COMPARISON OF 20 EXCLUSIVE REACTIONS AT LARGE T

We report a study of 20 exclusive reactions measured at the AGS at 5.9 GeV/c incident momentum, 90-degrees center of mass. This experiment c onfirms the strong quark flow dependence of two-body hadron-hadron sca ttering at large angle. At 9.9 GeV/c an upper limit had been set for t he ratio of cross sections for (ppBAR --> ppBAR)/(pp --> pp) at 90-deg rees c.m., with the ratio less than 4%. The present experiment was per formed at lower energy to gain sensitivity, but was still within the f ixed angle scaling region. A ratio R(ppBAR/pp) almost-equal-to 1/40 wa s measured at 5.9 GeV/c, 90-degrees c.m. in comparison to a ratio near 1.7 for small angle scattering. In addition, many other reactions wer e measured, often for the first time at 90-degrees c.m. in the scaling region, using beams of pi+/-, K+/-, p, and pBAR on a hydrogen target. There are similar large differences in cross sections for other react ions: R(K-p --> pi+SIGMA-/K-p --> pi-SIGMA+) almost-equal-to 1/12, for example. The relative magnitudes of the different cross sections are consistent with the dominance of quark interchange in these 90-degrees reactions, and indicate that pure gluon exchange and quark-antiquark annihilation diagrams are much less important. The angular dependence of several elastic cross sections and the energy dependence at a fixed angle of many of the reactions are also presented.