A Total Reflection Type Cerenkov Counter with High Efficiency

A threshold-type Cerenkov counter which makes use of total reflection in a Lucite radiator, is constructed and tested using pion beams with various velocities. The detection efficiency of about 100% for relativistic particles (β≈1) is obtained. The detection threshold is found to be β≈0.9, whose value is expected from the calculation assuming the index of refraction of Lucite to be 1.49. The counter is successfully used to separate K± mesons from pions in the momentum range below 700 MeV.