HKS Aerogel Cerenkov counter

The expected particle rates have been given in section 3.6 and table 10. From this it has been concluded that pions in the HKS should be suppressed by a factor of roughly $10^{-4}$ on the trigger level. Silica aerogel Cerenkov counters have been operated successfully in similar momentum ranges with detection efficiencies of 98 to 99%. Therefore, at least two detectors will be necessary to achieve 99.99% efficiency for pion detection which will allow to suppress them by $10^{-4}$. In order to keep the individual PMT rates low and also allow for more sophisticated trigger schemes that distinguish between multiple tracks, the detector should be segmented across the focal plane of the spectrometer. At the location of the detector the simulated envelope for good tracks is roughly $\pm10$ cm in $y$-directions and 125 cm in bending direction, $x$. To allow for some slop, the active area of the detector should be roughly $140\times 40$ cm$^2$.