Results of identified charged hadrons produced in Au+Au collisions at ${ \sqrt{ s_{ NN}}} = 130$ GeV as a function of centrality are discussed. The $<{ p_{ T}}>$ of protons and antiprotons is significantly larger than in p--p collisions at the same center of mass energy. Its scaling with the number of participant nucleons, an increase of $20 \pm 5%$ from peripheral to central, may be due to radial expansion. In a hydrodynamical picture a simultaneous fit of pions, kaons and protons is consistent with a radial flow velocity of $\beta_{ \rm{ Tsurface}} = 0.72 \pm 0.01$ and a temperature of $T = 122 \pm 4$ MeV for the 5% most central collisions. Dominant proton yields at ${ p_{ T}} > 1.5$ GeV/c and antiproton yields at ${ p_{ T}} > 1.8$ GeV/c may be explained by a combination of suppression of pion yields at high ${ p_{ T}}$ and the boost of low ${ p_{ T}}$ protons to high ${ p_{ T}}$ from radial flow.
Categories: nucl-ex