High-energy Hadron-nucleus Collisions Research Articles

The Fragmentation Region of High Energy Nucleus-Nucleus and Hadron-Nucleus Collisions

The fragmentation region of particles produced in high energy nuclear collisions provides a laboratory for studying high baryon number density systems. This talk outlines work in progress that attempts to compute properties of the matter produced in these collisions at the highest energies.

Statistical hadronization and multiplicities in high-energy hadron–nucleus collisions

Concepts from statistical mechanics and ensemble theory are applied to study the characteristic properties of charged particle production in hadron–nucleus collisions at high energy. In the present study we utilize the predictions from different approaches using statistical mechanics. The Tsallis q-statistics is used to study the regularity in multiplicity distributions in hadron–nucleus collisions at high energies as one of the interesting options. Gamma distributions and a possible microcanonical generalization of Tsallis distribution have also been exploited to describe the data.

On the mechanisms of cumulative-proton production in high-energy hadron-nucleus and nucleus-nucleus collisions

The importance of studying processes involving cumulative-proton production stems from their direct relation to the formation of multiquark configurations, so-called fluctons, in a nucleus owing to nucleondensity fluctuations in which two or more nucleons occur at a distance shorter than 1 fm from one another. According to [1], multiquark configurations may arise in two different physics patterns. The first, caused by a fluctuation of the target-nucleus density, is referred to as a cold model, while the second, associated with nuclear-matter compression occurring under the effect of an incident hadron or a projectile nucleus and leading to the formation of dense quark bags, is called a hot model. It should be noted that, in early interpretations, the production of cumulative protons was related to the Fermi momenta of nucleons. However, the calculations that took into account the Fermi momentum of nucleons [2] showed that the spectrum of fast ( p> 500 MeV/c) cumulative protons cannot be described in this way. In the present study, we examine new features of the process of cumulative-proton production—in particular, we analyze the behavior of the mean multiplicity of cumulative protons as a function of the charge and mass numbers of the target nucleus. Previously, our group studied [3–5] cumulativeproton production in π −12 С, pС, 4 НеС, СС, 16 Op, and p 20 Ne collisions at primary energies in the range 3–300 GeV and, on the basis of a vast statistical data sample, confirmed the universal regularity that the slope parameter of inclusive cross sections for cumulative protons in the cumulative number β is independent of the primary energy and mass of the incident particle or nucleus. It was shown that the fraction of events involving cumulative-proton production on a carbon nucleus is sensitive to the

On the possibility of describing the multiplicity distribution of protons in high-energy hadron-nucleus collisions within a three-step interaction model

On the possibility of describing the multiplicity distribution of protons in high-energy hadron-nucleus collisions within a three-step interaction model

On the production of cumulative protons in high-energy hadron-nucleus and nucleus-nucleus collisions

On the production of cumulative protons in high-energy hadron-nucleus and nucleus-nucleus collisions

Minijet transverse spectrum in high-energy hadron-nucleus collisions

Hadron-nucleus collisions at CERN LHC energies are studied by including explicitly semihard parton rescatterings in the collision dynamics. Under rather general conditions, we obtain explicit formulas for the semihard cross section and the inclusive minijet transverse spectrum. As an effect of the rescatterings the spectrum is lowered at small ${p}_{t}$ and is enhanced at relatively large transverse momenta, the deformation being more pronounced at increasing rapidity. Its study allows to test the proposed interaction mechanisms and represents an important baseline to examine nucleus-nucleus collisions.

AGK CUTTING RULES AND PERTURBATIVE QCD

The purpose of this article is to describe a few features of semihard interactions, in high energy nuclear collisions, that are better understood with the help of the AGK cutting rules, and of the probabilistic picture of the interaction which follows. In the first part of the article the cutting rules are discussed for the simplest component of the forward three-body parton amplitude in the large s fixed t limit. The case considered corresponds to the term — at the lowest order in the coupling constant and with vacuum quantum number exchange in both t channels — of the amplitude which describes the interaction of a high energy quark with the two target quarks. The different leading cuts of the amplitude are shown to be proportional to one another with the same weights of the cutting rules derived in the context of multi-Pomeron exchange. The probabilistic picture of the multiple interactions, which originates from the cutting rules, and the self-shadowing cross sections are then discussed. The second part of the article deals with the semihard interactions. The semihard cross section in high energy nucleus–nucleus collisions is represented as a self-shadowing cross section, and a feature which is pointed out is that the single scattering factorized expression of the perturbative QCD parton model holds at any order in the multiparton correlations, the relation being the analog of the AGK cancellation for the average number of soft interactions in high energy hadron–nucleus collisions. Finally, an infrared problem which finds a solution within the self-shadowing representation of the semihard cross section is discussed.

Study of fast target protons in high energy hadron-nucleus collisions

Intranuclear cascade model calculations are carried out on the recent measurements (WA80 Collaborations) for the multiplicity, energy and angular distributions of singly charged target fragments of energy in the range 30 <E < 400 MeV (the so-called grey particles) produced in proton-nucleus interactions at 200 GeV/c. It is shown that these distributions are reasonably well understood in terms of the intranuclear cascade model which considers that grey particles are only produced in the first two generations of the cascade. The obtained distributions, mean values and target mass dependence are more consistent with the experimental data than other models using Monte Carlo Simulations.

J/ psi suppression in hadron-nucleus collisions.

We examine the production of J/$\Psi$ mesons in high energy hadron-nucleus collisions using models that account for both the initial state modification of parton distributions in nuclei and the final state interaction of the produced $c\bar c$ pairs. We show that, at the energies of current fixed target experiments, J/$\Psi$ production through quark-antiquark annihilation gives the largest contribution at $x_F > 0.5$, while gluon-gluon fusion dominates the production at smaller $x_F$. The observed J/$\Psi$ suppression at large $x_F$ is directly connected to nuclear shadowing in deeply inelastic scattering. We find that a $6\sim 8$mb $c\bar c$-nucleon cross section is needed to explain the data on J/$\Psi$ suppression if a simple incoherent multiple scattering formalism is used for the final state interactions.

Erratum: Multiplicity distributions in high-energy hadron-nucleus collisions. I. Formalism

Erratum: Multiplicity distributions in high-energy hadron-nucleus collisions. I. Formalism

Inclusion of correlations in the empherical selection of intranuclear cascade nucleons from high energy hadron-nucleus collisions

The very high energy (5 GeV to 20 Tev) hadron-nucleus differential particle production model found in the Monte Carlo transport code FLUKA87 has been adapted for inclusion in the transport code HETC88. The empirical selection of intranuclear cascade nucleons has been modified to provide simple correlations with the randomly selected number of hadron-nucleon collisions. A standard method of calculating the extension energy of the compound nucleus preceding an added evaporation step by assuming the particles are produced in a one-dimensional nuclear well is applied. This method, coupled with the above correlations, lead to improved correlations of the excitation energy with the A and Z of the compound nucleus, and then to greatly improved distributions of the residual nuclei following evaporation. The frequency distribution of low enegy ( β < 0.7) charged particles show good agreement with experiment for 200 GeV protons incident on emulsions. Average multiplicities of showe and grey particles after evaporation for protons and pions incident on several elements are also compared with experiment.

Multiplicity distributions in high-energy hadron-nucleus collisions. II. Phenomenology.

Multiplicity distributions in high-energy hadron-nucleus collisions. II. Phenomenology.

Multiplicity distributions in high-energy hadron-nucleus collisions. I. Formalism.

The problem of multiparticle production in hadron-nucleus collisions is formulated in a way consistent with the Gribov-Glauber theory for inelastic cross section on the one hand, while being the generalization of a particle production model for pp collisions on the other hand. The latter is the geometrical branching model that satisfactorily describes geometrical scaling and Koba-Nielsen-Olesen scaling. The formalism allows the incident hadron to be broken by the first collision. Dependences on the impact parameter b and the multiplicity of gray particles ${N}_{g}$ are carefully taken into account. The average multiplicity as a function of the number of inelastic collisions, whether holding b,${N}_{g}$ fixed, or integrated, is derived, and is shown to agree with the data with a universal slope parameter \ensuremath{\beta}. General formulas for the multiplicity distributions are obtained for produced particles as well as for shower particles. A universal property of particle production in hN and hA collisions based on effective interactions among many partons is discussed. The geometrical branching model is then further developed to make possible the determination of \ensuremath{\beta} to be 0.5.

Monte Carlo event generator MCMHA for high energy hadron-nucleus collisions and intranuclear cascade interactions

The Monte Carlo event generator for high energy hadron-nucleus (h-A) collisions has been developed, which is based on the multi-chain model. The concept of formation zone and the cascade interactions of secondary particles are properly taken account into this Monte Carlo code. Comparing the results of this code with experimental data, the importance of intranuclear cascade interactions becomes very clear.

Optical model for medium and high energy hadron-nucleus collisions.

The optical phase shift function is calculated to fifth order in a model in which center of mass correlations in the nucleus are taken into account. Differential cross sections are calculated for elastic scattering of protons by $^{4}\mathrm{He}$, $^{16}\mathrm{O}$, $^{58}\mathrm{Ni}$, and $^{208}\mathrm{Pb}$. The results are compared with exact Glauber calculations and with a simple ${t}_{0}$\ensuremath{\rho}-type approximation. The significance of the higher-order corrections is assessed.

Target dependence of production cross sections in high energy hadron-nucleus collisions

We present a simple space-time picture for the production of high-mass hadronic resonances and dilepton pairs in energetic hadron-nucleus collisions. We demonstrate that the apparent coherence in the resonance production in such processes finds a natural explanation in our model.

Hadron-nucleus scattering as a function of nuclear size

High-energy hadron-nucleus collisions, when viewed in terms of nuclear size, exhibit a remarkable simplicity. The data suggest that nuclear matter is extremely opaque to hadrons, and that fast-forward hadrons ( x≳0.3) arise solely from peripheral collisions. This picture naturally explains why the production ratios of different hadron species are target independent at large x.

Multisource model for particle production in high-energy hadron-nucleus collisions.

A multisource model for particle-production processes in high-energy hadron-nucleus collisions is presented. The model is an extension of the statistical model proposed some time ago by the Berliner group to describe such processes in hadron-hadron collisions at comparable as well as at higher energies. The concept of the effective target turns out to be very useful for this generalization to nuclear targets. The result shows in particular that the observed characteristic properties of multiplicity distributions, rapidity distributions, and correlations can be understood in terms of a physical picture in which the dynamical details of hadronic interactions do not play a significant role.

Angular and energy distributions of grey particles in high-energy hadron-nucleus collisions

The angular and energy distributions of grey particles (mostly protons in the energy range 30–400 MeV) emitted in the interactions of high energy hadrons with nuclei are investigated here. Grey particles “g particles” are assumed to result from the intranuclear cascade initiated by the passage of the incident hadron through the target nucleus. Using the pretested hypothesis that these particles arise only from the first two generations of the cascade, we calculate their angular and energy distributions. Various experimental data are successfully described both in shape and absolute magnitude.

Secondary particle spectra in hadron-hadron and hadron-nucleus collisions in the framework of the additive quark model and quark statistics

Secondary meson and baryon inclusive spectra in high-energy hadron-nucleon and hadron-nucleus collisions are calculated. We suggest that the fragmentation hadrons are produced as a result of the spectator mechanism and that their distributions imitate those of the quark-spectator. Sea hadron distributions are supposed to be similar to that of the hadron ones ine+e− annihilation. Particle production ratios are borrowed from statistic rules. Comparison with the experiment manifests the success of the quasinuclear quark structure of hadrons.