Baryon-Baryon correlations at small relative momentum in Neon- and Argon-nucleus collisions betweenE/A=200 and 1000 MeV

Abstract

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 targetprojectile 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. PACS: 25.70. -z Two-particle correlations at small relative momentum allow to determine the size (and the lifetime) of the emitting source in a quite direct way. It is clear that two particles close in velocity are sensitive to the space-time extension of the emitting source through Coulomb and nuclear interactions, and also through statistical effects, according to whether they are fermions or bosons. The method of proton, composite particle or pion correlations is well suited for the study of heavy ion collisions where many efforts are still to be made to investigate the interacting region. Interesting results have already been obtained showing differences between collisions at very different [2][3][4][5] for the most energetic particles; but it is also possible that the emission time intervals are smaller for these particles, leading to the interpretation of smaller sources. When the correlation is analyzed for different orientations of the relative momentum [6], it has been found that the most energetic particles are emitted from a short-lived source of the size of the compound-nucleus, while the low-energy protons appear to be emitted from a source considerably larger than the compound-nucleus. At CERN-SPS energies [7], surprisingly large transverse sizes have been found for the source of mid-rapidity particles but the interpretation is not yet clear.In the intermediate energy range MeV per nucleon), many correlation results seem to confirm the validity of the participant-spectator model and the existence of a fireball; the source sizes increase with increasing target-projectile mass [8] and centrality of the collision [9]. Moreover, many zr -z~ correlation results [10, 11] indicate that the source sizes are smaller for the higher energy particles (but emission time effects cannot be excluded in this case too).The two-particle correlation method is intrinsically sensitive to final-state interactions and the results are significant of the latest stage of deexcitation of the fireball when the collisions between parti...