Specifications for Lead Tungstate Crystals Preproduction

After 3 years of extensive R&D the Bogoroditsk Techno-Chemical Plant in Russia is ready to enter a preproduction phase where 6000 Lead Tungstate crystals will be produced for the CMS electromagnetic calorimeter during a period of about 18 months. Although this is a demonstration test for the mass production, these crystals will have to be installed in the calorimeter and have therefore to comply with the very severe constraints imposed by the ambitious performance goal of the calorimeter in the high radiation environment of LHC. This paper describes and justifies the specifications for these preproduction crystals

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

Development of a Uniformisation Procedure for the PbW04 Crystals of the CMS Electromagnetic Calorimeter

The CMS electromagnetic calorimeter will consist of nearly 80,000 lead tungstate crystals, with 18 different geometries. The contribution of any non-uniformity in the light collection to the constant term in the energy resolution must be limited to 0.3%. A procedure capable of achieving this for the full calorimeter has been developed in the CERN EP-CMA group. A description of this method and the results obtained with the first few hundred pre-production crystals from Bogoroditsk, Russia are given in this note

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

Studies and Proposals for an Automatic Crystal Control System

This document presents the status of the studies for an Automatic Crystal Control System ( ACCOS) performed since autumn 1995 for the CMS collaboration. Evaluation of a startstop method for light yield, light uniformity and decay time measurements of PbWO4 crystals is presented, as well as the first results obtained with a compact double-beam spectrophotometer for transverse transmission. Various overall schemes are proposed for an integrated set-up including crystal dimension measurement. The initial financial evaluationperformed is also given