Transverse energy, charged particle pseudorapidity distributions and photon transverse momentum spectra have been studied as a function of the number of participants (\(N_{part}\)) and the number of ...binary nucleon-nucleon collisions (\(N_{coll}\)) in 158\(\cdot A\) GeV Pb+Pb collisions over a wide impact parameter range. A scaling of the transverse energy pseudorapidity density at midrapidity as \(\sim N_{part}^{1.08 \pm 0.06}\) and \(\sim N_{coll}^{0.83 \pm 0.05}\) is observed. For the charged particle pseudorapidity density at midrapidity we find a scaling as \(\sim N_{part}^{1.07 \pm 0.04}\) and \(\sim N_{coll}^{0.82 \pm 0.03}\). This faster than linear scaling with \(N_{part}\) indicates a violation of the naive Wounded Nucleon Model.
Direct thermal photons in the
p
T
range of 0–5 GeV/c are expected to provide a sensitive probe of the hot dense matter formed in the early stage of relativistic heavy ion collisions. The production ...of single photons in 200 A GeV S + Au reactions has been investigated using the 3800 element Pbglass calorimeter of CERN experiment WA80. Neutral
π
0 and η cross sections have been measured via their two-photon decay branch yields. In a first analysis of the WA80 results, a slight excess photon yield above that which may be accounted for by hadronic decays was observed for central collisions. A report on the status of the reanalysis of this data is presented.
J/psi production in p+p collisions at sqrt(s)=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over a rapidity range of -2.2<y<2.2 and a transverse ...momentum range of 0<pT<9 GeV/c. The size of the present data set allows a detailed measurement of both the pT and the rapidity distributions and is sufficient to constrain production models. The total cross section times the branching ratio is Bllsigma pp J/psi =178{+-}3stat{+-}53sys{+-}18norm nb.
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC)has measured J/{psi} production for rapidities -2.2<y<2.2 in Au+Au collisions at {radical}(s{sub NN})=200 GeV. The J/{psi} ...invariant yield and nuclear modification factor R{sub AA} as a function of centrality, transverse momentum, and rapidity are reported. A suppression of J/{psi} relative to binary collision scaling of proton-proton reaction yields is observed. Models which describe the lower energy J/{psi} data at the CERN Super Proton Synchrotron invoking only J/psi destruction based on the local medium density predicta significantly larger suppression at RHIC and more suppression at midrapidity than at forward rapidity. Both trends are contradicted by our data.
The dependence of transverse momentum spectra of neutral pions and {eta} mesons with p{sub T}<16 GeV/c and p{sub T}<12 GeV/c, respectively, on the centrality of the collision has been measured at ...midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) in d+Au collisions at {radical}s{sub NN}=200 GeV. The measured yields are compared to those in p+p collisions at the same {radical}s{sub NN} scaled by the number of underlying nucleon-nucleon collisions in d+Au. At all centralities, the yield ratios show no suppression, in contrast to the strong suppression seen for central Au+Au collisions at RHIC. Only a weak pT and centrality dependence can be observed.
Correlations between p and {anti p} at transverse momenta typical of enhanced baryon production in Au + Au collisions are reported. The PHENIX experiment has measured same and opposite sign baryon ...pairs in Au + Au collisions at {radical}{ovr S{sub NN}} = 200 GeV. Correlated production of proton and {anti p} with the trigger particle from the range 2.5 < p{sub T} < 4.0 GeV/c and the associated particle with 1.8 < p{sub T} < 2.5 GeV/c is observed to be nearly independent of the centrality of the collisions. Same sign pairs show no correlation at any centrality. The conditional yield of mesons triggered by baryons (and anti-baryons) and mesons in the same p{sub T} range rises with increasing centrality, except for the most central collisions, where baryons show a significantly smaller number of associated mesons. These data are consistent with a picture in which hard scattered partons produce correlated p and {anti p} in the p{sub T} region of the baryon excess.
Correlations between p and {bar p} at transverse momenta typical of enhanced baryon production in Au + Au collisions are reported. The PHENIX experiment has measured same and opposite sign baryon ...pairs in Au + Au collisions at {radical}s{sub NN} = 200 GeV. Correlated production of p and {bar p} with the trigger particle from the range 2.5<p{sub T}<4.0 GeV/c and the associated particle with 1.8<pT<2.5 GeV/c is observed to be nearly independent of the centrality of the collisions. Same sign pairs show no correlation at any centrality. The conditional yield of mesons triggered by baryons (and anti-baryons) and mesons in the same pT range rises with increasing centrality, except for the most central collisions, where baryons show a significantly smaller number of associated mesons. These data are consistent with a picture in which hard scattered partons produce correlated p and {bar p} in the p{sub T} region of the baryon excess.