Author/Authors :
Hazen، نويسنده , , E and Lawlor، نويسنده , , C and Rohlf، نويسنده , , Maran J.W and Wu، نويسنده , , S.X and Baumbaugh، نويسنده , , A and Elias، نويسنده , , J.E and Freeman، نويسنده , , J and Green، نويسنده , , D and Lazic، نويسنده , , D and Los، نويسنده , , S and Ronzhin، نويسنده , , A and Sergueev، نويسنده , , S and Shaw، نويسنده , , T and Vidal، نويسنده , , R and Whitmore، نويسنده , , J and Zimmerman، نويسنده , , T and Adams، نويسنده , , M and Burchesky، نويسنده , , K an، نويسنده ,
Abstract :
Relative calibration of the scintillator tiles used in the hadronic calorimeter for the Compact Muon Solenoid detector at the CERN Large Hadron Collider is established and maintained using a radioactive source technique. A movable source can be positioned remotely to illuminate each scintillator tile individually, and the resulting photo-detector current is measured to provide the relative calibration. The unique measurement technique described here makes use of the normal high-speed data acquisition system required for signal digitization at the 40 MHz collider frequency. The data paths for collider measurements and source measurements are then identical, and systematic uncertainties associated with having different signal paths are avoided. In this high-speed mode, the source signal is observed as a Poisson photo-electron distribution with a mean that is smaller than the width of the electronics noise (pedestal) distribution. We report demonstration of the technique using prototype electronics for the complete readout chain and show the typical response observed with a 144 channel test beam system. The electronics noise has a root-mean-square of 1.6 least counts, and a 1 mCi source produces a shift of the mean value of 0.1 least counts. Because of the speed of the data acquisition system, this shift can be measured to a statistical precision better than a fraction of a percent on a millisecond time scale. The result is reproducible to better than 2% over a time scale of 1 month.
