Production In Nucleus-nucleus Collisions Research Articles

Gluon multiple scattering and the transverse momentum dependence of J/ψ production in nucleus-nucleus collisions

A J/ψ meson is mainly formed by gluon fusion for 200 GeV pp collisions. In reactions with nuclei the gluons (g) scatter off other nucleons (N) before fusing to a J/ψ, which thenshows additional transverse momentum p T. Fitting the value of the parameter σ gN〈 p 2 T〉 gN to describe the gluon multiple scattering effect in proton-nucleus data, we can reproduce the p T distribution of J/ψ production in 200 GeV/ A nucleus-nucleus collisions. The origin of the p T distribution is traced to soft gluon radiation via the Sudakov form factor.

Strange particle production in nucleus-nucleus collisions at 4–5 GeV/c momentum per nucleon

The experimental data on Λ and K s 0 productions at 4.2 AGeV/c and 4.5 AGeV/c for various nucleus-nucleus collisions are presented. A special attention is paid to these effects which could not be explained on the basis of free nucleon-nucleon interactions.

Transverse energy distributions in nucleus-nucleus collisions in the dual Monte Carlo multi-chain fragmentation model

Particle production in nucleus-nucleus collisions is calculated in a Monte Carlo version of the dual multi-chain fragmentation model. The model uses an efficient method to sample the numbers of interactions in nucleus-nucleus collisions. We calculate distributions in the transverse energy and multiplicity and compare with data obtained at the CERN SPS in OPb collisions with 200 GeV per nucleon.

Peculiarities of ? hyperon and ??-meson production in nucleus-nucleus collisions at high energy

The analysis of the data on the production of Λ hyperons and π- in4He−Li,12C−C,12C−Ne and16O−Ne at 4.5 A GeV/c and12C−C collisions at 4.2 A GeV/c are presented. Kinematical features of Λ's are shown to depend on the collision centrality in contrast to the stable behaviour of the pion characteristics. The correlation between the characteristics of Λ's and accompanying pions is observed. The effects seem to be incompatible with the intranuclear cascade approach. The data suggest the formation of a fully stopped and thermalized hot source in central nucleus-nucleus collisions, in which Λ hyperons are produced.

Subthreshold pion production in nucleus-nucleus collisions

The production of neutral pions in nucleus-nucleus collisions has been observed at projectile energies down to 20 MeV/u; at such low energies the production of a pion requires a cooperative action of manu nucleons. Apparently the necessary conversion of energy out of the relative motion takes place in the early stage of the collision before thermalization. This fast process results in bremsstrahlung-like pion spectra and angular distributions. A non-equilibrium emission is suggested as well by the excitation function as by the dependence on target and projectile mass; the latter also indicates non-isotropic reabsorption of the emitted pions. The systematic data available presently form a rather complete basis for a consistent description of the pion production from nuclear reactions.

Lambda production in nucleus-nucleus collisions

Lambda production in nucleus-nucleus collisions

Pions and hard photons as probes for nucleus-nucleus collisions

Pion production in nucleus-nucleus collisions at energies from 20 MeV/u up to 84 MeV/u can be shown to be a largely cooperative effect. The spectra of neutral pions and high energy photons can be understood within the framework of a bremsstrahlung process in contrast to a statistical emission picture, which e.g. underpredicts the pion yield at V20 MeV/u as we have found in a recent experiment.

Comments on multiparticle production in nucleus-nucleus collisions

We discuss the following aspects of the field: similarities and differences of models, definitions of central collisions and correlations between the ratio n/D and the rise of the average transverse momentum with increasing multiplicity.

Subthreshold pion production in nucleus-nucleus collisions — A cooperative process!

We examine various reaction mechanisms to explain the pion production at “subthreshold” energies. They range from the single collision mechanism to a cooperative multi-nucleon process. With a shell-model prescription for the initial state energies the single collision picture cannot explain the data. Rather, the cooperative action of many nucleons and also the freezing of degrees of freedom in the final channel (formation of composite nuclei) are seen vital to understand the observed cross sections.

Proton production in nucleus-nucleus collisions at 400 MeV/nucleon: A possible explanation for the anisotropy in the inclusive spectra

We investigate proton inclusive production in nucleus-nucleus collisions at 400 MeV/ nucleon within the framework of a multiple collision approach based on sequences of independent baryon-baryon collisions. We take explicitly into account the beam energy dependence of the inverse slope of the elementary NN differential scattering cross section which turns out to be essential for a reasonable agreement with the data concerning the 30 to 90 degree ratio of the c.m. spectrum.

Entropy and composite particle production

The application of entropy to composite particle production in nucleus-nucleus collisions is reviewed. More entropy is generated in high energy nuclear collisions than is predicted from bulk dynamics, due to the surfaces which are effectively quite thick. The measured production of deuteronlike clusters agrees with theory based on independent nucleon dynamics. The entropy concept may also be useful at low energies to help characterize the breakup of nuclei. We find the region of instability of nuclear matter as a function of energy and density. We suggest that the unstable region is reached in nuclear reactions by an isentropic expansion of overstressed nuclear matter.

Largep T hadron production in nucleus-nucleus collisions

The previously presented relations between inclusive cross sections for nucleus-nucleus, nucleon-nucleus and nucleon-nucleon scatterings with largepT production were generalized to include effects of large momentum tail of nucleons inside the nucleus. Simple numerical estimations show that these effects are likely to dominate the inclusive cross section for nucleus-nucleus collisions at very largepT.

The importance of the reaction volume in hadronic collisions

The pair production in the thermodynamic model is shown to depend sensitively on the (hadronic) reaction volume. Strangeness production in nucleus-nucleus collisions is treated as an example.

Meson production in nucleus-nucleus collisions

Nucleus-nucleus collisions at cosmic ray energies are described in terms of nucleon-nucleon collisions. The average multiplicity for different types of reactions is predicted and compared with experimental observation.