KEK (National Laboratory for High Energy Physics) annual report, 1986

The year 1986 has become an unforgettable year in the KEK history. In the predawn hours of November 19, 1986, the first large angle Bhabha scattering at the world highest energy of 48 GeV was observed at the TRISTAN electron-positron colliding beam complex. The first event was observed by a detector VENUS which is one of the three major detectors of TRISTAN. By the end of this fiscal year, 25 hadronlike events in total were observed by VENUS and AMY. There are also the TOPAZ using an improved TPC detector and the SHIP searching for highly ionizing particles. The 12 GeV proton synchrotron is now one of only a few proton accelerators in this energy range in the world. Unique and important experiments in the field of hadron spectroscopy and intermediate energy nuclear physics have been performed. The 500 MeV booster synchrotron has been used for the experiments on the crystalline structure of a high Tc superconductor, the measurement of muonic X-ray and the proton beam therapy of cancer. The Photon Factory was operated for 3,000 hours in 1986, and the beam lifetime of 20 hours with a 200 mA beam current was attained. The research activities in various departments are reported in detail. (Kako, I.)