Dilepton production in proton-nucleus and nucleus-nucleus collisions at SPS energies

Dilepton production in proton- and nucleus-induced reactions is studied in the relativistic transport model using initial conditions determined by the string dynamics from RQMD. It is found that both the CERES and HELIOS-3 data for dilepton spectra in proton-nucleus reactions can be well described by the ‘conventional’ mechanism of Dalitz decay and direct vector meson decay. However, to provide a quantitative explanation of the observed dilepton spectra in central S+Au and S+W collisions requires contributions other than these direct decays. Introducing a decrease of vector meson masses in hot and dense medium, we find that these heavy-ion data can also be satisfactorily explained. This agrees with our earlier conclusions based on a fire-cylinder model. We also give predictions for Pb+Au collisions at 160 GeV/nucleon using current CERES mass resolution and acceptance.     

Heavy fragments produced in proton-nucleus and nucleus-nucleus collisions at relativistic energies

Mesons, nucleons and light and heavy nuclei are observed as a result of a proton-nucleus or a nucleus-nucleus collision at relativistic energies (E_p≥0.5 GeV/u). This review concentrates on the properties of the heavy fragment nuclei (A ≥10. The experimental results for the distributions in mass, charge, angle and kinetic energy are presented. The data are discussed in the framework of models for spallation, fission and multifragmentation.     

Projectile fragmentation in hadron-nucleus collisions at high energies

Particle production in hadron-nucleus collisions at high energies is discussed in the projectile fragmentation region. The predictions of the constituent quark model are analyzed. The contribution of diffractive interactions is explicitly taken into account. Comparison with the recent Fermilab measurements shows good agreement with the quark model and strong effects of diffractive collisions in some of the analyzed reactions.     

Approximate description of multiple scattering in nucleus-nucleus collisions at high energies

A new expression for the nucleus-nucleus profile function, obtained by symmetrizing the rigid nucleus approximation, is presented. The equivalence of the “rigid target” and “swarm projectile” approximations is shown.     

Self-similarity of low-p T cumulative pion production in proton-nucleus collisions at high energies

The experimental data on inclusive spectra of the π⁺ mesons produced in p + A collisions at the incident proton momentum of 400 GeV/c obtained by G. Leksin group at FNAL are analyzed in the framework of z-scaling. Self-similarity of the hadron production in the low-p _T cumulative region is verified. Scaling function ψ(z) for the Li, Be, C, Al, Cu, Ta nuclei is constructed. It is expressed via the invariant cross section and average multiplicity density of charged particles. Results of the analysis of the low-p _T data are compared with the high-p _T data sets obtained by J. Cronin, R. Sulyaev and D. Jaffe groups. A microscopic scenario of p + A interactions in terms of momentum fractions x ₁, x ₂ is discussed. Indication on self-similarity of the cumulative pion production in p + A collisions over a wide kinematical range has been found. Based on the universality of the shape of the scaling function the inclusive cross sections of the π⁺ mesons produced in p + A collisions on the Li, Be, C, Al, Cu, Ta targets in deep-cumulative region (x ₂ ? 1/A) are predicted.     

Limiting fragmentation in hadron–hadron collisions at high energies

Limiting fragmentation in proton–proton, deuteron–nucleus and nucleus–nucleus collisions is analyzed in the framework of the Balitsky–Kovchegov equation in high energy QCD. Good agreement with experimental data is obtained for a wide range of energies. Further detailed tests of limiting fragmentation at RHIC and the LHC will provide insight into the evolution equations for high energy QCD.     

Proton and triton momentum distributions from4He fragmentation at relativistic energies

The 0° differential cross sections of the¹²C(⁴He,p) and¹²C(⁴He,t) reactions have been measured at beam momenta of 4.52 and 2.69 GeV/c/nucleon, respectively. The proton and triton momentum distributions in⁴He are extracted from the cross sections using a relativistic impulse approximation. Some theoretical models based on realisticN-N potentials are examined for our data.     

Transverse mass distributions in central heavy-ion collisions at high energies

The transverse mass spectra of protons, pions, kaons, Lambda and Antilambda produced in cen- tral nucleus-nucleus collisions at high energies are described by using one-temperature and two-temperature emission pictures. The calculated results are compared and found to be in good agreement with the experimen- tal data of the E895, E866 and E917 Collaborations measured in central Au-Au collisions at the Alternating Gradient Synchrotron (AGS) energies and the NA49 Collaboration measured in central Pb-Pb collisions at the Super Proton Synchrotron (SPS) energies. It is demonstrated that the transverse mass distributions of protons, kaons, Lambda and Antilambda, except for Lambda hyperons produced in central Pb-Pb collisions at 158 A GeV, can be described by using the one-temperature emission picture, and for pions, we need to use the two-temperature emission picture.     

Transverse mass distributions in central heavy-ion collisions at high energies

The transverse mass spectra of protons, pions, kaons, Lambda and Antilambda produced in central nucleus-nucleus collisions at high energies are described by using one-temperature and two-temperature emission pictures. The calculated results are compared and found to be in good agreement with the experimental data of the E895, E866 and E917 Collaborations measured in central Au-Au collisions at the Alternating Gradient Synchrotron (AGS) energies and the NA49 Collaboration measured in central Pb-Pb collisions at the Super Proton Synchrotron (SPS) energies. It is demonstrated that the transverse mass distributions of protons, kaons, Lambda and Antilambda, except for Lambda hyperons produced in central Pb-Pb collisions at 158 A GeV, can be described by using the one-temperature emission picture, and for pions, we need to use the two-temperature emission picture.     

Microscopic theory of photon production in proton-nucleus and nucleus-nucleus collisions

The production of energetic photons in medium-energy proton and heavy-ion induced reactions is studied on the basis of incoherent nucleon-nucleon collisions. For this purpose we first evaluate covariantly the photon production from proton-neutron collisions in a vector (ω) and scalar meson (σ) exchange model with coupling constants given by the M2Y G-matrix in the nonrelativistic limit. We furthermore follow the proton-neutron collisional history by means of a phase-space simulation based on the Boltzmann-Uehling-Uhlenbeck approach for proton-nucleus and nucleus-nucleus collisions adding up incoherently the yields from each individual collision. The satisfactory agreement we obtain in comparison with experimental data allows to conclude that energetic photons predominantly arise from proton-neutron bremsstrahlung during the early stage of the collision.     

Multiplicity distributions in proton-nucleus collisions at 67 and 200 GeV

New data, concerning multiplicities in collisions of 67 and 200 GeV protons in emulsions are presented. Various parameters of multiplicity distributions in collisions of protons with nuclei of photographic emulsion at primary energies between a few and about 1000 GeV are compared with p-p collisions.     

Production of charged kaons in proton-nucleus and nucleus-nucleus collisions at 200 GeV/nucleon

Production of charged kaons in proton-sulphur, proton-gold, sulphur-sulphur and oxygen-gold collisions at 200 GeV/nucleon has been studied in the NA35 Streamer Chamber experiment. Rapidity and transverse mass distributions as well as mean multiplicities were obtained. The results are compared with nucleon-nucleon data and with model predictions.Deceased     

Baryon distributions in ultrarelativistic nucleus-nucleus collisions

We have measured distributions in transverse momentum and rapidity of protons from interactions of 14.6 GeV/nucleon²⁸Si projectiles with targets of Al and Pb. The transverse momentum spectra exhibit a thermal shape with a rapidity dependent temperature parameter. For very central or violent collisions the proton rapidity distributions exhibit the large rapidity shifts and (for Si+Al) a peak at midrapidity as required for full stopping.     

Theory of fragmentation dynamics in nucleus-nucleus collisions

The fragmentation of a nuclear system is described by a dynamical coordinate, the fragmentation coordinate η=A₁?A₂/A₁+A₂ The total Hamiltonian describing a binary heavy ion encounter includes a part H(R, α,η) which describes the fragmentation and its coupling to other degrees of freedom. It is a collective Hamiltonian which is calculated from the microscopic Asymmetric Two-Center Shell Model (ATCSM). The properties of this Hamiltonian are extensively discussed and methods for its solution are described. Formulae for cross sections of specific nuclear fragmentations including fusion are derived.     

Transverse momentum spectra in high-energy nucleus-nucleus, proton-nucleus and proton-proton collisions

The transverse momentum distributions of final-state particles produced in nucleus-nucleus (AA), proton-nucleus (pA), and proton-proton (pp) collisions at high energies are investigated using a multisource ideal gas model. Our calculated results show that the contribution of hard emission can be neglected in the study of transverse momentum spectra of charged pions and kaons produced in Cu-Cu collisions at √s_NN=22.5 GeV. And if we consider the contribution of hard emission, the transverse momentum spectra of p and p produced in Cu-Cu collisions at √s_NN=22.5 GeV, K_s⁰ produced in Pb-Pb collisions at 158 A GeV, J/ψ particles produced in p-Pb collisions at 400 GeV and π⁺ , K⁺, p produced in proton-proton collisions at √s=200 GeV, can be described by the model, especially in the tail part of spectra.