Production of pions and light fragments at large angles in high-energy nuclear collisions

Abstract

Inclusive cross sections for production of ${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{\ensuremath{-}}$, $p$, $d$, $^{3}\mathrm{H}$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ have been measured at laboratory angles from 10\ifmmode^\circ\else\textdegree\fi{} to 145\ifmmode^\circ\else\textdegree\fi{} in nuclear collisions of Ne + Naf, Ne + Cu, and Ne + Pb at 400 MeV/nucleon, C + C, C + Pb, Ne + NaF, Ne + Cu, Ne + Pb, Ar + KCl, and Ar + Pb at 800 MeV/nucleon, and Ne + NaF and Ne + Pb at 2.1 GeV/nucleon. The production of light fragments in proton induced collisions at beam energies of 800 MeV and 2.1 GeV has also been measured in order to allow us to compare these processes. For equal-mass nuclear collisions the total integrated yields of nuclear charges are well explained by a simple participant-spectator model. For 800 MeV/nucleon beams the energy spectra of protons at c.m. 90\ifmmode^\circ\else\textdegree\fi{} are characterized by a "shoulder-arm" type of spectrum shape with an exponential falloff at high energies, whereas those of pions are of a simple exponential type. The inverse of the exponential slope, ${E}_{0}$, for protons is systematically larger than that for pions. This value of ${E}_{0}$ is larger for heavier-mass projectiles and targets. It also increases monotonically with the beam energy. The angular anisotropy of protons is larger than that of pions. The yield ratio of ${\ensuremath{\pi}}^{\ensuremath{-}}$ to total nuclear charge goes up with the beam energy, whereas the yields of composite fragments decrease. The ratio of low-energy ${\ensuremath{\pi}}^{\ensuremath{-}}$ to ${\ensuremath{\pi}}^{+}$, as well as that of $^{3}\mathrm{H}$ to $^{3}\mathrm{He}$, is larger than the neutron to proton ratio of the system. The spectrum shape of the composite fragments with mass number $A$ is explained very well by the $A\mathrm{th}$ power of the observed proton spectra. The sizes of the interaction region are evaluated from the observed coalescence coefficients. The radius obtained is typically 3-4 fm. The yield ratio of composite fragments to protons strongly depends on the projectile and target masses and the beam energy, but not on the emission angle of the fragments. These results are compared with currently available theoretical models.NUCLEAR REACTIONS Ne + NaF, Ne + Cu, Ne + Pb, $\frac{E}{A}=400$ MeV/nucleon; C + C, C + Pb, Ne + NaF, Ne + Cu, Ne + Pb, Ar + KCl, Ar + Pb, $\frac{E}{A}=800$ MeV/nucleon; Ne + NaF, Ne + Pb, $\frac{E}{A}=2100$ MeV/nucleon; $p$ + C, $p$+ NaF, $p$ + KCl, $p$ + Cu, $p$ + Pb, $E=800$ MeV; $p$ + C, $p$ + NaF, $p$ + KCl, $p$ + Cu, $p$ + Pb, $E=2100$ MeV; measured $\ensuremath{\sigma}(p,\ensuremath{\theta})$ for ${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{\ensuremath{-}}$, $p$, $d$, $^{3}\mathrm{H}$, $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$.