Crystal conditioning for high-energy physics detectors

In homogeneous high-resolution calorimetry for particle physics, scintillating crystals can now be considered as a mature technique. In the past decades, several large high-energy experiments have included crystal calorimeters from which a considerable harvest of physics results could be made. To extract the ultimate precision from such calorimeters, great care must be taken in the crystal conditioning, i.e. machining and wrapping or coating. These operations have a strong influence on some key crystal properties for the calorimeter energy resolution, such as light yield and light collection uniformity. In this note, some aspects of machining and of the techniques for uniformizing light collection will be discussed in the light of a recent experiment: L3 at LEP collider, using bismuth germanate crystals and an experiment in construction: CMS for LHC collider, using lead tungstate. To illustrate these techniques, results obtained on medium-scale crystal productions will be shown

Status of PWO crystal production for the electromagnetic calorimeter of CMS and of its construction

The CMS Electromagnetic Calorimeter will be composed of nearly 80,000 lead tungstate crystals. Owing to the high-energy resolution aimed at it and to the hostile Large Hadron Collider (LHC) radiation environment, a rigorous quality control of the crystals is performed on several parameters such as light yield, uniformity of the light collection or radiation hardness. The results of this quality control for the first 15,000 crystals delivered and characterized at the CERN Regional Centre by Bogoroditsk Techno-Chemical Plant are presented here. In addition, an overview of the construction status is given

Status of PbWO4PbWO_{4} crystals R&D and preproduction from BTCP for the CMS calorimeter

The electromagnetic calorimeter of the CMS experiment is now entering the construction phase. Consequently the crystal production will soon start. The preproduction phase which started in August 1998, is foreseen to allow for further optimisation of the final crystal production scheme. A general overview about the quality and characteristics of the first large batch of the preproduction crystals will be given and the results will be discussed with respect to the final production requirements needed for high resolution calorimetry for CMS. (11 refs)

Initial Tests on First Full-size Endcap Crystals

At the end of last year the first full size ECAL endcap crystals were delivered to CERN.Thirty in number, they were produced to the final geometrical specifications; 220mm long with a rear square face of 30mm and a front square face of 28.6mm. All were de livered polished. The visual inspection, dimension, transmission, light yield and light yield uniformity tests carried out since are discussed, with particular emphasis on the light yield uniformity. The results are very encouraging

Cross-Calibration of Two Automatic Quality Control Systems for the CMS ECAL Crystals

The barrel part of the CMS electromagnetic calorimeter consists of about 60000 PWO crystals and will be assembled in two Regional Centers, nearby Rome and at CERN. Two automatic machines have been designed to check the crystal quality before assembly. The main crystal characteristics are compared to a set of specifications included in the contract with the crystal producers. The stability and intercalibration between the two is a fundamental issue, which has to be controlled during the whole construction phase. This paper describes the checks that were made in order to cross calibrate the measurements and to guarantee a proper selection of crystals for the detector