Production In Nuclear Collisions Research Articles

Strange particle production in nuclear collisions at 200 GeV per nucleon

Multiplicities and spectra of strange particles (\(\Lambda ,\bar \Lambda ,K_S^0 ,K^ +\) andK− produced in central32S+S,32S+Ag and32S+Au collisions at 200 GeV per nucleon are presented and compared with data on strange particle production in protonnucleus and nucleon-nucleon interactions. It is shown that strangeness production in32S+Ag collisions is enhanced by a factor of two, similar to that found previously in central32S+S collisions.

Meson production in nuclear collisions and the equation of state of hadronic matter

Meson production in nuclear collisions and the equation of state of hadronic matter

SCALING PATTERN FOR PARTICLE PRODUCTION IN HEAVY-ION COLLISIONS AT SUB-THRESHOLD BEAM ENERGY

We examine the experimentally observed scaling patterns for particle production in nuclear collisions at sub-threshold energy regime in the framework of a cooperative model. Besides π+, K+, K− and [Formula: see text] we also include protons emitted at extreme kinematical region. We show that the proton spectra also has the same universal scaling behavior as that of pions, kaons and antiprotons. This supports our earlier proposition that the reaction mechanism leading to the emission of proton in extreme kinematical region is similar to the ones which cause sub-threshold particle productions.

Particle production in nuclear collisions and string interactions

It is shown that if strings fuse as they overlap in the interaction transverse are available, this will produce a peculiar behaviour with the energy of the single and double inclusive cross-sections in h A and AB collisions, which can be detected experimentally.

High P t strangeness enhancement

Enhanced strangeness production in nuclear collisions has been proposed as a possible signature of quark-gluon plasma formation: in particular, the φ production might increase. We find, however, that the enhancement of the φ/( ϱ 0+ ω) ratio by a factor of ca. 3 observed by NA38 (for p ⊥≥ 1.1 GeV) can be explained by the smaller size of the φ absorption cross section and that the enhancement of the φ to cortinuum ratio could be an artifact of the p t cutoff applied to the data.

Soft-pion emission in high-energy heavy-ion collisions.

We revive Heisenberg's approach to multiparticle production in the context of soft-pion emission in heavy-ion collisions. Adopting appropriate boundary conditions, we find a general analytic solution of the classical equations of motion for the nonlinear $\ensuremath{\sigma}$ model (for soft pions this model is an approximation to QCD). The solution is used to discuss various features of soft pion production in nuclear collisions.

The pT-dependence of [formula omitted] production in nuclear collisions as a result of quantum dissolution combined with initial state interactions

It has been argued that the more realistic, quantum treatment of the problem of J ψ dissolution in a quark-gluon plasma leads to a suppression pattern which is too weakly p T-dependent. We show, however, that when combined with initial state interactions, the quantum description accounts for the p T distribution of J ψ 's observed in nucleus-nucleus collisions.

Pion production in nuclear collisions

The production of pions in nuclear collisions is analyzed in terms of a microscopic reaction model, where the free energy of the entrance channel is transferred to the final channel through the coupling of the relative motion to the internal excitation of N*-resonances. Such a model allows quite naturally for a consistent analysis of the exclusive and the inclusive production of pions. It turns out that the pionic fusion cross section is determined predominantly by the spectroscopic parentage between the initial target projectile combination and the final nucleus, whereas the inclusive part is dominated by the energy dependence of the phase space factor, i.e. by the number of the degrees of freedom which are relevant in a given kinematical situation. This model is applied to the analysis of available experimental data from threshold to the Δ(1232)-region. A consistent analysis of both the inclusive and the exclusive part of the pion spectrum is presented.

ø enhancement in nuclear collisions

Enhanced strangeness production in nuclear collisions has been proposed as a possible signature of quark-gluon plasma formation: in particular, the ø production might increase. We find however that the observed enhancement of the ø/(ϱ 0 + ω) ratio observed in relativistic heavy ion collisions at CERN, might be due to the smaller size of the ø absorption cross section and that the enhancement of the ø to continuum ratio could be an artifact of the p t cutoff applied to the data. We suggest that high p t vector mesons at midrapidity, once created in primary collisions, can only be depleted by absorption in secondary collisions and not recreated: no real enhancement of ø production would be expected and in fact none may be needed to explain the data.

Systematics of J/ψ production in nuclear collisions

We present a comprehensive QCD-based model for the x f and nuclear dependences of heavy quarkonium production in photon-, hadron-, and nuclear-induced collisions. The calculated x f dependence reflects both leading-twist QCD fusion subprocesses and higher-twist intrinsic heavy-quark components of the hadron wavefunction. A-dependent effects due to final-state absorption, interactions with comovers, shadowing of parton distributions, and intrinsic heavy-quark components are identified. The model is compared with data for J/ ψ, ψ 1 and ϒ production in pion,proton, and nucleus-nucleus collisions.

Initial state effects on dilepton production in nuclear collisions

For hadron-nucleus collisions, multiple elastic scattering of the incident parton inside the nucleus leads to a broadening of the PT distribution for high mass dilepton production. Such a broadening has been used to explain the PT-dependence of the J/ψ suppression observed in high energy O — U and S — U collisions. Precision measurements of the A-dependence of dilepton distributions from h — A collisions can provide a test of this explanation. Furthermore, a comparison of the PT-dependence of J/ψ and Drell-Yan production in nucleus-nucleus collisions, as a function of ET, can be used to distinguish between quark deconfinement and hadronic absorption as the origin of the observed J/ψ suppression.

Initial state effects on dilepton production in nuclear collisions

For hadron-nucleus collisions, multiple elastic scattering of the incident parton inside the nucleus leads to a broadening of the p t distribution of high mass dilepton production. Such a broadening has been used to explain the p t dependence of the J/ ψ suppression observed in high energy O - U and S - U collisions. Precision measurements of the A-dependence of dilepton distributions from h - A collisions can provide a test of this explanation. Furthermore, a comparison of the P T -dependence of J/ ψ and Drell-Yan production in nucleus-nucleus collisions, as function of E T -can be used to distinguish between quark deconfinement and hadronic absorption as origin of the observed J/ ψ suppression.

Transverse energy dependence of dilepton production in nuclear collisions as a signature of quark-gluon plasma formation

The dependence of dilepton production on total transverse energy in nuclear collisions is proposed as a signature of quark- gluon plasma formation. In particular the ratio of dilepton production in central (large transverse energy) to that in peripheral (low transverse energy) gives information about the presence of hydrodynamical space-time evolution of the quark-gluon plasma or of a mixed phase.

The PT dependence of dilepton production in nuclear collisions

The P T distribution of massive lepton pairs produced in hadron-nucleus (h− A) collisions becomes broader with increasing A. In a framework based on perturbative QCD, this effect can be interpreted as elastic initial-state parton scattering, and it is predicted to saturate for large A. We show that an extrapolation of this behaviour to nucleus-nucleus collisions is in accord with measured continuum (Drell-Yan) dilepton behaviour, but that it cannot account for the P T dependence of J/Ψ suppression. Consequently, the behaviour of 〈 P T 2〉 J/ Ψ / 〈 P T 2〉 D−Y in the large- E T region nuclear collisions provides a crucial test for the production of a quark-gluon plasma.

Multifragmentation versus sequential fission: Observable differences?

To elucidate the observable distinctions between different reaction mechanisms for multifragment production in nuclear collisions at intermediate energies, we contrast two opposite extremes: sequential binary fission and simultaneous multifragment breakup ( true multifragmentation). For identical multifragment channels produced by these two idealized mechanisms, we examine the kinetic-energy spectra and the correlated velocity distributions of the fragments and discuss the possibility of identifying informative multifragment observables.

Negative particle production in nuclear collisions at 60 and 200 GeV/nucleon

The results on spectra of negative particles produced in16O+Au andp-Au collisions at 200 GeV/nucleon and16O+Au at 60 GeV/nucleon are presented. The correlations of average rapidity and average transverse momentum with event multiplicity are studied. Spectral shapes are similar for central16O+Au andp-Au collisions. The transverse momentum and rapidity distributions for central16O+Au andp-Au collisions differ strongly from corresponding distributions forp+p interactions. The FRITIOF model fails to describe the shapes of the transverse momentum distributions. The simple thermodynamical model of a single fireball does not fit the midrapidity transverse momentum distributions, and the rapidity distributions.

High energy photon production in nuclear collisions.

High energy photons may be produced in nuclear reactions by several mechanisms, including bremsstrahlung from the potential field or from nucleon-nucleon collisions. Using infinite and semi-infinite nuclear matter approximations, we obtain simple expressions for the rates. Nucleon-nucleon collisions provide the more important mechanism for both proton-induced and heavy-ion induced reactions, except for the highest energy photons. The photon cross section calculated with a zero range np interaction agrees well with measurements on proton-induced reactions. For heavy-ion reactions, the initial np collisions only account for a third of the measured cross section. The disagreement may be due to an inadequacy of the infinite matter or the zero range approximations, or it may be that multiple collisions are important.

Models for new particle production in nuclear collisions

Following up our earlier work and also stimulated by recent experimental results on positron production in heavy ion collisions we investigate various mechanisms for the production of a light, previously unknown particle in such collisions. As more conventional mechanisms seem to be inadequate we concentrate on processes directly or indirectly connected with the strong electric or magnetic fields and quark degrees of freedom in nuclei. We also consider modifications of the color confinement scheme. Our analysis is confined to schemes staying within the framework of the standardSU(3)c ×SU(2)×U(1) model. Since most of the possibilities discussed can be rejected, severe modifications of basic concepts of particle physics seem to be required if the production of a new particle is confirmed.

Pion production in inelastic and central nuclear collisions at high energy.

A detailed study of pion production in inelastic and central nucleus-nucleus collisions was carried out using a 2 m streamer spectrometer. Nuclear targets mounted inside the streamer chamber were exposed to nuclear beams of 4.5 GeV/c/nucleon momentum. A systematic study of the influence of the central trigger on observed data is performed. The data on multiplicities, rapidities, transverse momenta, and emission angles of negative pions are presented for various pairs of colliding nuclei. Intercorrelations between various characteristics are studied and discussed. The results are compared with predictions of some theoretical models. It is shown that the main features of the pion production in nuclear collisions can be satisfactorily described by a model assuming independent nucleon-nucleon collisions with subsequent cascading process. However, the observed correlation between \ensuremath{\Lambda} and pion characteristics seems to be unexplained by this picture.

Hard photons from co-operative effects in intermediate energy heavy-ion collisions

The co-operative model developed earlier to study the pion production in nuclear collisions at intermediate beam energies has been extended to describe the spectra of hard photons measured in similar experiments. In this model the co-operative action of several of the target and projectile nucleons in the particle production is considered. It is found that the model provides a reasonable description of the experimental data. The results could imply that the mechanisms of the production of pions and hard photons are relatively similar. A proper account of the Bose-Einstein statistics for photons affects only the low energy parts of the photon spectra.