Measurement of pions and light fragments in 0.8 GeV/nucleon La + La collisions

Using the upgraded Bevalac, the authors have measured inclusive spectra of light fragments at theta/sub lab/ = 150, 200, 300, 400, 600, and 800 and negative pions at theta/sub lab/ = 600, which corresponds approximately to 900 in the c.m., in 0.8 GeV/nucleon 57139La + 57139La collisions. The Lorentz invariant differential cross sections for protons in the La + La collisions show simple exponential spectra at c.m. 900, exp(-E/sub k//E0), whereas for lighter-mass collisions the spectrum deviates substantially from the exponential in the low-energy region, showing a shoulder-arm shape. Compared to the Ar + KCl data, the value of E0 is slightly larger for the La + La collisions. It is likely that the simple exponential shape is due to a greater degree of equilibration for the La + La collisions. The momentum distribution of deuterons at theta/sub lab/ = 150 is plotted together with the Ar + KCl data, which is multiplied by a factor of 6. Deuteron spectra in La + La at theta/sub lab/ = 150 show an enhancement at approx.2GeV/c and also at less than or equal to0.7GeV/c. Such behavior is not consistent with a single-source model, but can be understood in terms of a three-fireball model