Ultraviolet Photon Detection in TMAE Using a Multistep Proportional Chamber

Cherenkov Ring Imaging using position-sensitive gas detectors is a new and very promising technique for charged particle identification In a wide range of momenta, allowing large geometrical acceptance and multitrack capability [1,2]. Several methods for detection and localization of ultra-violet photons over large surfaces have been devised [3-6]. One of them, based on the Multistep Proportional Chamber (MSPC) [7], has been already used operationally in a high rate experiment [8,9]. With triethylamine (TEA) as photoionizing vapour a good time resolution of around 50 ns could be achieved. However, the localization method used, a measurement of center-of-gravity of the induced charges on cathodes of a Multiwire Proportional Chamber, limits the number of simultaneous photon points in a ring than can be unambiguously reconstructed to around five or six, the two-photon resolution being 8-10 mm. This is not a drawback at very high momenta, where the necessity of using a radiating medium with index of refraction very close to unity results in a small number of photons; it seriously limits however the range of application of the method at lower momenta.