The Firs Cerenkov Counters*

The separation of charged kaons from the more copiously produced pions adds significantly to the analyzing power of e+edetectors. Time-of-flight techniques provide this separation up to about 1 GeV/c. However, at PEP and PETRA energies a large proportion of particles have momenta above this range. A useful device to tag kaons above 1 GeVjc would be a threshold Cerenkov counter. Due to the tight bunching of particles in jets, the counter must have high segmentation. Unfortunately the need to keep phototubes of a conventional counter outside a magnetic field makes a light guide system difficult if not impossible to design. For this reason Cerenkov counters which use proportional chambers to detect the ultraviolet art (1150-1350 8) P of the spectrum h ave been developed. -3 The proportional chambers are doped with a small amount of benzene. Benzene is chosen because it has a high photoionization probability in this wavelength range.