A. Buys

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.

Results on heavy quark selection through an impact parameter trigger

The implementation of a trigger aimed at selecting those nuclear interactions which contain a charm particle is described. The trigger uses a fast emulator of the PDP-11 which calculates the impact parameter of the decaying charged tracks originating from the charm decay. An enrichment factor of 15 is thereby obtained. The results obtained show that, in its present implementation, this trigger, while giving a good enrichment factor, performs a correct rejection, since it does not eliminate many good events that would have been retained by the more sophisticated selection of the offline programs. >

Alignment and Cherenkov angle resolution of the DELPHI RICH

The particle separation power of a RICH depends crucially on the obtained resolution in Cherenkov angle. In order to obtain the highest possible resolution, a precise knowledge of the positions of detector elements, the refractive indices and the photon detection points is required. The photon detectors are equipped with calibration systems for the determination of drift velocities and Lorentz angles. An off-line alignment of the detector elements is performed to improve the Cherenkov angle resolution. Events of the type Z) → μ+ μ− are used, and special care is taken to minimize the influence of the background content on the Cherenkov angle data. Results from the 1994 physics run are presented. The obtained single photon resolution is compared with simulations. While the gas radiator resolution is in very good agreement, some additional smearing of the simulated photon positions is needed to reproduce the liquid data.

RICH IN OPERATING EXPERIMENTS

Abstract An overview of the performance of RICH detectors and the experience obtained with them is given, considering currently operating experiments and completed ones. The latest results and, more generally, the information that is not present in the Bari Workshop Proceedings, are emphasized.

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. >

Results on charm physics from WA82

Abstract Experiment WA82 studies the hadroproduction of charmed mesons with a 340 GeV/c pion beam and a 370 GeV/c proton beam. The high and clean statistics of collected charms has been used to measure the differential cross section and its dependence on target nucleon number. The analysis of semileptonic decay D→K ∗ eν is presented.

Monitoring of the ageing of the DELPHI Barrel RICH MWPCs

Abstract We describe a method to monitor ageing effects in the multiwire proportional chambers (MWPCs) of the barrel ring imaging Cherenkov (BRICH) detector of DELPHI. It is based on a measurement of plateau-curve characteristics and the shift of these as a function of the total collected charge. Results indicate that, as yet, no ageing effects are present.