A new threshold Cherenkov detector has been
built for the detection of charged pions in the focal plane of a
magnetic spectrograph. Silica aerogel with refractive index of n
= 1:05 is applied as a radiator. The detector exhibits a very high
detection efficiency for pions with momenta ³900MeV/c.
Using two Cherenkov detectors in series a very high pion
suppression factor of 105 was achieved.