach

The newly proposed combinational approach, called the grand combination of models (GCM), as will be described in detail in the text, is still under our careful scrutiny. By applying it, we have attempted to analyze here the characteristics of both the transverse momentum ( )-, and centrality dependence of the production of the main varieties of the secondaries measured in AuAu collisions at BNL-RHIC at both GeV and GeV by PHENIX Collaboration. Besides, with the help of it, we have also investigated the nature of the centrality dependence of the average transverse momenta of the various major categories of particles in AuAu collisions at RHIC. The model seems to survive quite smoothly the acid tests of the latest PHENIX data, as it accommodates data modestly well on these twin aspects. The study reveals a kind of universality of nature of the hadronic secondaries and also of the basic particle and nuclear interactions at high energies. However, in the end, we precisely point out both the strengths and limitations of the specific model under consideration here.Received: 2 April 2003, Revised: 29 July 2003, Published online: 23 December 2003PACS: 13.60.Hb Total and inclusive cross-sections (including deep-inelastic processes) - 25.75.-q Relativistic heavy-ion collisions     

Second-order interference as a tool for the determination of hadron fireball dimensions

Correlations between identical particles emitted simultaneously in hadron collisions can be used to determine the dimensions of the region where the secondaries are produced. The method is similar to that used by radio-astronomers to measure the angular dimensions of sources.     

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.     

Production of secondaries in relativistic nuclei collisions at high energies

Using the multiple-scattering theory and quark-gluon string model, the averaged and central collisions between high-energy nuclei are studied. Production of light flavour hadrons as well as charmed and beauty mesons and baryons is considered. We present predictions for mean multiplicities of secondaries, inclusive spectra and distributions over multiplicity for the case of Au?Au collisions with energy 100 GeV per nucleon in every beam.     

New tangles in TeV physics: Outline and some comments

Summary Ultrahigh-energy physics experiment by JACEE collaboration reveals, on the one side, nature's strong favouritism to the production of photons compared to the charged particles as secondaries in heavy-ion collisions, whereas some other repeated measurements at cosmicray energy ranges by Pamir and Chacaltaya collaboration and by Brazil-Japan collaboration indicate—save the very recent null observation reported by China-Japan collaboration—the production of charged particles in large numbers without any accompanying photons called centauro or minicentauro events at high altitudes. No explanation for either of these two types of events has so far been successfully given for which it seems that, contrary to expectations, the TeV physics poses more questions than it actually answers. The latest results in the TeV region of energies, thus, only add further to confusion and do not seem to usher in an end to it.     

Structure of final states with a high transverse momentum π0 in proton-proton collisions

We present a study of the final state structure in proton-proton collisions (√s = 53 GeV) where a large transverse momentum π⁰ (p_t > 2 GeV/c) is produced at an angle of 90°. Charged secondaries have been detected and momentum analysed in the split field magnet detector at the CERN Intersecting Storage Rings. The large angular coverage of this detector extends over ±2.5 units of rapidity and ±30° of azimuth with respect to the trigger π⁰, both towards and away from it. In each of these directions, where we observe similar strong correlations, we present charged particle distributions, in rapidity and momentum. In the hemisphere containing the trigger π⁰ we have measured the cross section for inclusive production of large transverse momentum ?^± mesons. In the opposite hemisphere the data exhibit several features predicted by hard scattering quark-parton models: coplanarity and short-range rapidity correlation for the large transverse momentum secondaries as well as a transverse momentum sharing distribution similar to that observed in deep inelastic electro-production and in e⁺e^? collisions.