1. 1 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL - The PROBLEM - The IDEA - The SETUP - Some RESULTS

2. 2 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The PROBLEM  In order to discover a light Higgs decaying in gg  we need an excellent calorimeter, with a constant term of ~0.5%; so we must have:  CMS-ECAL PbWO 4 crystals are radiation hard (no damage to scintillation process) but there are small changes in transparency due to radiation exposure. The change is of the order of 2-3 % and is fairly rapid ( hours ).The change of transparency light will be monitored in situ with a laser and a correction to particles signal will be applied: R =  particle /  monitoring The crystal-to-crystal variation of R must be limited to about 5% to avoid R becoming another calibration constant. crystal-to-crystal inter-calibration error must be limited to ~0.4%;

3. 3 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The IDEA  The ideal solution would be to measure R for all the 71964 crystal of the CMS-ECAL, but this is practically impossible;  the solution is to do systematic measurements of R for group of crystals and correlate the results with other important parameters of the crystals. To do that, we built a setup at the General Irradiation Facility (GIF) of CERN. With it we can do (at the same time) : Irradiate with a Cs 137  source (E  =0.662 MeV, dose rate=15 rad/h i.e. LHC conditions) Excite the crystals with SPS e beam (50 and 100 GeV) Excite the crystals with UV laser ( =337  10 nm, 1.55mJ/pulse, t =600 ps) Monitor the transmission of the crystals at different wave length:   LED ( =450  50 nm, t=500 ns)   Xenon lamp ( =400, 420, 440, 500, 524 nm, t=1  s) Transmission UV Laser LED

4. 4 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP GIF is a multi-CERN-users facility, due to that three main constraints exist:  very little space available;  very few days of beam per year (8-10 days) ;  we cannot take at the same time data and irradiate with Caesium source;  we cannot take at the same time e data and irradiate with Caesium source;  UV laser can replace the beam;  UV laser can replace the e beam;  crystals are tested in batches of 5;  the setup can move from and back the irradiation position to the beam, and allows to scan the 5 crystals with the electrons

5. 5 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP  Cs137 irradiation is done transversally to the crystal  The light detectors for the crystals are standard CMS-ECAL APDs  It’s very important to monitor the different light sources: a 6th crystal and a PM are installed to monitor all light sources; a PIN diode is used to monitor the laser  The gain is monitored periodically with a constant charge injected to the amplifiers (Test Pulse)  The 5 different triggers(LED, Laser, Lamp, Beam, Test Pulse, Pedestals) are generated asynchronously

6. 6 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Irradiation procedure  24 hours of stabilisation: at the end of the stabilisation, the beam is tuned on crystal 5 (the lowest); just before the irradiation starts, three scans per crystals with electrons are done  Irradiation starts, it lasts ~48h (~700 rad) : during the first two hours of irradiation the scan in the beam is done every 30 minutes; then the scan is done every hour for the next 8 hours of irradiation; then the scan is done every 2 hours till the end of the irradiation;  Sometime a recovery is done, the scan is done every two hours.  Crystals are taken out and annealed in oven. P.S. one scan lasts ~14 minutes (~ 3 minutes per crystal). In total 7000 electrons per crystals are kept in data, (out of 250.000 electrons hitting the crystals). This corresponds to a dose of ~2 rad per crystal per scan.

7. 7 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP LED box Laser fiber Lamp fiber Cooling pipes Crystals box

8. 8 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP PM PIN diode for Laser

9. 9 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP Cooling Scintillators trigger block APDs block

10. 10 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP APD Temperature probe Beamdirection Lead radiation screen

11. 11 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP Irradiation window

12. 12 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP Beam direction Crystal Temperature probe Beam trigger scintillator Lamp fiber Laser fiber LED fiber

13. 13 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP

14. 14 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The SETUP Laser box

15. 15 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Some RESULTS  The results I will show are still preliminary  Results are from data taken this summer: SPS e beam of 50 and 100 GeV; 10 different production barrel crystal were irradiated, 5 of them 2 times and 5 of them 4 times.  Our goals of this summer were: confirm that UV laser can replace the beam; confirm that UV laser can replace the e beam; check the reproducibility of the results; check the reproducibility of the results; first evaluation of the crystal-to-crystal variation of R first evaluation of the crystal-to-crystal variation of R.

16. 16 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The BEAM Drift chamber x Drift chamber y 1 cm ADC cry1 ADC cry2 ADC cry3 ADC cry4 ADC cry5

17. 17 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Typical irradiation curve 330 rad

18. 18 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Temperature correction CoCoCoCo  S/S as a function of  T/T UV Laser: 2.5% per 0.1 Cº LED: 0.8% per C o

19. 19 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como R calculation  LED  LASER Distribution of  LASER /  LED (i.e. R) 1dim gaussian fit 2dim linear fit Distribution of S LASER versus S LED  BEAM S LED S LASER S BEAM

20. 20 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como The best: Stabilisation Irradiation Recovery Exponential fit: Irradiation decay time is 5 times faster than Recovery rime (R is calculated doing the ratio of the Exponential functions. No problems from normalisation !)

21. 21 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Reproducibility The same crystal (9257) has been irradiated several times. The variance of R is 5%

22. 22 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como R dependence from R dependence from

23. 23 P.Rebecchi (CERN) “Monitoring of radiation damage of PbWO 4 crystals under strong Cs 137  irradiation in GIF-ECAL” “Advanced Technology and Particle Physics” conference, 18 October 2001 Como Conclusions  GIF-ECAL is a setup which allows to monitor the change in transparency of PbWO 4 CMS-ECAL crystals due to radiation exposure (LHC dose rate);  this summer test-beam showed that: UV Laser can reproduce the e beam crystal excitation (R~1.2) good reproducibility of results (~5%) the analysis is not yet fine enough in order to reduce measurement error such that the crystal-to-crystal dispersion can be extracted A measurement error less than 5% is needed (actually around 15%) improve the analysis improve the setup SYSTEMATIC irradiations