Subthreshold antiproton,K−,K+, and energetic-pion production in relativistic nucleus-nucleus collisions

We present a measurement of subthreshold antiproton, kaon, and energetic pion production at 0° for the reactions ${}_{}{}^{28}{}_{}{}^{}$Si${+}^{28}$Si at 2.0 GeV/nucleon ($E_{\mathrm{available}/\mathrm{A}=0.82\mathrm{}}$ GeV) and 1.65 GeV/nucleon ($E_{\mathrm{available}/\mathrm{A}=0.70\mathrm{}}$ GeV), and for ${}_{}{}^{20}{}_{}{}^{}$Ne+NaF at 2.0 GeV/nucleon. For a given reaction, the particle yields, plotted as a function of the required excitation energy, exhibit a scaling behavior independent of particle species. Implications for collectivity and a common production mechanism are discussed.