Fast deuteron production in proton-nucleus interactions

Deuteron formation in proton-nucleus reactions due to the coalescence mechanism with final-state interaction between nucleons is discussed in order to establish the kinematical region of the validity of this approach. The experimental data on fast deuteron production in proton-nucleus collisions at bombarding energies above 3 GeV are analyzed. It is shown that most experimental results were obtained for deuteron momenta below the critical limit of the coalescence model. It is discussed to which extent further experimental studies could help to identify contributions from the coalescence mechanism and to get better understanding of the fast deuteron-production process.This article was processed by the author using the LATEX style filepljour2 from Springer-Verlag.     

Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions

It is well known that noncentral nuclear forces, such as the spin–orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known because only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may convey useful information about the in-medium properties of noncentral nuclear interactions, besides earlier studies using the time-dependent Hartree–Fock approach to understand the effects of spin–orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore the dynamical effects of noncentral nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focus of these studies has been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies but so far there are still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.     

Nuclear effects in multiparticle production in 800 GeV and 400 GeV proton-nucleus interactions

We study nuclear effects in multiparticle production in proton-emulsion nuclei interactions at 800 GeV and 400 GeV. The observed pseudorapidity distributions are compared with the predictions of a simple quark model. The predicted dependence of the ratio of the normalised multiplicity distribution of the produced shower particles in hadron-nucleus (hA) to hadron-hadron (hh) interactions on the mean number of inelastic collisions in the central region is in good agreement with the experimental data.     

Inclusive K+-meson production in proton-nucleus interactions

The production of K⁺-mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-Jülich for beam energies T_p = 1.0-2.3 GeV. Double differential inclusive pC cross-sections at forward angles _{K^+} < 12^° as well as the target mass dependence of the K⁺ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T_NN = 1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target mass dependence of the cross-sections at higher energies, the repulsive in-medium potential of the K⁺-mesons can be deduced. Using pN cross-section parameterisations from the literature and our measured pD data we derive a cross-section ratio (pnK⁺X)/(ppK⁺X) (3-4).     

Spin effects in inelastic proton-nucleus scattering

We include the spin-orbit force in the analysis of inelastic proton-nucleus scattering. In the limit of zero-range nuclear forces, very simple results are obtained. To lowest order in the elementary spin-orbit amplitude, the spin-dependent nuclear amplitudes are proportional to the momentum transfer times the spin-independent nuclear amplitudes. Consequently, in the spin-independent cross section the region of the diffractive minima is not significantly affected by the elementary spinorbit amplitudes, whereas the subsidiary maxima are somewhat enhanced.     

Multiplicity in proton-nucleus interactions in emulsion at 800 GeV

The experimental data on multiplicities of charged particles of different type produced in incoherent interactions of 800 GeV proton with emulsion nuclei are reported and discussed. The data are compared with the results of other experiments on protonnucleus collisions at lower energies. It is shown that the Lund model describes well the data on multiplicities of relativistic particles.     

Spin-rotation effects in elastic proton-nucleus scattering

We discuss a particular form of spin-rotation distribution in the context of proton-nuclear scattering and indicate its behaviour as a function of momentum transfer. We point out that besides effectively completing our knowledge of the nuclear scattering amplitudes the measurement of this function would furnish information both about the nuclear density distribution and about parts of the fundamental proton-nucleon spin-orbit scattering amplitudes. The latter are terms of the amplitudes which have been left undetermined by existing polarization data.     

Initial-state nuclear effects in proton-nucleus collisions

Two important initial-state nuclear effects in hadron-nucleus collisions are considered. The ratios of inclusive differential cross-sections for Drell-Yan dimuon production are calculated. The calculated results are compared to the E866 data. It is shown that the consideration of multiple soft rescatterings of incident quarks in nuclei and initial-state quark energy loss effects allow to get a good agreement between the calculated results and the experimental data.     

Negative binomial distributions and clan model in proton-nucleus interactions

Experimental results on multiplicity distributions in different pseudorapidity intervals of charged shower particles produced in proton-AgBr and proton-CNO collisions at 800 GeV are presented. The different distributions are described well by the negative binomial form. We successfully interpret our results in terms of the clan model. The values of the rapidity gap probability in terms of average number of clans in different pseudorapidity intervals are also determined.     

Two-particle rapidity correlations in proton-nucleus interactions at 300 GeV

The single- and two-particle inclusive rapidity distributions for proton-nucleus interactions at 300 GeV in nuclear emulsions are presented. The analysis of the data with the two-particle rapidity correlation function R(ν₁, ν₂) shows clear evidence of short range correlations. A remarkable asymmetry between projectile and target hemisphere is found.     

Angular distributions in proton-nucleus interactions in emulsion at 800 GeV

Data on angular distributions of heavily ionizing and shower particles in incoherent protonnucleus collisions in emulsion at 800 GeV are reported and discussed in details. Dependence of angular distributions on the mass number of a target nucleus and on the multiplicity of charged particles is investigated. The data presented are systematically compared with results of emulsion experiments at lower energies and with predictions of the Lund Monte Carlo model FRITIOF.     

Pionization effects in proton-nucleus total cross sections

A simple unitary model for meson production effects in proton-nucleus scattering was used earlier to estimate the pionization corrections to the proton-deuteron total cross section. This model is here used to study the corresponding effects in heavy nuclei using a generalization of the optical limit. An increase in the total cross sections at the upper limit of NAL energies of roughly 20% is found.     

Neutron experiments to search for new spin-dependent interactions

The consideration is presented of possible neutron experiments to search for new short-range spin-dependent forces. The spin-dependent nucleon-nucleon interaction between neutron and nuclei may cause different effects: phase shift of a neutron wave in neutron interferometers of different kind, in particular of the Lloyd mirror configuration, neutron spin rotation in the pseudo-magnetic field, and transverse deflection of polarized neutron beam by a slab of substance. Estimates of sensitivity of these experiments are performed.     

Observation of multiparton interactions in proton-nucleus collisions at 70 GeV

The production of noncoplanar hadron pairs in proton-nucleus interactions is studied experimentally for the case where the transverse momenta of product particles are in excess of 1 GeV/c. The values obtained for the exponent in the A dependence of the cross section for the production of noncoplanar hadron pairs are substantially greater than those for coplanar pairs. This nuclear-mass-number dependence for the production of hadron pairs can be explained by the contribution of multiparton interactions in proton-nucleus collisions.     

Clan structure and intermittency in proton-nucleus interactions at high energy

In this paper we examine the similarity between clan structure and self-similar cascading in high energy proton-nucleus interactions at 70 GeV/c in emulsion. The investigation shows that the negative bionomial fitting parameterk can be used for the evaluation of factorial moments in intermittency studies and that these exhibit similar behaviour with those derived from nonstatistical procedure. The results of our study signify compatibility between clan cascading and self-similar cascading in soft hadroization processes.     

Noncomplanarity effects in the one-dimensional spin-dependent scattering

The scattering of a spin-polarized quantum wave on a potential barrier is investigated. The vectors of spin-polarization of incident wave and the internal magnetic field (magnetization) of the barrier are not generally located in the same plane and they form a noncomplanar system. The dependences of the polarization vectors of waves scattered forward and backward on the degrees of freedom determining the orientation of the barrier magnetization are investigated.