Large aperture gas Cherenkov counters with good rejection of slow particles

Observation of Interference between Ĉerenkov and Synchrotron Radiation

“…We again attribute this primarily to transition radiation, which is calculated below to be a factor of 10 stronger than synchrotron radiation in the rather weak magnetic field. We estimate that scintillation of the helium gas, 15 which varies linearly with pressure, was about T as large as transition radiation just below the Cerenkov threshold.…”

“…The upstream end of the radiator volume was defined by a baffle, also oriented at 45° to the beam. The interior of the detector was painted black to suppress the collection of light from scintillation of the helium gas 15 or from Cerenkov radiation in the quartz coating of the mirror.…”

Measurement of electron beam polarization at the SLC

“…The threshold can of course be varied by changing the pressure or the type of gas. It has been shown by Heintze, et al 4 and verified by us that ,8-butylene has one of the lowest scintillating efficiencies of any gas in the wavelength region to which our phototubes are sensitive. The fact that Cherenkov light is strongly collimated whereas scintillation light is isotropic provides us with another powerful means of rejecting background.…”

“…Rapid and essentially 4 bias-free reversals of photon and/or electron polarization will minimize most systematic effects. The scattered electrons are contained in a cone of half-angle less than 10 microradians with respect to the beam axis.…”

A monitor for gamma radiation at zero degrees from the SLC collision point

“…In order to minimize this, the counter is filled with ethylene [7]. If nitrogen were >-_T_ to be used, the resulting background would be equivalent-to the beamstrahlung -+-.-at a luminosity of 102gcm-2seci l. Since electron thresholds in the range of 20 _-MeV are needed, it follows that the counter must be operated at pressures below atmospheric.…”