arXiv subjects
Publications and source records attributed to J. Barrette.
We present proton and pion tranverse momentum spectra and rapidity distributions for Au+Au collisions at 10.8A GeV/c. The proton spectra exhibit collective transverse flow effects. Evidence of the influence of the Coulomb interaction from the fireball is found in the pion transverse momentum spectra. The data are compared with the predictions of the RQMD event generator.
Inclusive double differential multiplicities of deuterons, ^3H, ^3He, and ^4He measured by E877 for 11.5 A GeV/c Au+Au collisions at the AGS are presented. Light fragments at beam-rapidity are measured for the first time at AGS energies. Beam rapidity deuteron and ^4He yields and transverse slope parameters are found to be strongly dependent on impact parameter and the shape of the deuteron spectra is not consistent with that expected for a simple thermal distribution. The deuteron yields relative to proton yields are analyzed in terms of a simple coalescence model. While results indicate an increase in source size compared to collisions of lighter systems at the same energy, they are inconsistent with a simple coalescence model reflected by a rapidity dependence of the coalescence parameter B_d. A new approach utilizing an expanding thermalized source combined with a coalescence code is developed for studying deuteronformation in heavy-ion collisions. The strong dependence of deuteron yields on collective motion implies that deuteron yields relative to those of protons can be used for constraining source parameters.
We present new results from the analysis of the E877 data taking run in 1995. Anisotropy in the azimuthal distribution of produced pions, kaons(K^+, K^-), lambda and antiprotons in Au+Au collisions at 11.5A GeV, are investigated . The data are compared with the predictions of the RQMD v2.3 event generator.
Two-proton correlation functions have been measured in Si+Pb collisions at 14.6A GeV/c and Au+Au collisions at 11.5A GeV/c by the E814/E877 collaboration. Data are compared with predictions of the transport model RQMD and the source size is inferred from this comparison. Our analysis shows that, for both reactions, the characteristic size of the system at freeze-out exceeds the size of the projectile, suggesting that the fireball created in the collision has expanded. For Au+Au reactions, the observed centrality dependence of the two-proton correlation function implies that more central collisions lead to a larger source sizes.
Directed flow of deuterons, tritons, $^3$He, and $^4$He is studied in Au+Au collisions at a beam momentum of about 10.8 $A$ GeV/c. Flow of all particles is analyzed as a function of transverse momentum for different centralities of the collision. The directed flow signal, $v_1(p_t)$, is found to increase with particle mass. This mass dependence is strongest in the projectile rapidity region.
Results are presented of an analysis of proton and charged pion azimuthal distributions measured with respect to the reaction plane in Au + Au collisions at a beam momentum of about 11 AGeV/c. The azimuthal anisotropy is studied as a function of particle rapidity and transverse momentum for different centralities of the collisions. The triple differential (in rapidity, transverse momentum, and azimuthal angle) distributions are reconstructed. A comparison of the results with a previous analysis of charged particle and transverse energy flow as well as with model predictions is presented.
Two-particle correlation functions for positive and negative pions have been measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed using one- and three-dimensional correlation functions. From the results of the three-dimensional fit the phase space density of pions was calculated. It is consistent with local thermal equilibrium.
Experimental results and a detailed analysis are presented of the transverse energy and charged particle azimuthal distributions measured by the E877 collaboration for different centralities of Au+Au collisions at a beam momentum of 10.8 A GeV/c. The anisotropy of these distributions is studied with respect to the reaction plane reconstructed on an event-by-event basis using the transverse energy distribution measured by calorimeters. Results are corrected for the reaction plane resolution. For semicentral events we observe directed flow signals of up to ten percent. We observe a stronger anisotropy for slow charged particles. For both the charged particle and transverse energy distributions we observe a small but non zero elliptic anisotropy with the major axis pointing into the reaction plane. Combining the information on transverse energy and charged particle flow we obtain information on the flow of nucleons and pions. The data are compared to event generators and the need to introduce a mean field or nucleon-nucleon potential is discussed.
We present measurements of the pion transverse momentum (p_t) spectra in central Si-nucleus collisions in the rapidity range 2.0<y<5.0 for p_t down to and including p_t=0. The data exhibit an enhanced pion yield at low p_t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Delta-resonance abundance at freeze-out. The results are consistent with a direct measurement of the Delta-resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.
Event shapes for Au + Au collisions at 11.4 GeV/c per nucleon were studied over nearly the full solid angle with the E877 apparatus. The analysis was performed by Fourier expansion of azimuthal distributions of the transverse energy (E_T) measured in different pseudorapidity intervals. For semicentral collisions a pronounced event anisotropy is identified beyond that expected due to fluctuations in particle multiplicity. The signal decreases for peripheral and very central collisions. The amplitude of the flow signal reaches up to 7% of the mean E_T.