We review the main results obtained by the BRAHMS Collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A ...particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so-called quark–gluon plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e., the proposed color glass condensate.
Scanning the phases of QCD with BRAHMS Murray, Michael; Collaboration, the BRAHMS
Journal of Physics G: Nuclear and Particle Physics,
08/2004, Letnik:
30, Številka:
8
Journal Article, Conference Proceeding
A deep level transient spectroscopy (DLTS) study of electrically active defects in electron irradiated silicon detectors has been performed. Two types of materials have been studied and compared: ...carbon-lean magnetic Czochralski (MCZ-) Si, and high purity, diffusion oxygenated float-zone (DOFZ-) Si. In both materials we observed an earlier reported shift in position of peaks associated with the divacancy (V2) at 250-325 deg C, indicating a gradual transition from V2 to the divacancy-oxygen complex (V2O). Heat treatments at higher temperatures reveal a difference in annealing behaviour of defects in DOFZ- and MCZ-Si. It is observed that VO and V2O anneal with a higher rate in DOFZ-Si. The appearance of a hydrogen related level only in the DOFZ-Si reveals a small presence of H and it is suggested that the difference in annealing behaviour is due to defect interaction with H in the DOFZ-Si. Our findings also suggest that dissociation may be a main mechanism for the annealing of V2O in MCZ-Si.
In this work the thermal kinetics of the transformation from the divacancy (V{sub 2}) to the divacancy-oxygen (V{sub 2}O) complex has been studied in detail, and activation energies (E{sub a}), have ...been obtained. Diffusion oxygenated float-zone silicon (DOFZ-Si) samples of n-type with a doping of 5x10{sup 12} cm{sup -3} and oxygen content of (2-3)x10{sup 17} cm{sup -3} have been irradiated with 15 MeV electrons. Isothermal annealing studies of electrically active defects have been performed by means of deep-level transient spectroscopy. Heat treatments at temperatures in the range 205 deg. C-285 deg. C have all shown a shift in the singly negative and doubly negative divacancy levels, due to the annealing of V{sub 2} and the formation of V{sub 2}O. By studying the temperature-dependent rate of this process which exhibits first order kinetics, it has been found that both the annealing V{sub 2} and the formation of V{sub 2}O have activation energies of {approx_equal}1.3 eV. This value is ascribed to migration of V{sub 2}, and the results favor strongly a model where V{sub 2} is trapped by interstitial oxygen atoms during migration. In addition, the process takes place with a high efficiency since the loss of V{sub 2} and the growth of V{sub 2}O display a close one-to-one proportionality. Finally, it has been found that the diffusivity pre-exponential factor, D{sub V{sub 2}}{sup 0}, for V{sub 2} is in the range 3{+-}1.5x10{sup -3} cm{sup 2}/s, which agrees well with a simple theoretical model of V{sub 2} diffusion in Si.
Charged-particle pseudorapidity densities are presented for the d + Au reaction at sqrts(NN) = 200 GeV with -4.2 < or = eta < or = 4.2. The results, from the BRAHMS experiment at BNL Relativistic ...Heavy-Ion Collider, are shown for minimum-bias events and 0%-30%, 30%-60%, and 60%-80% centrality classes. Models incorporating both soft physics and hard, perturbative QCD-based scattering physics agree well with the experimental results. The data do not support predictions based on strong-coupling, semiclassical QCD. In the deuteron-fragmentation region the central 200 GeV data show behavior similar to full-overlap d+Au results at sqrts(NN) = 19.4 GeV.
The BRAHMS experiment at RHIC has measured pions, kaons and protons and their antiparticles over a wide range of rapidity and transverse momenta. Au+Au collisions, d+Au and p+p interactions have been ...studied. From the net-proton rapidity distribution a stopping power of 73% can be deduced for central Au+Au collisions. The rapidity distributions of produced particles exhibit Gaussian shapes. At midrapidity the nuclear modification factor for central Au+Au collisions shows a strong pion suppression at intermediate transverse momenta; a suppression which is even stronger at forward rapidities. The nuclear modification factor for d+Au changes from a Cronin-like enhancement of charged hadrons at midrapidity to a suppression at forward rapidities.
After low dose electron irradiation, annealing kinetics of divacancy-oxygen (V{sub 2}O) and vacancy-oxygen (VO) complexes in carbon-lean n-type magnetic Czochralski (MCZ) and diffusion-oxygenated ...float-zone (DOFZ) Si samples has been studied in detail. The samples were of n type with a phosphorus doping concentration in the 10{sup 12} cm{sup -3} range, and the analysis was conducted by means of deep-level transient spectroscopy (DLTS). An exponential decrease in the V{sub 2}O concentration with time during isothermal annealing at temperatures in the range 275-355 deg. C has been observed. The activation energy for the V{sub 2}O annealing is found to be 2.02{+-}0.12 eV, with a preexponential factor in the 10{sup 13} s{sup -1} range, which strongly suggests that dissociation of V{sub 2}O is the dominating mechanism. The binding energy of the vacancy to the V{sub 2}O complex has been estimated as {approx}1.7 eV. An increase in the VO concentration is observed in the initial phase of the V{sub 2}O annealing, which is supportive of V{sub 2}O dissociation through the reaction V{sub 2}O{yields}VO+V. After the initial increase, a close to first order decrease in the VO concentration is observed, consistent with that VO mainly anneals by migration and trapping at oxygen interstitial sites, similarly to what has been reported in previous high-dose studies using infrared spectroscopy. The vacancy-oxygen-hydrogen complex (VOH) is formed after long time annealing. The formation of VOH is followed by a decrease at the same rate as VO, and it is suggested that VOH dissociates (VOH{yields}VO+H). The experimental data have been compared with kinetic simulations and show good agreement with a model where the main processes are dissociation of VO and V{sub 2}O, migration and subsequent trapping of VO ultimately giving rise to the electrically inactive vacancy-dioxygen pair (VO{sub 2}) and interactions involving atomic hydrogen.
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