E. Schyns

The Barrel Ring Imaging Cherenkov counter of DELPHI

Abstract A short explanation is given of the Barrel Ring Imaging CHerenkov (BRICH) detector and its performance. We discuss in brief some of the requirements to run this detector. Special attention is paid to the functioning of the Cherenkov photon detector — a photosensitive gas-filled drift chamber where the photoelectrons drift to a MWPC of special construction. We illustrate the BRICH performance with some preliminary results.

Technology of photocathode production

Abstract Thin film photocathodes have been developed both for gas and vacuum based photodetectors. Over the last years we have gained experience in fabricating large area reflective CsI and semi-transparent mono- and bialkali-cathodes, i.e. Rb 2 Te and K 2 CsSb. Today we are producing stable cathodes with excellent quantum efficiency for large MWPC based pad detectors and Hybrid Photodiodes on a routine basis. We give an overview of the technologies involved in the preparation of the substrates, the cathode processing and the encapsulation. The dedicated processing plants and instrumentation, required for monitoring and characterisation, is discussed.

Identification of high p⊥ particles with the STAR-RICH detector

Abstract The STAR-RICH detector extends the particle identification capabilities of the STAR experiment for charged hadrons at mid-rapidity. This detector represents the first use of a proximity-focusing CsI-based RICH detector in a collider experiment. It provides identification of pions and kaons up to 3 GeV /c and protons up to 5 GeV /c . The characteristics and performance of the device in the inaugural RHIC run are described.

Status of large area CsI photocathode developments

The development of large area reflective CsI photocathodes for RICH detectors is reviewed in the context of their production process and their performance. The quantum efficiencies of six large photocathodes recently produced by ALICE are compared with results available from the large photocathodes at HADES and STAR and with earlier R&D results obtained on small area samples. The CsI coating parameters and new developments in the domain of the production and the preparation of substrates are discussed in relation with the photocathode performance.

The CSI-based RICH detector array for the identification of high momentum particles in ALICE

Abstract After ten years of R&D activities, an array of seven proximity focusing RICH modules is being built to identify π - K in the range 1 p c and K-p in the range 1.5 p 2 , represents the largest scale application of MWPCs with high Quantum Efficiency (QE) CsI segmented photo-cathodes for the Cherenkov photon conversion. An overview of the RICH layout, the technique of photocathode production, the front-end (FE) and readout (R/O) electronics and finally the detector control system (DCS), are presented.

Study of the quantum efficiency of CsI photo-cathodes exposed to oxygen and water vapour

The operation of CsI photocathodes in gaseous detectors requires special attention to the purity of the applied gas mixtures. We have studied the influence of oxygen and water vapour contaminations on the performance of CsI photocathodes for the ALICE HMPID RICH prototype. Measurements were done through comparison of Cherenkov rings obtained from beam tests. Increased levels of oxygen and water vapour did not show any effect on the performance. The results of this study found a direct application in the way of storing CsI photocathodes over long periods and in particular in the shipment of the HMPID prototype from CERN to the STAR experiment at BNL. # 2001 Elsevier Science B.V. All rights reserved.

Cleaning and recirculation of perfluorohexane (C6F14) in the STAR-RICH detector

Abstract A RICH detector with a CsI photo-cathode and liquid perfluorohexane radiator has been installed in the STAR experiment at RHIC. The liquid is continuously cleaned and distributed to a quartz containment vessel within the detector by a closed recirculation system. A VUV spectrometer is connected to the system which monitors the optical transparency of the liquid. This measurement provides one of the pieces of information necessary to model the number of Cherenkov photons which reach the pad plane. A description of the liquid recirculation system and the cleaning procedure for the liquid as well as the spectrometer is presented along with results of their performance.

Performance of the Forward RICH detector system at DELPHI

One quarter of the Forward Ring Imaging Cherenkov (Forward RICH) detector has been installed and operated in the DELPHI experiment. The detector covers the forward-backward regions (15 degrees >

Status of the HMPID CsI-RICH project for ALICE at the CERN/LHC

The ALICE (A Large Ion Collider Experiment) high momentum particle identification (HMPID) detector, presently under construction, consists of seven identical proximity focusing ring imaging Cherenkov (RICH) counters exploiting large area CsI photocathodes for Cherenkov light imaging. With a total area of 11 m/sup 2/, it represents the largest CsI-RICH system ever used in High Energy Physics. The detector layout, assembly and quality checks will be presented, with particular emphasis on CsI photocathodes mass production. A validation procedure has been established combining the results of the photocathode response mapping obtained in a dedicated VUV scanner with test beam data. The long-term stability has also been studied by irradiation with a Sr-90 source of a final size CsI photocathode inside a detector prototype.The ALICE (A Large Ion Collider Experiment) high momentum particle identification (HMPID) detector, presently under construction, consists of seven identical proximity focusing ring imaging Cherenkov (RICH) counters exploiting large area CsI photocathodes for Cherenkov light imaging. With a total area of 11 m/sup 2/, it represents the largest CsI-RICH system ever used in High Energy Physics. The detector layout, assembly and quality checks will be presented, with particular emphasis on CsI photocathodes mass production. A validation procedure has been established combining the results of the photocathode response mapping obtained in a dedicated VUV scanner with test beam data. The long-term stability has also been studied by irradiation with a Sr-90 source of a final size CsI photocathode inside a detector prototype.

Recent results from the DELPHI barrel ring imaging Cherenkov counter

The DELPHI detector installed in the LEP (Large Electron-Positron Collider) is equipped with RICH (ring imaging Cherenkov) counters. The barrel part incorporates a liquid (C/sub 6/F/sub 14/) and a gaseous (C/sub 5/F/sub 12/) radiator, providing particle identification up to 20 GeV/c. The Cherenkov photons of both radiators are detected by TPC (time projection chamber)-like photon detectors. The drift gas (75% CH/sub 4/+25% C/sub 2/H/sub 6/) is doped with TMAE (tetrakis-dimethylamine-ethylene) by which the ultraviolet Cherenkov photons are converted into single free photoelectrons. These are drifted towards multiwire proportional chambers 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 C/sub 2/F/sub 6/ 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 good functioning of the focussing mirrors. >