No Arabic abstract
The interplay of the effects of geometry and collective motion on d-$alpha$ correlation functions is investigated for central Xe+Au collisions at E/A=50 MeV. The data cannot be explained without collective motion, which could be partly along the beam axis. A semi-quantitative description of the data can be obtained using a Monte-Carlo model, where thermal emission is superimposed on collective motion. Both the emission volume and the competition between the thermal and collective motion influence significantly the shape of the correlation function, motivating new strategies for extending intensity interferometry studies to massive particles.
Multifragment disintegrations, measured for central Au + Au collisions at E/A = 35 MeV, are analyzed with the Statistical Multifragmentation Model. Charge distributions, mean fragment energies, and two-fragment correlation functions are well reproduced by the statistical breakup of a large, diluted and thermalized system slightly above the multifragmentation threshold.
The signals theoretically predicted for the occurrence of a critical behavior (conditional moments of charge distributions, Campi scatter plot, fluctuations of the size of the largest fragment, power law in the charge distribution, intermittency) have been found for peripheral events in the reaction Au+Au at 35 MeV/u. The same signals have been studied with a dynamical model which foresees phase transition, like the Classical Molecular Dynamics.
A systematic study of energy spectra for light particles emitted at midrapidity from Au+Au collisions at E=0.25-1.15 A GeV reveals a significant non-thermal component consistent with a collective radial flow. This component is evaluated as a function of bombarding energy and event centrality. Comparisons to Quantum Molecular Dynamics (QMD) and Boltzmann-Uehling-Uhlenbeck (BUU) models are made for different equations of state.
Multifragment events resulting from peripheral Au + Au collisions at 35 MeV/nucleon are analysed in terms of critical behavior. The analysis of most of criticality signals proposed so far (conditional moments of charge distributions, Campi scatter plot, fluctuations of the size of the largest fragment, intermittency analysis) is consistent with the occurrence of a critical behavior of the system.
Recently, multiparticle-correlation measurements of relativistic $p/d/^3$He$+$Au, $p$$+$Pb, and even $p$$+$$p$ collisions have shown surprising collective signatures. Here we present beam-energy-scan measurements of 2-, 4-, and 6-particle angular correlations in $d$$+$Au collisions at $sqrt{s_{_{NN}}}$=200, 62.4, 39, and 19.6 GeV. We also present measurements of 2- and 4-particle angular correlations in $p$$+$Au collisions at $sqrt{s_{_{NN}}}$=200 GeV. We find the 4-particle cumulant to be real-valued for $d$$+$Au collisions at all four energies. We also find that the 4-particle cumulant in $p$$+$Au has the opposite sign as that in $d$$+$Au, indicating that the correlations are geometrical and therefore collective in origin. Further we find that the 6-particle cumulant agrees with the 4-particle cumulant in $d$$+$Au collisions at 200 GeV, which indicates that nonflow effects are subdominant and provides strong evidence of collectivity.