Detectors for PREx

Collaboration Meeting, April 17-18, 2009

Piotr Decowski, Smith CollegeKrishna Kumar. UMass

January 2008 testDustin’s analysis

1cm thick quartz 0.5cm thick quartz

MPV = 25.48 GSigma = 5.65Net width = 5.34 (21%)Net RMS = 8.57 (34%)(5.34)2 = 28.5

MPV = 14.37 GSigma = 4.59Net width = 4.20 (29%)Net RMS = 5.49 (38%)(4.20)2 = 17.64

Pedestal width = 1.85

NPE = 1/(.21)2 = 22.7 NPE = 1/(.29)2 = 11.9

Statistics:

January 2008 testAbsolute determination of NPE:

NPE * (1.602*10-19 C)*PMTGain = MPV(ch)*(50*10-15C/ch)

LeCroy 1881M ADC

NEEDED!

Measurement of PMT gain Anna Boehle, Diana Jaunzeikare, Smith College

21 fC/ch

Measurement of PMT gain, cont PMT: Hamamatsu R7723Q (fused silica window)

PMT # ZK40033:

Gain @ -2000V = 4.384*105

Results

Statistics:

Absolute gain:

NPE = 22.7 NPE = 11.9

NPE = 18.1 NPE = 10.2

1cm thick quartz 0.5cm thick quartz

NPE (1cm)/NPE(0.5cm) = 1.90

NPE (1cm)/NPE(0.5cm) = 1.77 (exp)

Note: without pedestal width subtraction statistics gives NPE(1cm) = 20.3, and NPE(1cm) = 9.8

GEANT4 SimulationsJon Wexler, UMass

Quartz block

PMT cathode

Cone mirror Tube mirror

Simulations: photon energy range

185 nmQuartz cut

500 nmQE cut

380nmAlzak cut

Standard PMTQE cut

PMT QE:

Alzak: reflectivity 93 - 98%Anodized Al reflectivity: 85 - 87%

Simulations: results1cm thick quartz 0.5cm thick quartz

NPE = 22.7 NPE = 11.9

NPE = 18.1 NPE = 10.2

NPE = 26.6 NPE = 13.9Sim:

Stat:

Gain:

Simulations overestimate experimental results by ~ 30%(there is room for improvements!)

Simulations: Al vs Alzak1cm thick quartz 0.5cm thick quartz

Al

Alzak

NPE = 26.6 NPE = 13.9

NPE = 64.5 NPE = 34.0

Improvement: factor 2.4 !

HRS focal plane

Bob Michaels

Detector concept

10 c

m

Quartz 0.5cm (0.25cm) thickAl mirror tube

2” PMT

2” PMTOptimize

Optimize

Expected ~20 PEper PMT/electron(~4nA @1GHz)

Top view

Two stacked 0.25cm thick detectors?

LED

Detector configuration

e- beam e- beam

Det 1

Det 2A_T

Det

Conclusions and plan1. 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.