Transverse momentum distributions of hadrons produced in gold+gold collisions at 130 GeV measured by the PHENIX experiment at RHIC BNL

The transverse momentum (p_t) distributions of hadrons produced in Au+Au collisions at 130 GeV are measured at midrapidity, from the most central to the most peripheral collisions, by the PHENIX Experiment at RHIC BNL. The spectra are measured by highly segmented Time-of-Flight, Pad Chamber, and Drift Chamber detectors. The events are triggered, and the event centrality is determined by the Beam-Beam Counters and Zero Degree Calorimeters.; Already after the first year of RHIC running, the data show both hard and soft physics. A feature unpredicted by perturbative QCD calculations is the crossing of proton and pion spectra at 1.5–2 GeV/c in p _t. A plausible explanation is the jet-quenching of high pt pions and the broadening of low p_t (anti)protons due to strong radial expansion.; The pion yield varies linearly with the number of participant nucleons. The kaon and (anti)proton yields may also depend on the number of nucleon-nucleon binary collisions. The total hadron yield agrees with published results. In central collisions, the average initial energy density is 4.9 GeV/fm 3, 70% higher than in Pb+Pb collisions at CERN. The average transverse momentum increases with participant number, indicative of radial expansion.; A hydrodynamics parameterization is fit simultaneously to the hadron spectra in a pt range that minimizes contributions from hard processes. The resonance and weak decay contribution is excluded in the fit to the pion spectra. In central events, the radial velocity of the expanding surface is 0.70 ± 0.01 c, with hadrons decoupling at a temperature of 121 ± 4 MeV. A hydrodynamics model with an equation of state that simulates a mixed phase transition between a hadron gas and a relativistic gas of quarks and gluons describes the hadron spectra.; The extrapolated spectrum from radial flow contributions is compared to the charged spectrum measured out to 5 GeV/c. The transition region between soft and hard processes is 2.5–3 GeV/c in p_t. In order to measure jet-quenching the spectra need to be measured for p_t > 3 GeV/c. At CERN SPS energies, the high pt pion spectra are described by hydrodynamics and need to be measured up to 5 GeV/c in p_t.; The radial expansion is stronger than at CERN, yet the particle-emitting sources are the same size. This is in contradiction to hydrodynamic predictions and further analysis is necessary in order to understand this discrepancy.