Development of solenoid-spectrometer for electron-positron coincidence experiment. To search for e⁺e^- pair production by an irradiation of 2 MeV β⁺ to Th foil target

In 1983, at GSI in Germany, the first observation was made on positrons excited from Dirac sea by heavy ion collisions with heavy element targets. In addition, an unexpected finding was accompanied i.e., the appearance of the sharp positron peak above the wide positron bump mentioned above. On this positron peak, although there continued extensive investigations until the end of 1980's, a clear explanation couldn't be achieved. At INS, Univ. of Tokyo at Tanashi, this positron issue had been also studied mainly with an air core spectrometer. The last data at Tanashi was strongly argued whether it should be confirmed at Tsukuba where the Institute moved, after reorganization with previous KEK. The experiment team decided to pursuit the theme with a newly prepared solenoid spectrometer. This report concerns the result of this spectrometer development, and the experiment itself couldn't reach to the final goal. (author)