New Measurements of Charge-changing Cross Sections in Carbon and Hydrogen Targets above 2 GeV per Nucleon: Evidence for an Energy Dependence That May Strongly Affect Estimates of the Energy Dependence of Cosmic-Ray Diffusion in the Galaxy

We have recently measured the fragmentation of approximately 15 GeV per nucleon Si nuclei in CH2 and C targets and, by subtraction, H targets, at Brookhaven. The total-changing cross section for Si is larger than we measured earlier at approximately 1.3 GeV per nucleon. At the same time the partial cross sections for charge changes of 1 and 2 are approximately 20% to 50% smaller for all targets including H. An overall systematic behavior is observed for the ratio of the 15 GeV per nucleon to 1.3 GeV per nucleon partial cross sections as a function of the magnitude of the charge change. These results, when coupled with earlier measurements of the fragmentation of high energy O right arrow N and Si right arrow Al by the Siegen group (Hirzebruch et al. 1991), which also show a decrease in the partial cross sections for charge changes of 1 and 2 above 1 to 2 GeV per nucleon in H targets, have major implications for the energy dependence of the propagation of Galactic cosmic rays. This is because the B/C ratio is used to determine this dependence and the main channel for B production, C right arrow B, should also show a decreasing cross section with increasing energy according to the above argument. We will present this new cross-section data and examine their implications for the propagation of cosmic rays.