RECENT RESULTS FROM THE DELPHI BARREL RING IMAGING CHERENKOV COUNTER

The DELPHI detector, installed at LEP, is equipped with RICH (Ring Imaging CHerenkov) counters. The Barrel part incorporates a liquid (C6F14) and a gaseous (C5F12) radiator providing particle identification up to 20GeV/c. The Cherenkov photons of both radiators are detected by TPC-like photon detectors. The drift gas (75% CH4 + 25% C2H6) is doped with TMAE, by which the UV Cherenkov photons are converted into single free photo-electrons. These are drifted towards MWPC's at the end of the drift tubes and the space coordinates of the conversion point are determined. One half of the Barrel RICH is now equipped with drift tubes and has provided results from the liquid radiator since spring 1990. The gas radiator has been tested with C2F6 as a preliminary filling since August 1990. The data obtained demonstrate the good particle identification potential. For the liquid radiator the number of detected photons per ring in hadron jets is N = 8, whereas for muon pairs (single tracks) N = 10 has been obtained. For the gas radiator 2.1 photons per track were observed, which demonstrates the good functioning of the focussing mirrors, as for C2F6 this is close to the expected value.