1. Detectors for PREx Collaboration Meeting, April 17-18, 2009 Piotr Decowski, Smith College Krishna Kumar. UMass

2. January 2008 test Dustin’s analysis 1cm thick quartz 0.5cm thick quartz MPV = 25.48 GSigma = 5.65 Net width = 5.34 (21%) Net RMS = 8.57 (34%) (5.34) 2 = 28.5 MPV = 14.37 GSigma = 4.59 Net width = 4.20 (29%) Net RMS = 5.49 (38%) (4.20) 2 = 17.64 Pedestal width = 1.85 N PE = 1/(.21) 2 = 22.7N PE = 1/(.29) 2 = 11.9 Statistics:

3. January 2008 test Absolute determination of N PE : N PE * (1.602*10 -19 C)*PMTGain = MPV(ch)*(50*10 -15 C/ch) LeCroy 1881M ADC NEEDED!

4. Measurement of PMT gain Anna Boehle, Diana Jaunzeikare, Smith College 21 fC/ch

5. Measurement of PMT gain, cont PMT: Hamamatsu R7723Q (fused silica window) PMT # ZK40033: Gain @ -2000V = 4.384*10 5

6. Results Statistics: Absolute gain: N PE = 22.7 N PE = 11.9 N PE = 18.1N PE = 10.2 1cm thick quartz0.5cm thick quartz N PE (1cm)/N PE (0.5cm) = 1.90 N PE (1cm)/N PE (0.5cm) = 1.77 (exp) Note: without pedestal width subtraction statistics gives N PE (1cm) = 20.3, and N PE (1cm) = 9.8

7. GEANT4 Simulations Jon Wexler, UMass Quartz block PMT cathode Cone mirrorTube mirror

8. Simulations: photon energy range 185 nm Quartz cut 500 nm QE cut 380nm Alzak cut Standard PMT QE cut PMT QE: Alzak: reflectivity 93 - 98% Anodized Al reflectivity: 85 - 87%

9. Simulations: results 1cm thick quartz0.5cm thick quartz N PE = 22.7N PE = 11.9 N PE = 18.1N PE = 10.2 N PE = 26.6N PE = 13.9Sim: Stat: Gain: Simulations overestimate experimental results by ~ 30% (there is room for improvements!)

10. Simulations: Al vs Alzak 1cm thick quartz 0.5cm thick quartz Al Alzak N PE = 26.6N PE = 13.9 N PE = 64.5N PE = 34.0 Improvement: factor 2.4 !

11. HRS focal plane Bob Michaels

12. Detector concept 10 cm Quartz 0.5cm (0.25cm) thick Al mirror tube 2” PMT Optimize Expected ~20 PE per PMT/electron (~4nA @1GHz) Top view Two stacked 0.25cm thick detectors? LED

13. Detector configuration e - beam Det 1 Det 2 A_T Det

14. Conclusions and plan 1.Simulations are reproducing experimental data well. 2.We have tool to optimize geometry of new detectors with larger quartz accommodating larger footprint of the Pb elastic peak. 3.Use of anodized aluminum instead of Alzak and PMTs with fused silica window significantly increases number of PE’s. Plan for nearest future: 1.Construction of two prototypes of detectors with existing quartz blocks to test PE enhancement due to Al mirrors. These detectors will be used at the beginning of the HAPEX run. 2.Optimization of geometry of detectors with larger quartz blocks. 3.Construction of A_T detectors (similar to used in the January 2008 tests). 2.Construction of small plastic scintillator pads which will be mounted above the main detectors, and in counting mode will substitute S0 detector.