Mid-rapidity protons in 158A·GeV Pb+Pb collisions

Proton distributions at mid-rapidity (2 ≤ y ≤ 3) have been measured for 158A·GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. From baryon number conservation and by comparing the experimentally measured dNdy distribution with the transport model RQMD, we conclude that a rather high degree of nuclear stopping has been reached for the truly heavy-ion collisions at these energies. Transverse mass distributions exhibit characteristically thermal shapes and the slope parameters increase with the mass of the colliding system.