Semi-inclusive proton and pion distributions from central Au+Au reactions at 11.6$A$ GeV/$c$ have been measured. The proton rapidity distribution shows significantly increased stopping compared to lighter systems, providing strong evidence for the formation of a state of matter with baryon density substantially greater than normal nuclear matter. Unlike reactions at this energy induced by lighter heavy ions, at low $m_t-m_0$ the proton invariant spectra deviate from a single exponential shape and become flatter, while ${\pi }^{-}$ spectra are found to rise faster than the ${\pi }^{+}$ spectra.

• Received 13 June 1997

DOI:https://doi.org/10.1103/PhysRevC.57.R466