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Two-proton correlation functions at small relative momentum have been systematically studied with the large solid angle detector DIOGENE at Saturne for interactions induced by Ne and Ar beams on various targets, and incident energies per nucleon ranging from 200 to 1000 MeV. From these distributions, informations on the space-time structure of the source have been derived as a function of the centrality of the collision, the target-projectile combinations and the incident energy, using the model of Koonin. Special attention has been devoted to take into account all experimental biases in order to get the distorted theoretical correlation curves before comparison to the experimental data. Other interesting conclusions have been obtained when comparing the extracted source radii to the dimensions of the overlapping volume of target by projectile in a pure geometrical model of the collision (clean cut geometry). Some results concerning fragment-fragment small angle correlations are also presented.

Recent results from the large solid angle detector “DIOGENE” at Saturne (Saclay), for Ne + A and Ar + A reactions at 400, 600 and 800 MeV per nucleon are presented. Several points are selected: 1) The particles azimuthal emission pattern (with respect to the reaction plane) exhibiting preferential out-of-plane emission at c.m. rapidities, 2) The presence of an appreciable amount of collective flow for asymmetric systems and even for (rather) small projectile masses, 3) The first measurements of “flow” and multiplicities for both positive and negative pions, 4) The first measurement of deltas in central relativistic heavy ion collisions.

Triple-differential cross sections of proton-like particles were obtained for Ne+NaF, Ne+Nb and Ne+Pb reactions at 800 MeV per nucleon from quasi-exclusive measurements. Their dependence upon the azimuthal angle with respect to the reaction plane is analyzed. In addition to the usual flow pattern, another component of the azimuthal dependence is observed. It can be parametrized using the second order parameters in Fourier series expansion. The dependence of this component upon transverse momentum, rapidity and impact parameter (multiplicity) is investigated.

Emission of light fragments at small angles is studied in relativistic heavy ion collisions using the Diogene plastic wall for both symmetrical and non-symmetrical target-projectile systems with 400 MeV per nucleon and 800 MeV per nucleon incident neon nuclei. Efficiency of multiplicity measurements in the small angle range for the selection of central or peripheral collisions is confirmed for asymmetric systems. Differential production cross sections of Z = 1 fragments show evidence for the existence of two emitting sources. The apparent temperature of each source is obtained from comparison with a thermodynamical model.

International audience; The reaction pp→pp$\pi$$^0$ has been investigated at the Satume accelerator using a transversely polarized beam of 800 MeV incident kinetic energy and the DIOGENE detector. We have measured the total cross section, the differential cross section as a function of the pion energy and the anisotropy parameter b. We find a strongly dominant contribution, greater than 90%, of the Delta resonance to this process. We have determined the analyzing power A$_y$ of the reaction and get negative values.

The results of intranuclear cascade calculations (ideal gas with two-body collisions and no mean field), complemented by a simple percolation procedure, are compared with experimental data on protons and light nuclear fragments ([ital d], [ital t], [sup 3]He, and [sup 4]He) measured in 400 and 800 MeV/nucleon Ne+Nb collisions using a large solid angle detector. The model reproduces quite well global experimental observables like nuclear fragment multiplicity distributions or production cross sections, and nuclear fragment to proton ratios. For rapidity distributions the best agreement occurs for peripheral reactions. Transverse momentum analysis confirms once again that the cascade, although being a microscopic approach, gives too small a collective flow, the best agreement being reached for [ital Z]=2 nuclear fragments. Nevertheless these comparisons are encouraging for further improvements of the model. Moreover, such an approach is easy to extend to any other models that could calculate the nucleon phase space distribution after the compression stage of the reaction, when light nuclear fragments emitted at large angles are constructed from percolation.

The momentum distributions with respect to the reaction plane for charged pions emitted in Ne-nucleus and Ar-nucleus collisions have been measured with the 4 π detector Diogene at the Saturn synchrotron. The reaction plane is estimated from the baryon momenta, using a standard technique for flow analysis. The pions exhibit a non-zero flow. For asymmetric systems, there is a preferential emission in the direction of the lighter (projectile) nucleus. Such a behaviour contradicts the predictions of INC calculations and is underestimated by QMD calculations which include mean field effects. It can be interpreted with a simple geometrical model in terms of absorption by the spectator nuclear matter.

Deuteron spectra at laboratory angles from 30\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{} were measured in \ensuremath{\alpha}+(Pb, Cu, and C) collisions at 800, 600, and 200 MeV/nucleon, and \ensuremath{\alpha}+(Pb and C) collisions at 400 MeV/nucleon. The coalescence relation between protons and deuterons was examined for the inclusive part of the spectra. The size of the interacting region was evaluated from the observed coalescence coefficients. The rms radius is typically 4--5 fm, depending of the target mass. The proton and deuteron energy spectra corresponding to central collisions were fitted assuming emission from a single source moving with a velocity intermediate between that of the projectile and the target. The extracted ``temperatures'' are independent of the nature of the emitted particle, indicating that the fragments have a common source. The best fits were achieved for 200- and 400-MeV/nucleon reactions. Spectra of deuteron-like pairs, including real deuterons and neutron-proton pairs that may be contained in a larger nuclear cluster, are compared to the prediction of an intranuclear cascade model incorporating a clustering algorithm based on a classical coalescence prescription. Best agreements between experimental and predicted deuteron-like spectra occur for 800- and 600-MeV/nucleon collisions.

Emission of light fragments at small angles is studied in relativistic heavy ion collisions using the Diogene plastic wall for both symmetrical and non-symmetrical target-projectile systems with 400 MeV per nucleon and 800 MeV per nucleon incident neon nuclei. Efficiency of multiplicity measurements in the small angle range for the selection of central or peripheral collisions is confirmed for asymmetric systems. Differential production cross sections of Z = 1 fragments show evidence for the existence of two emitting sources. The apparent temperature of each source is obtained from comparison with a thermodynamical model.

In order to study the nuclear collective flow, the triple differential momentum distributions of charged baryons are fitted to a simple anisotropic gaussian distribution, within an acceptance which removes most of the spectator contribution. The adjusted flow angle and aspect ratios are corrected for systematic errors in the determination of the reaction plane. This method has been tested with Monte Carlo simulations and applied to experimental results and intranuclear cascade simulations of argon-nucleus collisions at 400 MeV per nucleon.

A classical many-body model for heavy-ion collisions at high energy has been proposed earlier, and numerical calculations have been reported. An extension to include elementary inelastic pion processes is investigated here. Nucleons are treated as relativistic Dirac particles coupled to the isovector pion field through pseudoscalar γ 5 coupling. Following a Foldy-Wouthuysen transformation, the Heisenberg equations of motion are derived for the expectation values of the relevant operators. The expectation values are taken with respect to a factorized wave function. The factorization ansatz plus the narrow wave packet assumption leads to classical-like equations of motion for the nucleons and the meson field amplitudes. The Δ(3, 3) resonance is qualitatively reproduced. Parameters of the model include the momentum cut-off (i.e. form factor) and the coupling constant. These are adjusted to reproduce isospin-averaged π-nucleon cross sections.

Diogene, an electronic 4 pi detector, has been built and installed at the Saturne synchrotron in Saclay. The forward angular range (0 degree-6 degrees) is covered by 48 time-of-flight scintillator telescopes that provide charge identification. The trajectories of fragments emitted at larger angles are recorded in a cylindrical 0.4-m3 Pictorial Drift Chamber (PDC) surrounding the target. The PDC is inside a 1-T magnetic field; the axis of the PDC cylinder and the magnetic field are parallel to the beam. Good identification has been obtained for both positive and negative pi mesons and for hydrogen and helium isotopes. Multiplicities in relativistic nucleus-nucleus reactions up to 40 have been detected, limited mainly by the present electronics.

Cette serie d'exposes sur les collisions entre ions lourds dans la gamme du GeV/u a ete divisee en trois parties. La premiere est consacree aux donnees de type inclusif. A l'occasion d'une revue sommaire des resultats experimentaux acquis depuis une dizaine d'annees, on a tente d'en degager quelques caracteristiques essentielles qui sont discutees dans le cadre de modeles phenomenologiques simples. Evoluant vers des experiences plus complexes, on abordera alors les mesures de correlation a deux particules qui constituent notre deuxieme sujet. On a distingue les correlations a grand angle qui renseignent sur l'importance du mecanisme de diffusion simple nucleon-nucleon dans les collisions d'ions lourds et les correlations a faibles impulsions relatives, du type interferometrie nucleaire, susceptibles d'etre reliees a la dimension et au temps de vie de la source emissive. Le cas des mesons π et celui des protons sont traites separement. Quelques resultats concernant la production de noyaux instables, qui releve aussi de ce type de mesure, sont aussi presentees. La derniere partie de ce cours est centree sur la nouvelle generation d'experiences avec des detecteurs 4π. Les techniques d'analyse en variables globales et leurs applications a la mesure d'un ecoulement collectif dans les collisions d'ions lourds, un des aspects originaux de ces mesures exclusives, sont discutees en detail. Finalement, nous conclurons cette revue avec quelques indications concernant une nouvelle methode d'analyse en impulsions transverses dont on peut esperer qu'elle permettra une determination des sections efficaces differentielles triples non moyennees sur l'azimut du plan de reaction.

The fragments emitted in the reaction 107,109Ag+20Ne at 175 and 252 MeV bombarding energy have been identified in charge up to Z = 32. Kinetic energy distributions, cross sections and angular distributions have been measured for each Z. The kinetic energy spectra show the two usual components: the quasielastic component and the relaxed component. The Z-distribution of the latter is fairly flat, slowly decreasing up to Z ≈ 15 and then rising again up to Z = 30. The variations in the Z-distribution are more pronounced at the lower bombarding energy. The angular distributions associated with the relaxed component are forward peaked for Z-values close to that of the projectile and behave like 1sinθ for larger Z-values. The forward peaking is very substantial for Z 10 the forward peaking in excess of 1sinθ disappears around Z = 15. These features are interpreted in terms of a diffusion process along the asymmetry coordinate of a short-lived intermediate complex.

The particles emitted in the reaction induced by 40 Ar on natural Ag at 288 and 340 MeV bombarding energy have been studied. The fragments have been identified in atomic number, their kinetic energy distribution and their angular distributions have been measured. The kinetic energy spectra show two components: a high-energy component related to the beam energy, or “quasi-elastic” component, and a low kinetic energy component, close to the Coulomb energy called “relaxed” component. The relaxed component is present at all angles and for all particles. The quasi-elastic component is present close to the grazing angle for atomic numbers close to that of the projectile. The relaxed cross section increases with atomic number for Z > 9. The increase in cross section is sharper for the lower bombarding energy. The angular distributions are forward peaked, in excess of 1 sin θ for all the measured atomic numbers. The forward peaking is larger for particles close in Z to the projectile. The results are interpreted in terms of characteristic times associated with a short-lived intermediate complex. The cross sections and angular distributions are satisfactorily reproduced on the basis of a model accounting for a diffusion process occuring along the mass asymmetry coordinate of the intermediate complex.

Deep inelastic fragments from the reaction nat Ag+340 MeV 40 Ar have been studied in coincidence. Charged particles (10 ≦ Z ≦ 32) were detected and identified in Z by means of a ΔE − E telescope, while the complementary fragments were detected in a one-dimensional, solid-state position-sensitive detector. Both in-plane and out-of-plane correlations were measured. The results confirm the binary nature of the deep inelastic process for this reaction. From the measured energies and angles of the fragments and the atomic number of one of the fragments, it was possible to determine the total mass loss due to the de-excitation of the fragments as well as the total evaporated charge at symmetry. An iterative procedure is discussed which enables one to determine the masses and kinetic energies of the fragments before evaporation, as well as the total number of particles evaporated by each fragment. The widths of the in-plane and out-of-plane correlations agree with the results of the iterative calculations, as do evaporation calculations which are based on the charge equilibrium model. The experimental results support the charge equilibrium model and indicate that thermal equilibrium is achieved between the fragments at fixed mass asymmetry.

Charged particles produced from the interaction of a 7.2 MeV/nucleon Kr beam and a natural Ag target have been studied. Fragments up to Z = 50 have been identified by means of a ΔE , E telescope. Kinetic energy distributions, charge distributions and angular distributions have been measured for the individual atomic numbers. The kinetic energy distributions show two components: a high energy “quasi-elastic” component, and a low energy or “relaxed” component close to the Coulomb energy for touching spheres. The charge distribution for this system is very broad and appears to peak at symmetry rather than at the Z of the projectile. The angular distributions for the relaxed component increase monotonically with decreasing angle and are all forward peaked in excess of 1/sinθ. These results are dramatically different from those obtained in Kr bombardments of heavier targets where rather narrow charge distributions and side peaked angular distributions have been observed. The behavior of the reaction Ag+Kr is strongly reminiscent of reactions induced by lighter projectiles. An interpretation of these data in terms of a diffusion process along the mass asymmetry coordinate is presented.

Protons andα-particles emitted in coincidence with a deep inelastic fragment produced in the reaction40Ar (280 MeV)+58Ni have been measured. From a detailed study of their in-plane angular distribution, it is shown that the bulk of the light charged particle emission can be attributed to a secondary evaporation process by the two primary deep inelastic fragments. A lowest estimate of the fragment spin (assuming total alignment perpendicular to the reaction plane) is obtained from the anisotropy of the out-of-plane angular distribution of theα-particles. For very asymmetric splitting, the heavy fragment spin estimate as obtained from theα-anisotropy measurement is consistent with the observed proton toα-particle multiplicity ratio. The results are in agreement with the hypothesis of a sticking configuration between two deformed nuclei.

Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.

Dramatic changes of fragment angular distributions over a large range of atomic numbers in the reactions induced by 14 N, 20 Ne, and 40 Ar on natural Ag targets are interpreted as evidence of a diffusion-controlled evolution of an intermediate complex along the mass asymmetry degree of freedom.

Atomic numbers and masses have been identified for the fragments (12

The collective flow measurements presented in this lecture have been performed with the DIOGENE electronic 4π-detector1 installed at the Saturne synchrotron in Saclay, which can deliver beams up to mass 40. In order to study the properties of dense (and hot) nuclear matter, it is required to measure nucleus-nucleus collisions involving a large number of nucleons That is the reason why we focused our experiment on asymmetric collisions,, with target nuclei heavier than the beam.

Experimental results concerning proton production in nuclear collisions, obtained at Saturne with the Diogene 4π facility, are compared with the predictions of a thermodynamical model, using collective velocity distributions combined with a statistical thermodynamics in local rest frames. Experimental differential cross sections for alpha + nucleus and Neon + nucleus central collisions at incident energies between 200 and 800 MeV per nucleon are well reproduced by the model, for an angular range 30–110 degrees in the laboratory system. Extracted values of the temperatures are compared with those given by other authors.

Angular distributions of cross section, and A y and A yy analysing powers were measured for polarised deuteron elastic scattering from 16 O at 200, 400 and 700 MeV. The data at 200 MeV bear evidence of the nuclear rainbow phenomenon while those at 400 and 700 MeV are reminiscent of the proton scattering results at equivalent energies. The data were analysed in terms of the optical model. The real central potential shape changes from an attractive Woods-Saxon form at 200 MeV to a wine-bottle-bottom form with a repulsive interior at 700 MeV. The total reaction cross sections deduced display a clear nuclear transparency effect in the present energy domain in agreement with predictions from the Glauber theory optical limit. Comparison with previous results for 40 Ca and 58 Ni targets is made.

Deep inelastic collisions have been studied in the reaction 40Ca + 64Ni at 182 MeV bombarding energy. It is clearly shown that provided the energies over the interaction barrier are similar, heavy and light systems show the same trends. The charge distributions and the total kinetic energy loss are shown to be related to the interaction time and are discussed in the framework of a diffusion model. The total cross section of the DIC process is compared with other exit channel cross sections.

Mean multiplicities of pi+ and pi- in 4He collisions with C, Cu, and Pb at 200, 600, and 800 MeV/u, and with C and Pb at 400 MeV/u have been measured using the large solid angle detector Diogene. The independence of pion multiplicity on projectile incident energy, target mass and proton multiplicity is studied in comparison with intra-nuclear cascade predictions. The discrepancy between experimental results and theory is pointed out and discussed.

The binary character of the deep inelastic collisions observed in the reaction 58 Ni + 40 Ar at 280 MeV has been investigated. Two major fragments were detected in coincidence. The light fragment was identified both in mass (by the time of flight technique) and charge (using a ΔE - E telescope). Within the experimental uncertainties, the hypothesis of a binary process has been verified. More than 80% of the events correspond to a reaction mechanism where, apart from light particles, only two major fragments are observed in the exit channel. The deviation from an exactly binary process leads to an indirect measurement of the number of particles evaporated by the excited fragments. The total mass of the particles emitted by the light fragment alone is deduced. The results are suggestive of equal temperature for both light and heavy fragments. Finally, the total number of particles evaporated is estimated. The emission of α-particles is invoked in order to consistently explain the data.

The least action principle is used to determine the semiclassical path in the penetration of a multidimensional fission barrier using the gap parameter as a dynamical variable. An increase in the gap parameter, the larger the deeper the penetration of the barrier is predicted.

Angular distributions of cross section, and A y and A yy analyzing powers were measured for polarized deuteron elastic scattering from 58 Ni at 200, 400 and 700 MeV, and 40 Ca at 700 MeV. Phenomenological potentials were obtained from an optical model analysis of the data. The total reaction cross sections deduced were compared to predictions from the Glauber theory optical limit.

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.

It is shown how one can take advantage of evaporated charged particles emitted by fully thermally equilibrated deep inelastic fragments to extract both spin and degree of alignment of these fragments. The investigated system is 40Ar(280 MeV) + 58Ni.