  Transverse momentum spectra and yields of hadrons are measured by the PHENIX
collaboration in Au + Au collisions at sqrt(s_NN) = 130 GeV at the Relativistic
Heavy Ion Collider (RHIC). The time-of-flight resolution allows identification
of pions to transverse momenta of 2 GeV/c and protons and antiprotons to 4
GeV/c. The yield of pions rises approximately linearly with the number of
nucleons participating in the collision, while the number of kaons, protons,
and antiprotons increases more rapidly. The shape of the momentum distribution
changes between peripheral and central collisions. Simultaneous analysis of all
the p_T spectra indicates radial collective expansion, consistent with
predictions of hydrodynamic models. Hydrodynamic analysis of the spectra shows
that the expansion velocity increases with collision centrality and collision
energy. This expansion boosts the particle momenta, causing the yield from soft
processes to exceed that for hard to large transverse momentum, perhaps as
large as 3 GeV/c.
