The hadron blind detector (HBD) in the PHENIX experiment at RHIC

Full text: A novel Hadron Blind Detector (HBD) is currently under installation as part of the PHENIX upgrade at RHIC and is expected to be operational in the forthcoming run in the fall of 2006. The primary goal of the HBD is to measure electron-positron pairs, particularly in the low mass region (< l GeV/c2), in the high multiplicity hadron environment in Au-Au collisions. By identifying and thereby rejecting the low momentum electron-positron pairs arising from the -0 decays and conversions, the detector would reduce the combinatorial background by about two orders of magnitude hitherto unachievable with the present set of detectors in PHENIX. The HBD is basically a Cherenkov detector operated with pure CF4 in a windowless configuration. CF4 acts as both the radiator and the detector gas. The active element of the detector consists of triple GEM (Gas Electron Multiplier) modules having a layer of CsI evaporated on the top face of the first GEM foil and serving as the photocathode. The 3-GEM combination, under optimized conditions gives a net gain of 104 producing large signals on the pad plane. Positioned close to collision vertex, the main body of the HBD consists of two identical arms covering 135 deg in azimuth and ±0.42 units in -. The geometrical layout, basic principle of operation, final design and construction techniques along with the expected performance of the HBD will be discussed. (author)