THIN SCINTILLATING TILES WITH HIGH LIGHT YIELD FOR THE OPAL ENDCAPS

Arrays of thin scintillating tiles with embedded wavelength shifting f ibre readout have been installed in the OPAL endcaps to improve trigge r performance, time resolution and hermeticity for experiments at LEP II. The arrays were required to have high single-particle detection ef ficiency, uniform response, low noise and good time resolution. Limite d space for the detector, and a strong magnetic field in the endcap re gion, resulted in a need for high light output per unit thickness of s cintillator, and remote readout. In addition, because of limited space for readout cables, a high light yield per embedded fibre was require d. This paper describes the design and construction of a tile array th at satisfies these requirements. A light yield of 14 photoelectrons pe r minimum ionizing particle and a time resolution of 3 ns were obtaine d during 1997 LEP operation. (C) 1998 Elsevier Science B.V. All rights reserved.