R. Planeta

The BRAHMS experiment at RHIC.

The BRAHMS experiment at RHIC was conceived to pursue the understanding of nuclear matter under extreme conditions by detailed measurements of charged hadrons over the widest possible range of rapidity and transverse momentum. The experiment consists of two spectrometers with complementary charged hadron detection capabilities as well as a series of global detectors for event characterization. A series of tracking detectors, time-of-flight arms and Cherenkov detectors enables momentum determination and particle identification over a wide range of rapidity and transverse momentum. Technical details and performance results are presented for the various detector subsystems. The performance of the entire system working together is shown to meet the goals of the experiment.

Symmetric splitting of very light systems in the coalescence and reseparation model

Abstract The coalescence and reseparation model has been used to calculate trajectories of the 12 C + 40 Ca, 9 Be + 40 Ca and 6 Li + 40 Ca collisions which lead to symmetric splitting. A fusion-fission mechanism is suggested by the model. Comparison with experimental data locates the reaction angular momentum window in the region of superdeformed nuclei.

Fusion — Fission dynamics

Classical dynamical calculations of the heavy ion induced fission processes have been performed for the reactions40Ar+141Pr,20Ne+165Ho and12C+175Lu leading to the iridium like nucleus. As a result prescission lifetimes were obtained and compared with the experimental values. The comparison between the calculated and experimental lifetimes indicates that the one-body dissipation picture is much more relevant in describing the fusion-fission dynamics than the two-body one.

Complex fragment emission from the 3He+natAg system between 0.48 and 3.6 GeV☆☆☆

Abstract The emission of complex fragments (3⩽ Z ≲12) from reactions of 3 He with nat Ag has been studied at bombarding energies of E = 480, 900, 1800, 2700 and 3600 MeV. Between 900 and 1800 MeV slopes of the fragment kinetic energy spectra at backward angles undergo a change in character, becoming much flatter; in addition, the Coulomb peak is found to broaden significantly and shift to lower energies. Power-law fits to the fragment charge distributions result in decreasing values of the exponent τ up to a bombarding energy of 1800 MeV; at this value and beyond, a constant value of τ =2.1±0.1 is observed. Elemental cross sections at the highest energy are found to increase by approximately two orders of magnitude relative to data near 100 MeV. The data suggest a change in reaction mechanism between incident energies of 900 and 1800 MeV.

Rapidity dependent strangeness measurements in BRAHMS experiment at RHIC

Particle production of charged kaons in central Au+Au collisions at has been studied as a function of rapidity by the BRAHMS collaboration at RHIC. The kaon spectral shapes are described well by an exponential in transverse mass for the rapidity range of 0 ≤ yK ≤ 3.3 with smoothly decreasing inverse slopes as the rapidity increases. For the charged kaon to pion ratios, while there is no significant rapidity dependence for the K+/π+ ratio, the K−/π− ratio shows a significant decrease from y ≈ 1 towards higher rapidities. The systematics of K−/K+ and ratios in the measured rapidity range demonstrates a strongly correlated behaviour which can be described by thermal–statistical models.

Two-proton correlation functions for equilibrium and non-equilibrium emission

Abstract Two-proton correlation functions are compared for equilibrium and non-equilibrium emission processes investigated, respectively, in “reverse kinematics” for the reactions 129 XE+ 27 Al and 129 Xe+ 122 Sn at E A = 31 MeV and in “forward kinematics” for the reaction 14 N+ 197 Au at E A = 75 MeV . Observed differences in the shapes of the correlation functions are understood in terms of the different time scales for equilibrium and preequilibrium emission. Transverse and longitudinal correlation functions are very similar.

Gas chambers for identification of charged particles in 4π systems

Abstract Gas ionization chambers of a special shape adapted for 4π detector systems are presented. Different anode wire configurations are discussed for three working gases: Ar + methane(10%), isobutane, and tetrafluoromethane.

Excited state populations for equilibrium and preequilibrium emission

Abstract Populations of excited 5 Li and 6 Li fragments have been measured for the 3 He + Ag reaction at 200 MeV. At forward angles, fragments emitted via preequilibrium mechanisms display population probabilities that are consistent with emission temperatures of about 4 MeV, comparable to other measurements of preequilibrium processes. In contrasts, fragments emitted to backward angles display much smaller population probabilities consistent with emission temperatures of about 1 MeV. Such low temperatures are consistent with residue excitation energies predicted by molecular dynamics calculations.

Fragment production in the 197Au + 197Au reaction at 23A MeV

We present the current status of nuclear dynamics studies performed by the BREAKUP group with the 4π CHIMERA array, for the system 197Au + 197Au at 23A MeV.

Results from the BRAHMS experiment at RHIC

Results from the BRAHMS Collaboration for the inaugural physics run with the relativistic heavy ion collider (RHIC), Au + Au collisions at √sNN = 130 GeV in the late summer of 2000, and some results of the very first data from the summer of 2001 at √sNN = 200 GeV are presented. Here the main focus is on the determination of the pseudorapidity distribution of charged particles as a function of collision centrality and on the measurement of the antiproton to proton and the K− to K+ ratios as a function of rapidity. The pseudorapidity density at midrapidity reaches dN(ch)/dη = 553 ± 36 for the most central collisions (0–5%) at √sNN = 130 GeV; the corresponding number for a higher energy is dN(ch)/dη = 632 ± 36, demonstrating an increase in multiplicity of about 14%. The measured antiproton/proton ratios peak at midrapidity around N()/N(p) = 0.64 ± 0.06 and drop to 0.41 ± 0.04 at y ≈ 2 for √sNN = 130 GeV reactions; the K− to K+ ratios are 0.90 ± 0.06 (y ≈ 0) and 0.83 ± 0.1 (y ≈ 2.5).