Résumé du preprint DAPNIA-01-12

Simulation of light collection in the CMS lead tungstate crystals with the program Litrani: coating and surface effects
R. Chipaux, F.-X Gentit
The  accuracy  of  the  lead  tungstate  electromagnetic  calorimeter  of  the  CMS  experiment  under
construction at CERN relies, among other things, on the correction of the calibration parameter from
variations dues to crystal ageing. This ageing will be measured by a so-called monitoring system, but
the  relation  between monitoring  and  calibration  parameter  variations  is  not  so  trivial,  and  depends
much on the overall optical characteristics of crystal and photodetector. We present here simulations
done  with  the program  Litrani  based on  real  ageing  data  for  a  realistic CMS  crystal  with  a  defined
surface  quality  (optically  polished, with  or  without one  lateral  face  slightly  depolished),  covered by
coatings of various characteristics, from totally absorbing to nominal aluminum or diffusing medium.
The  correlation  coefficient  between  monitoring  and  scintillation  signals  depends  greatly  on  these
characteristics, and varies between about 1.3 and more than 10 (the optimum being one).


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