ELASTIC BACKWARD SCATTERING OF PIONS AND KAONS

The elastic scattering of gp+ mesons by protons near 180° has been measured at 2.85, 3.30, and 3.55 GeV/c, that of π- mesons at 3.30 and 3..55 GeV/c, and that of K+ and K- mesons at 3.55 GeV/c. Steeply rising backward peaks are observed at all energies for π+p scattering, whereas the π-1p angular distributions are not as steep. K+p elastic scattering also shows a backward peak. No backward K-p elastic scattering event was found. The upper limit (90% confidence) for the K-p differential cross section is twelve times smaller than the corresponding K+p cross section. The behaviour of the differential cross section close to 180° can be explained using direct channel resonances. The large ratio of the K+p to K-p cross section can be understood in terms of baryon exchange. © 1969.