34 v 1 2 5 O ct 2 00 2 1 Mid - rapidity π ± , K ± , and p spectra and particle ratios from STAR

Results are presented on π ± , K ± , and p transverse mass spectra and particle multiplic-ity ratios at mid-rapidity in Au+Au collisions at √ s NN =130 and 200 GeV and in p+p collisions at √ s=200 GeV. Comparisons are made to results from lower energies. The bulk properties of the collision inferred from these results are discussed. New states in which the nucleon mass vanishes or quarks and gluons are deconfined have been predicted to exist at high densities over an extended volume [ 1, 2]. Such states may be created in relativistic heavy-ion collisions [ 1, 2]. Pions, kaons, and antiprotons are abundantly produced particles in relativistic heavy-ion collisions, reflecting the bulk properties of the collision: the yield of pions reflects on total entropy; kaons carry a significant fraction of the total strangeness produced; and the antiproton yield is a measure of baryon production. Measurements of these particles thus provide diagnostics to possible formation of the predicted new states [ 3, 4]. We present mid-rapidity transverse mass (m ⊥) spectra of charged pions (π ±), charged kaons (K ±), and antiproton (p) in Au+Au collisions at RHIC. We study spectral shapes in the picture of collective transverse radial flow and production of kaons and antiprotons relative to that of pions. We investigate the systematics of these results with respect to the collision centrality and in the context of results from lower energies to search for systematic changes which could result from possible changes in the collision dynamics. The data presented here are from minimum bias Au+Au collisions at nucleon-nucleon center-of-mass energy of √ s NN =130 and 200 GeV and p+p collisions at √ s=200 GeV by the STAR experiment [ 5]. Tracks were reconstructed in the STAR Time Projection Chamber (TPC). The magnetic field was 0.25 and 0.5 Tesla for the 130 and 200 GeV data, respectively. The primary vertex of the interaction was found by fitting the tracks to a common point of origin. Tracks used in the analysis were required to come from within 3 cm of the primary vertex. Corrections were made for the energy loss of particles in the detector material. Particles were identified by measuring the specific energy loss (dE/dx) of charged particles in the TPC gas. The dE/dx resolution was estimated to be 11% which imposed upper momentum limits on the identified particle spectra. Corrections were applied to account …