H. Kawahara

THE DIRC COUNTER: A NEW TYPE OF PARTICLE IDENTIFICATION DEVICE FOR B FACTORIES*

A very thin, solid radiator, totally internally reflecting, imaging Cherenkov counter (DIRC) is described. This device is well matched to requirements at an asymmetric e+e- B Factory. the hadronic charged particle identification 1. INTR~IXJ~TI~N Particle identification at a B factory is difficult, and highly constrained by the machine environment and the need for good energy measurement of soft photons in the calorimeter which surrounds the particle identification device [l]. Because of the high beam crossing rate and the potential for large backgrounds, the particle identification detector must be robust and relatively fast. Good r~‘dK separation is required over a wide momentum range between about 0.25 and 4 GeV/c. Most detectors measure dE/dx in the tracking chamber which allows good X/K separation up to about 600 MeV/c, but a specific identification device is required over most of the momentum region [2]. The amount of material in the device should be small (preferably less than 10% LRAD) and should be distributed as close as possible to the calorimeter in order to avoid degradation in the resolution performance of the calorimeter, and the loss of low energy conversion electrons in the magnetic field. In addition, the cost of the high quality calorimeter scales roughly like the radius squared and there will be substantial cost savings if the particle identification device can be made thin.

TEST OF A LARGE SCALE PROTOTYPE OF THE DIRC, A CHERENKOV IMAGING DETECTOR BASED ON TOTAL INTERNAL REFLECTION FOR BABAR AT PEP-II

Abstract The principles of the DiRC ring imaging Cherenkov technique are briefly explained and its choice for the B a B ar detector particle identification system is motivated. A large scale prototype of the DIRC for the B a B ar experiment is then described. Details of the design of this prototype and its test in a hadronic particle beam at the CERN-PS are presented, and results from various prototype and test configurations are given. For example, after correcting for geometrical acceptance and estimated collection effects, the number of photoelectrons was measured to be 146 ± 1.8 ± 9 cm −1 , for a track angle of 20° at zero photon transmission distance. The effective attenuation loss was measured to be 4.1 ± 0.7% per meter of bar length, and the observed single photon resolution was 10.0 ± 0.2 mrad. This performance is consistent with what was expected from earlier tests and Monte Carlo simulations, and will be fully adequate for the physics demands of the B a B ar experiment.

Performance of the CRID at SLD

Abstract This paper describes the performance of a large 4π Cherenkov Ring Imaging Detector (CRID) in the SLD experiment at the SLC at SLAC. We compare the most recent SLD results with those obtained during the R&D period, discuss various design features, and highlight some specific lessons derived from three years of operation.

DIRC, the internally reflecting ring imaging Cherenkov detector for BABAR

The DIRC is a new type of Cherenkov imaging device that will be used for the first time in the BABAR detector at the asymmetric B-factory, PEP-II. It is based on total internal reflection and uses long, rectangular bars made from synthetic fused silica as Cherenkov radiator and light guide. The principles of the DIRC ring imaging Cherenkov technique are explained and results from the prototype program are presented. Its choice for the BABAR detector particle identification system is motivated, followed by a discussion of the quartz radiator properties and the detector design.

An internally reflecting Cherenkov detector (DIRC): properties of the fused silica radiators

The DIRC, a new type of ring-imaging Cherenkov detector that images internally reflected Cherenkov light, is being constructed as the main hadronic particle identification component of the BABAR detector at SLAC. The device makes use of 5 meter long fused silica (colloquially called quartz) bars, which serve both as the Cherenkov radiators and as light pipes for transmitting the light to an array of photo-multiplier tubes. This paper describes a program of research and development aimed at determining whether bars that meet the stringent requirements of the DIRC can be obtained from commercial sources. The results of studies of bulk absorption of fused silica, surface finish, radiation damage and bulk inhomogeneities are discussed.

Production of 400 mirrors with high VUV reflectivity for use in the SLD Cherenkov ring imaging detector

Abstract The Stanford Large Detector for experimental particle physics detection at the SLAC Linear Collider contains a Cherenkov ring imaging detector (CRID). The barrel CRID mirrors have been successfully produced and installed. The industrial mirror production process, the quality control of the mirrors produced, and the results of the vacuum ultraviolet (VUV) reflectivity and mirror-shape accuracy are described. An average reflectivity of at least 80% for light at 160 nm and 85% for light in the 180–230 nm wavelength range has been achieved in the production of over 400 mirrors of a typical size of 30 by 30 cm. The surface roughness and optical distortion measurements imply that the light loss due to scattering is a few percent of the incident light and the angular error due to shape distortion is less than 1 mrad.

Monitor and control systems for the SLD Cherenkov ring-imaging detector

To help ensure the stable long-term operation of a Cherenkov Ring Imaging Detector at high efficiency, a comprehensive monitor and control system is being developed. This system will continuously monitor and maintain the correct operating temperatures, and will provide an on-line monitor of the pressures, flows, mixing, and purity of the various fluids. In addition the velocities and trajectories of Cherenkov photoelectrons drifting within the imaging chambers will be measured using a pulsed UV lamp and a fiberoptic light injection system.

The fluid systems for the SLD Cherenkov Ring Imaging Detector

The design and operation of the fluid delivery, monitor, and control systems for the SLD barrel Cherenkov Ring Imaging Detector (CRID) are described. The systems deliver drift gas (C/sub 2/H/sub 6/+TMAE), radiator gas (C/sub 5/F/sub 12/+N/sub 2/), and radiator liquid (C/sub 6/F/sub 14/). Measured critical quantities such as electron lifetime in the drift gas and ultraviolet (UV) transparencies of the radiator fluids, together with the operational experience, are reported. >

Obtaining physics results from the SLD CRID

Abstract We describe the likelihood ratio method used for particle identification in the SLD CRID, which allows the use of the entire momentum range covered by the liquid and gas radiators, including the threshold regions. Its application to two preliminary physics analyses is also described.

Construction and testing of the SLD Cerenkov Ring Imaging Detector

The construction of the Cherenkov Ring Imaging Detector (CRID) for the SLD (Stanford Linear Collider Large Detector) experiment at the SLAC (Stanford Linear Accelerator Center) Linear Collider and the testing of its components is reported. Results are included from testing the drift boxes, liquid radiator trays, and mirrors for the barrel CRID. The development of the support systems essential for the operation of the CRID, namely, gas and liquid recirculation systems and monitoring, are discussed. >