On the spin-isospin response at intermediate energies

We have calculated the response function of infinite nuclear matter to a spin-isospin probe in the transverse and longitudinal channels. The two channels are distinguished by the meson exchanged (ρ or π, respectively) in the ph and Δh interactions, in addition to the effective g′ interaction. In the intermediate-energy region the response is particularly sensitive to the Δ-dynamics in the nuclear medium. We have applied the results of a previous calculation, which is based on a self-consistent treatment of π- and Δ-propagation in nuclear matter, to obtain Δ-self-energy corrections in the medium. Due to the opening of many-body decay channels, the self-consistent mechanism supplies a strong quenching and spreading effect on the Δ-peak in the transverse channel and we find a remarkable contribution to the response function in the energy region corresponding to the dip in inelastic electron scattering. A comparison with the experimental data for the ¹²C(e, e') cross section is given. In the longitudinal channel, on the other hand, the coherent propagation of the intermediate pion has the effect of splitting the Δ-peak into two parts, due to the vanishing of the polarization propagator at the energy corresponding to the on-mass-shell pion. The self-consistent calculation again yields a quenching effect on the response which is particularly strong on the lower peak and pushes up the other one to higher energies.     

On photonuclear reaction mechanisms at intermediate energies

The¹²C(γ,2N) reactions have been studied using tagged photons ofE _γ = 114–600 MeV at the Mainz microtron (MAMI). The cross sections of the¹²C(γ,pn) reaction and the shape of¹²C(γ,pp) spectra compare well to model predictions over a wide range of photon energies and missing energies, suggesting that the dominant mechanisms of photonuclear reactions are understood.     

On the projectile fragmentation in heavy-ion reactions at intermediate energies

The two-body fragmentation of the projectile in the target field is described within a three-body dynamic model. Four types of reaction emerge: fusion at low energies and low impact parameters b, elastic and inelastic reactions at high b and two types of fragmentation in peripheral collisions. For high b the two projectile parts are emitted while for low b one fragment fuses with the target and only the other one can be detected. In the first case the part which has grazed the target has been strongly slackened and has a velocity of 0.7 V beam for small emission angles to 0.5 V beam for large angles. It might be a contribution to the relaxed fragment events detected at intermediate angles. In agreement with experimental data, the b² window for this kind of fragmentation is very narrow for heavy quasi-projectiles and widens with decreasing masses. This model allows to reproduce semi-quantitatively the mass distribution of the quasi-projectiles, the position of the maximum in the one- and two-peak energy spectra and the relative importance of the two types of fragmentation.     

124Sn target residues in the interaction of heavy ions at intermediate energies

Cross sections, recoil energy distributions for residues produced by¹⁴N,²⁰Ne,⁴⁰Ar on¹²⁴Sn targets have been measured in the 10–70 MeV/u intermediate energy range. As the projectile energy increases, processes as complete fusion-evaporation, incomplete fusion-evaporation and intranuclear cascade-evaporation participate progressively in the nuclear collisions. Peculiar residues corresponding to a gain of 4, 5 or even 6 protons for the¹²⁴Sn target have been observed in the 30–50 MeV energy range.     

Transient phenomena at intermediate energies

Considering the experimental energy behaviours of elastic K⁺p, pp, πp, polarizations, we show that in helicity-flip amplitudes non-leading contributions, non-identifiable with absorptive corrections, Regge-Regge cuts or resonance tails, remain non-negligible up to ～ 10 GeV/c. The interpretation of such contributions appears uncertain.     

Microscopic approach to calculating cross sections and optical potentials for nucleus-nucleus interaction at intermediate energies

Nucleus-nucleus scattering is considered in the high-energy approximation and on the basis of Glauber-Sitenko microscopic theory in the optical limit. Analytic expressions for eikonal phase shifts are given for the case of Fermi-type realistic potentials and nuclear-density distributions. The effect of taking into account the distortions of the trajectories of the nuclei involved and the nuclear-density dependence of nucleon-nucleon forces on the total reactions cross sections is illustrated. The sensitivity of the reaction cross sections to the choice of model for the ⁶He projectile nucleus, which involves a neutron halo, is explored. Semimicroscopic optical potentials are introduced in order to describe differential cross sections for elastic scattering. The results of the present calculations are compared with available experimental data.     

On lepton pair production in proton-antiproton collisions at intermediate energies

The lepton pair production via the quark-antiquark annihilation subprocess in collisions of beam antiproton with the proton target at E _beam = 14 GeV is studied on the basis of the event sample simulated by PYTHIA6 generator. Different kinematical variables which may be useful for the design of the muon system and the electromagnetic calorimeter of the detector of PANDA experiment at FAIR, as well as for the study of proton structure functions in the available x-Q ² kinematical region, are considered. It is also argued that the measurement of the total transverse momentum of a lepton-antilepton system may provide important information about the intrinsic transverse momentum 〈k _T 〉 that appears due to the Fermi motion of quarks inside the nucleon. Another interesting possibility is the measurement of the production rate of two or three lepton pairs in one event that can give the information about the rate of multiple quarks interactions and the proton space structure. The problems due to the presence of fake leptons that appear from meson decays, as well as due to the contribution of background QCD processes and minimum bias events, are also discussed. The set of cuts which allows one to separate the events with the signal lepton pairs from different kind of background events is proposed. The article is published in the original.     

Alpha-nucleus elastic scattering at intermediate energies

Elastic scattering of 288,340,480 and 699 MeV Alpha-particles was measured on ²⁰⁸Pb, ¹¹⁶Sn and ⁵⁸Ni. The data were analysed in terms of a phenomenological optical model. The optical potentials obtained were found to vary consistently with the target nucleus and the incident energy. The radial zone where the potentials are well determined was studied in detail. The data for ²⁰⁸Pb were also analysed with a folding model. The energy dependence of the strong-absorption radius and of the reaction cross section shows that the nuclear surface becomes slightly transparent for incident energies above 150 MeV per nucleon.     

Deuteron-proton elastic scattering at intermediate energies

The deuteron-proton elastic scattering has been studied in the multiple-scattering expansion formalism. Primary attention has been given to such relativistic problems as a deuteron wave function in a moving frame and transformation of spin states due to Wigner rotation. Parametrization of the nucleon—nucleon t matrix has been used to take the off-energy-shell effects into account. The vector, A _y , and tensor, A _yy , analyzing powers of the deuteron have been calculated at two deuteron kinetic energies: 395 and 1200 MeV. The obtained results are compared with the experimental data. The text was submitted by the authors in English.     

Positron-helium elastic scattering at intermediate energies

Total cross sections for elastic positron-helium collisions have been computed and compared with other theoretical results. Integrated cross sections over small angular regions extending from zero angle, for which a set of experimental estimates is available, are also presented.     

A new contribution to deuteron screening at high energies

Effects arising from the structure of the Pomeron are shown to lead to a decrease in the apparent size of the Glauber screening correction to the π-d total cross section. This decrease is large enough to partially cancel effects arising from the usual inelastic intermediate state corrections to Glauber.     

On screening effects in pair production at intermediate and high energies

The effect of screening in atomic field pair production is calculated in Born approximation without approximation as to energy or angle and compared with the results of previous calculations based on the high energy approximation. The difference between the two calculations is comparable to the errors in recent experiments. The effect of nuclear excitation on the total pair production cross section is also investigated, but is found to be extremely small.     

On the contribution of stopping protons to the rise in the proton-proton inelastic cross-section at high energies

It is shown that existing production data on protons and antiprotons from proton-proton collisions allow for a substantial contribution to the rise in the pp inelastic cross-section from incoming protons which lose almost all their energy (stopping protons).     

Evolution of intranuclear collisions at intermediate energies

The experimental data on energy and multiplicity distributions of protons and momentum spectra of deuterons emitted in the reactions of pions and protons of energy ranging from 2.5 to 200 GeV with several nuclei are compared to the calculations based upon two different model approaches: DCM Monte Carlo [3] code and the tube-fireball (TF) model [4]. The results of this confrontation are discussed within the framework of the intranuclear interaction mechanism assumed. A detailed study of the intranuclear scenario presented by the DCM Monte Carlo program gives grounds to build simplified analytic models like the TF which may turn out to be very useful in many practical problems as being of a predictive nature. The text was submitted by the authors in English.     

Photospallation of51V at intermediate energies

The yields of⁵¹V(, xpyn) reactions have been measured at maximum bremsstrahlung energies from 75 to 800 MeV. Mean cross sections have been deduced, compared to Monte-Carlo calculations and analysed with a semiempirical Rudstam formula. Total isobaric mean cross sections and anN/Z dispersion curve in the mass regionA = 42–48 have been obtained. The results are in agreement with cascade-evaporation theory and with earlier data obtained with photons and protons.