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

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

Workshop calorimetry October 31, x12 = 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

Workshop calorimetry October 31, Experimental setup

Workshop calorimetry October 31, 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

Workshop calorimetry October 31, 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

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

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

Workshop calorimetry October 31, 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

Workshop calorimetry October 31, 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

Workshop calorimetry October 31, 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

Workshop calorimetry October 31, Radiation hardness Lead fluoride –E E kRad Attenuation –3 calibration points and interpolation Curing tests done with beam at Pocatello

Workshop calorimetry October 31, Radiation damage Lead fluoride –E / E kRad Attenuation

Workshop calorimetry October 31, Curing

Workshop calorimetry October 31, 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