1. PREX main detector Piotr Decowski Aimee Shore Smith College Piotr Decowski Aimee Shore Smith College Kumar Krishna Jon Wexler Patrick Rogan Vireak Yim UMass Kumar Krishna Jon Wexler Patrick Rogan Vireak Yim UMass PREx Collaboration Meeting Feb. 19-20, 2010 PREx Collaboration Meeting Feb. 19-20, 2010

2. Outline Detector assembly in HRS focal plane Detector head and its optimization A T - hole detector Progress of construction Other tasks Issues

3. Detector assembly Beam Two pairs of GEMs Two main detectors Scintillator trigger Quartz blocks and reflectors

4. Detector assembly, cont. All dimensions and positioning in respect to the VDC are determined and fixed. The information about exact detector position will allow to finalize details of beam optics in the HRS hut (John LeRose)

5. Detector assembly mounted in the HRS focal plane Trigger Main detectors Beam X-Y movers Unistrut support GEMs

6. Another view

7. GEM support details GEMs ElectronicsSupports for electronics These parts will be machined in the Umass, UVA, and Smith College shops. Smith Colleges shop is equipped with computer controlled powerful water jet cutter, which wil be used to cut more elaborated shapes.

8. Location of the main detector head in the HRS focal plane (Dustins simulations) Quartz holder bar at save distance from the beam (no beam splash) Detector head PMT 14 cm long and 3.5 cm wide quartz

9. Detector head: Optimization of reflector 14 cm long quartz Conical mirror PMT Tube GEANT simulations: - range of reflectivity coefficients - specular versus diffuse reflection Geometry

10. Results of Simulations X dependence of PE number (dispersive direction) Y dependence of PE number (transverse direction) Specular reflection Diffuse reflection These regions were tested using cosmic rays PMT side PMT side 14 cm * 4 cm quartz For typical reflectivity 80 - 90 % expected number of PEs ~ 50 - 60

11. Setup for cosmic tests Quartz made from 6 smaller pieces PMT Lead filter One of the trigger detectors

12. Results from cosmic tests Region 1 Region 2 Number of PEs sqrt(PE) Painted flat mirrors Painted cone White paper cone Flat Al mirrors Painted quartz Al cone Wrapped mylar No mirrors Al cone No mirrors Flat Al mirrors Painted cone White paper cone Wrapped mylar Painted quartz Painted flat mirrors Best results Region 2 Best: Painted flat mirror? Painted quartz?

13. Paint 250 nm2500 nm 40 100

14. A T - hole detector Separate detector on X - Y movers attached to the 45 deg side yellow beam of the focal plane cage. 4 cm * 4 cm quartz tangent to the Cherenkov cone. Detector axis in the beam - y axis plane, at angle 45 deg in respect to the beam. Dustins plots

15. Status of the detector construction - Most of the parts for detector heads are ready - The design of the detector assembly is finalized, drawings are in the final stage and in the next few days will be given to the machine shop - PMTs are purchased - PMT bases must be modified to be able to accommodate -2000V, out of 9 bases 4 are ready - Quartz and movers are ordered

16. Other tasks - Setup for measurements of gains of all PMTs by single photon counting is ready, we are still waiting for return of CAEN ADC from repair in Italy - Blue LEDs are purchased and will be mounted in the detector heads for in beam monitoring of PMT linearity

17. Issues The most serious problem is uncertainty in delivery time of ordered quartz blocks. They should be delivered before the end of February, however, the manufacturer informed us that there will be a delay caused by bandsaw failure. The projected delivery time is now the beginning of the second week of March. For any case we are preparing four 13.4 cm long pieces of quartz, each made from 6 smaller pieces.