Approach to criticality in the fragmentation of xenon by 1<i>–</i>19 GeV protons

Differential cross sections for the emission of intermediate-mass fragments (3\ensuremath{\le}${Z}_{f}$\ensuremath{\le}14) at 48.5\ifmmode^\circ\else\textdegree\fi{} and 131.5\ifmmode^\circ\else\textdegree\fi{} in the interaction of xenon with 1--19 GeV protons have been measured. The excitation functions rise sharply with energy up to \ensuremath{\sim}10 GeV and then level off. The energy spectra were fitted with an expression based on the phase transition droplet model. Excellent fits with reasonable parameters were obtained for ${E}_{p}$\ensuremath{\ge}9 GeV. Below 6 GeV, the fits show an increasing contribution with decreasing energy from another mechanism, believed to be binary breakup. A droplet model fit to the cross sections ascribed to the multifragmentation component is able to reproduce the variation of the yields with both fragment mass and proton energy. The results are interpreted in terms of the phase diagram of nuclear matter.