MID-RAPIDITY PROTONS IN 158A-CENTER-DOT-GEV PB+PB COLLISIONS

Proton distributions at mid-rapidity (2 less than or equal to y less t han or equal to 3) have been measured for 158A . GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. From baryon numb er conservation and by comparing the experimentally measured dN/dy dis tribution with the transport model RQMD, we conclude that a rather hig h degree of nuclear stopping has been reached for the truly heavy-ion collisions at these energies. Transverse mass distributions exhibit ch aracteristically thermal shapes and the slope parameters increase with the mass of the colliding system.