R. K. Choudhury

J/psi production in Au-Au collisions at root s(NN)=200 GeV

First results on charm quarkonia production in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The yield of J/Psis measured in the PHENIX experiment via electron-positron decay pairs at mid-rapidity for Au-Au reactions at sqrt(s_NN) = 200 GeV are analyzed as a function of collision centrality. For this analysis we have studied 49.3 million minimum bias Au-Au reactions. We present the J/Psi invariant yield dN/dy for peripheral and mid-central reactions. For the most central collisions where we observe no signal above background, we quote 90% confidence level upper limits. We compare these results with our J/Psi measurement from proton-proton reactions at the same energy. We find that our measurements are not consistent with models that predict strong enhancement relative to binary collision scaling.

Evidence for large angular momentum induced deformations of 59Cu

Abstract The α -particle spectra observed in coincidence with evaporation residues of 59 Cu nuclei produced in the fusion of 214 MeV 32 S with 27 Al deviate at both high and low particle energies from the spectra calculated for spherical nuclei. The observed differences suggest large angular momentum induced deformations comparable to those predicted by rotating liquid drop model calculations.

Linear momentum and angular momentum transfer in the reactions of O 16 with Sm 154

From coincidence measurements between projectile-like fragments or heavy residues and their associated ..gamma.. rays, the angular momentum transfers for a variety of incomplete fusion reactions of 180 and 310 MeV /sup 16/O with /sup 154/Sm have been derived. At the higher energy, the correlation between angular momentum transfer and linear momentum transfer has been obtained over the entire range of linear momentum transfer. A comparison of the data with calculations of both the sum-rule and geometric overlap models indicates that each makes reasonable predictions of the observed trend even though the assumptions of the models are quite different, and very different initial partial waves are predicted to contribute to particular reaction channels. This results primarily from prescriptions relating fractional mass transfer to fractional angular momentum transfer. The reconstruction of the initial partial wave distributions from correlated measurements of linear momentum and angular momentum transfers is addressed. Comparisons are also made with more recent model calculations which focus on nucleon-nucleon scattering as the mechanism of momentum transfer.

The reactions of 12C with 12C AT 293 MeV

Abstract Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1−9 produced in the reactions of 12 C on 12 C. A total reaction cross section 1170 −100 +170 mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L crit for fusion of 10ħ in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.

Momentum widths in the fragmentation of 32 MeV/u /sup 10/B

Momentum widths of fragments produced in the reactions of 320 MeV /sup 10/B with /sup 181/Ta have been measured. At forward angles the energy spectra of light particles (Z = 1,2) exhibit energy peaks characterized by a reduced momentum with sigma/sub 0/ = 54 MeV/c, which is well below the values near 85 MeV/c observed in the reactions of 43 MeV/u /sup 20/Ne with /sup 181/Ta and in reactions induced by relativistic heavy ions. These results suggest a rapid increase in momentum widths, or apparent temperature, in the 32 to 43 MeV/u range.