The PIBETA Spectrometer for Studying Rare and Forbidden Decays of Muons and Pions

摘要

The construction and characteristics of the PIBETA spectrometer are described. This spectrometer is designed to implement a program of precise measurement of pion β decay π{sup}+ → π{sup}0 + e{sup}+ + v{sub}e at the Paul Scherrer Institute (Switzerland). A spherical calorimeter, consisting of 240 crystals of pure Csl scintillator and embracing a solid angle of ～3π, is the main detector of the setup. In addition, the spectrometer is composed of an active collimator (which also acts as a beam degrader), a segmented active plastic target, two multiwire cylindrical proportional chambers, a 20-element cylindrical plastic hodoscope, and veto counters of cosmic muons.