J. Dolbeau

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.

Current achievements of the DELPHI ring imaging Cherenkov detector

Abstract The DELPHI experiment has already collected 2.5 million Z 0 decays with the ring imaging Cherenkov detector (RICH) operational. This detector, covering most of the solid angle, is designed to perform π K separation from 0.8 to 20 GeV/ c and K/p separation from 0.8 to 35 GeV/ c . After a brief detector description we discuss the actual operating conditions, the data monitoring and the signal treatment. The collected data from Z 0 decays and the detector response to signals from the calibration system are used to evaluate the performance of the RICH system.

Observation of a fully reconstructed D0D0 pair with long proper lifetimes in a high resolution hydrogen bubble chamber and the European hybrid spectrometer

Abstract In an experiment with 360 GeV/ c π − beam at the CERN SPS using the high resolution hydrogen bubble chamber LEBC and the European Hybrid Spectrometer, an event has been observed of the type π − p → D 0 D 0 + 8 prongs. The fully reconstructed decay modes are D 0 → K − π + π 0 π 0 and D 0 → K + π + π − π − , with all six charged tracks being detected in the spectrometer and all four photons from the π 0 decays detected in the lead glass gamma detection system. The D 0 has momentum 119.0 ± 0.6 GeV/ c , x F = 0.31, length 4.1 ± 0.1 mm and proper lifetime (2.1 ± 0.1) × 10 −13 s. The D 0 has momentum 78.5 ± 0.3 GeV/ c , x F = 0.19, length 7.5 ± 0.1 mm and proper lifetime (5.9 ± 0.1) × 10 −13 s.

The photo-detector for the EUSO experiment

Abstract The EUSO experiment is currently under study by ESA for a possible installation on the International Space Station. The experiment is designed to study, by means of a space-based observational apparatus, the Extensive Air Showers produced in the atmosphere by Extreme High-Energy Cosmic Rays. The design of a fast, single-photon sensitive photo-detector in the near UV, covering a large area with a few hundreds thousands pixels, and suitable for 3 years of operation in space is a challenging task. The basic aspects of the current EUSO photo-detector design, based on the presently known requirements and constraints, and the results of the preliminary studies carried on so far will be described.

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. >

The ring imaging Cherenkov detectors of DELPHI

A ring imaging Cherenkov (RICH) detector system has been built and is now in full operation within the DELPHI experiment. Large data samples of Z/sup 0/ decays are being collected with good resolution on the observed Cherenkov angles. Several studies of Z/sup 0/ decays using the RICH have already been performed on limited samples. Disturbance of the detector operation caused by shrinkage of polymeric construction materials and by migration of radiator substance is reported. These effects have been counteracted and do not endanger the quality of the data. >

Performance of the ring imaging Cherenkov detector of DELPHI

Abstract The general purpose particle detector DELPHI at the Large Electron Positron collider at CERN was built to give the complete information of each event. DELPHI uses ring imaging Cherenkov counters to provide hadron identification in most of the momentum range below 45 GeV/ c and over almost the full solid angle. Charged particles traversing gaseous and liquid fluorocarbon radiators create photons used for Cherenkov angle reconstruction. Some of the design features of the detector will be presented, with emphasis on the experience which was gained in the operation of these large systems. The hadron identification power of the ring imaging Cherenkov detector closely meets the main design values. Data processing and performance of the detector will be discussed using dimuon events collected during 1994. Pion rejection factors for kaon tagging will be shown.

Performance of the Barrel Ring Imaging Cherenkov counter of DELPHI

The Barrel Ring Imaging Cherenkov detector of the DELPHI experiment at LEP provides particle identification by the detection of the radiation emitted in UV transparent perfluorocarbons. We will present the principles of the operation of the detector together with a discussion of the automatized control of all the relevant physical parameters. The observed performances of the detector are very close to their design values. >

Estimation of the lifetime of short-lived particles using their production characteristics

Estimators with minimal systematic and statistical errors are developed for the determination of the lifetimes of short-lived particles whose individual momenta are unknown. These estimators make use of the measured decay lengths and the a priori known production characteristics. The detection of the short-lived particles through the impact parameter of their charged decay products leads to additional complications which are taken into account. The biases and statistical errors inherent in using simpler approximate lifetime estimators are also discussed. Illustrative results are given for the lifetime of the D0 mesons using the data sample from CERN experiment NA27.