Production of pions and light fragments in 0.8<i>A</i>GeV La+La collisions

Abstract

The spectra of pions and light fragments at laboratory angles from 10\ifmmode^\circ\else\textdegree\fi{} to 89\ifmmode^\circ\else\textdegree\fi{} were measured in 0.8A GeV La+La collisions. Event multiplicity was also measured to select central collisions. For inclusive data, the slope of the pion spectrum at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.=90\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$ for La+La is as steep as that for Ar+KCl while the slope of the proton spectrum at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.=90\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$ becomes less steep with increasing mass number of the colliding nuclei. Furthermore, the ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ yield is about half of the geometrical estimate while total nuclear charge yield agrees well. Since the yield ratio of ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ to total nuclear charge at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.=90\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$ is significantly larger for high multiplicity events than for inclusive data, it appears that pion absorption by spectator nucleons is important. An azimuthal correlation of charged particle emission was also observed, which is consistent with collective flow of nuclear matter. The coalescence relation between protons and composite fragments holds for inclusive data in La+La collisions.