1. PREx detectors Progress report Krishna Kumar Keith Otis UMass Piotr Decowski Selamnesh Nida Smith College Collaboration Meeting, May 17-18,2007

2. HRS focal plane Keith Otis, UMass

3. Requirements: 1.Integrating 2.Radiation hard (~1 GHz) 3.Good resolution (<25%) 4.Small size Thin detector:

4. Challenges: PM output signal per one electron passing the detector: Relative error: SimulationsBinominal distribution Relative statistical error of the parity violating asymmetry: To minimize we have to maximize and For we need

5. However: For ( ) and expected rate of electrons ~1 GHz, the current at the PM output will be: We need a very low gain, linear tube!

6. Thin Quartz Detector Concept: quartz conical mirror tube mirror PM 15 cm 4 cm*4cm 2&32&3 Optimization: -- cone length (mirror angle) -- quartz thickness -- quartz position in the cone -- PM diameter (2 and 3) Electron energy 850 MeV

7. Cone length (5 mm quartz) Number of photons reaching PM Relative width of distributions 6 cm 39.162 2 inch PM d=2mm d=5mm d=10mm d=2mm 50 7 cm.14 Optimal choice: 2 inch PM, 6 cm cone, d = 2 mm 3 inch PM Cone length (cm)

8. Quartz thickness Average number of photons at PM Relative width of distribution Quartz thickness (mm) 2 inch PM peak width rms of full distribution 3 inch PM 5 mm onset of showering 4 mm 15 mm Optimal choice: 5 mm quartz block

9. Optimal detector parameters: Trapezoidal quartz block 0.5cm thick, 4cm*4cm upper surface Cone mirror 6 cm long, with quartz block positioned at the smaller opening of the cone 2 inch diameter PM Simulated performance: N Ph ~ 40, N Ph ~ 17% The design is robust - the resolution does not depend strongly on design parameters as well as condition of quartz surface (as a matter of fact, more rough surface improves resolution by ~1%)

10. Design concept Cone mirror to PM Tube mirror

11. Realization Cone Quartz holder Quartz Front tube

12. Plans Drawings of the detector parts are in an advanced stage Two prototypes will be built during this summer First beam tests planned for fall 2007 (in the Moller target area) Thin detector: Important issue: choice of proper photon detector for high intensity runs Stack detector: 4 - 5 quartz blocks 0.5cm - 1cm thick separated by tungsten radiator Simulations of optimal design (in progress)