1. Lead Fluoride Calorimeter for Deeply Virtual Compton Scattering in Hall A Alexandre Camsonne Hall A Jefferson Laboratory October 31 st 2008

2. Outline Design and characteristics of lead fluoride Triggering and electronics Background effects Radiation damage Conclusion

3. Workshop calorimetry October 31, 2008 3 11x12 = 132 blocks 3cmx3cmx18.6cm 110 cm from the target 1msr per block PMT R7700 (8 stages version of R5900 ) Hamamatsu 8 stages Gain : 10 4 Rise time 2 ns FWHM 6 ns Lead fluoride density 7.77 g.cm 3 X 0 =0.93 cm length=20X 0 Molière radius = 2.2 cm Pure Cerenkov : not sensitive to charged hadronic background Good radiation hardness Electromagnetic calorimeter 1 Photoelectron per MeV, Energy resolution 4.2GeV : 2.4 % Position resolution: 2 mm

4. Workshop calorimetry October 31, 2008 4 Experimental setup

5. Workshop calorimetry October 31, 2008 5 Background reduction Scattering chamber 1 cm Al as shielding 15 cm 5 cm beam dump Liquid H 2 target 110 cm High luminosity running possible by reducing secondary background source PbF 2

6. Workshop calorimetry October 31, 2008 6 Dedicated electronics Sampling system –1GHz Analog Memory sampling system –Store information in analog form to reduce dead time from encoding to leave time for generation of photon trigger –Resolve pile-up event offline Calorimeter trigger –Rate reduction with coincidence trigger –FADC based –Digital summing –Data reduction

7. Workshop calorimetry October 31, 2008 7 Dedicated electronics Sampling system –1GHz Analog Memory sampling system

8. Workshop calorimetry October 31, 2008 8 Typical calorimeter pulse Singles rate in one block up to 1 MHz

9. Workshop calorimetry October 31, 2008 9 Dedicated electronics Sampling system –1GHz Analog Memory sampling system –Store information in analog form to reduce dead time from encoding to leave time for generation of photon trigger –Resolve pile-up event offline Calorimeter trigger –Rate reduction with coincidence trigger –FADC based –Digital summing –Data reduction

10. Workshop calorimetry October 31, 2008 10 Coincidence photon electron trigger generated in 440 ns 132 calorimeter channels Selected data By computer Field Programmable Gate Array Spectrometer trigger FPGA Readout pattern FPGA Calorimeter trigger Fast clear of ARS Tower acquisition

11. Workshop calorimetry October 31, 2008 11 Low energy background Very low energy background piles up as a DC current Monitoring of PMT anode current limited to less than 20 uA AC coupled electronics Lower gain PMT and active base

12. Workshop calorimetry October 31, 2008 12 Radiation hardness Lead fluoride –E00-110 E03-106 750 kRad Attenuation –3 calibration points and interpolation Curing tests done with beam at Pocatello

13. Workshop calorimetry October 31, 2008 13 Radiation damage Lead fluoride –E00-110 / E03-106 750 kRad Attenuation

14. Workshop calorimetry October 31, 2008 14 Curing

15. Workshop calorimetry October 31, 2008 15 Conclusion Lead fluoride was successfully used for Hall A DVCS Use of digital summing trigger to generate coincidence electron photon trigger Flash ADC type readout to deal with high energy pile Use of active base and lower gain PMTs to reduce effect of low energy background Radiation hardness Curing method being investigated Will be used for 6 and 12 GeV Hall A experiment