A study of the monitoring of radiation damage to CMS ECAL crystals, performed at X5-GIF

The ratio R, defined as the fractional decrease in the beam signal divided by the fractional decrease in the light monitoring signal, was measured at the GIF-X5 facility for a set of 20 ECAL barrel crystals. The dependence of R on the wavelength of the injected monitoring light and its path length in the crystals was studied. Measurements of the inter-crystal variation in R are presented for 10 pre-production crystals. Results on the dependence of signal loss on the irradiation profile are given. The use of lead filters, placed between a 137Cs source and a crystal, to reproduce different longitudinal irradiation profiles has been tested. (author)