Projectile energy degradation at 14. 5 GeV/u

The generation of states of high energy density hinges on the question of nuclear stopping or, in other words, on the rapidity lost by the projectile as it ploughs through the target. Recent data have shown ( 1-2 ) that, at 10 and 14.5 GeV/u, the total neutral (E/sup 0//sub TOT/) and transverse energy ( ET) distributions can be used to infer complete stopping, as measured by the inability of targets heavier than Cu to yield additional neutral energy. An alternative measurement of projectile stopping would rely on the absence of significant residual projectile energy along its direction of motion. We present experimental evidence showing that the flow of forward energy is a valuable probe of nuclear stopping and that, at 14.5 GeV/u, the projectile energy is completely degraded for central collisions in heavy targets. The forward energy observed is shown to be adequately reproduced by simple geometrical calculations. The correlation of the forward energy with E/sup 0//sub TOT/, will be shown to provide information on the number of projectile participant nucleons. 5 refs., 2 figs.