Baryon Stopping and Charged Particle Distributions in Central $Pb+Pb$ Collisions at 158 GeV per Nucleon

Net proton and negative hadron spectra for central $\mathrm{Pb}+\mathrm{Pb}$ collisions at 158 GeV per nucleon at the CERN Super Proton Synchrotron were measured and compared to spectra from lighter systems. Net baryon distributions were derived from those of net protons. Stopping (rapidity shift with respect to the beam) and mean transverse momentum $〈p_T〉$ of net baryons increase with system size. The rapidity density of negative hadrons scales with the number of participant nucleons for nuclear collisions, whereas their $〈p_T〉$ is independent of system size. The $〈p_T〉$ dependence upon particle mass and system size is consistent with larger transverse flow velocity at midrapidity for $\mathrm{Pb}+\mathrm{Pb}$ compared to $\mathrm{S}+\mathrm{S}$ central collisions.