PREx detectorsPREx detectors
Progress reportProgress report
Krishna KumarKeith Otis
UMass
Piotr DecowskiSelamnesh Nida
Smith CollegeCollaboration Meeting, May 17-18,2007
Shielding
Drive
Light guide + PMT Quartz-tungsten stack
Shielding
Thin Quartz
Light guide + PMT
HRS focal plane
Keith Otis, UMass
Requirements:
1. Integrating2. Radiation hard (~1 GHz)3. Good resolution (<25%)4. Small size
Thin detector:
Challenges:PM output signal per one electron passing the detector:
€
Q e = N Ph←e ⋅N PE←Ph ⋅g Q←PE
Relative error:
€
δQ e = (δN Ph←e )2 + (δN PE←Ph )2 + (δg Q←PE )2
Simulations Binominal distribution
€
1− QE
NPh
€
(δgPE →Q )2
QE ⋅NPh
Relative statistical error of the parity violating asymmetry:
€
~1
NPh
€
1
Ne
1+ (δQ e )2
To minimize we have to maximize and
€
δQ e
€
N Ph
€
QE
For we need
€
δQ e < 0.25
€
NPh >~ 40
However:
For ( ) and expected rate of
electrons ~1 GHz, the current at the PM output will be:
€
QE ≈ 0.25
€
NPE >~ 10
€
I(μA) >1.6 ⋅10−3 g
We need a very low gain, linear tube!
Thin Quartz Detector
Concept:
quartz
conical mirror
tube mirror
PM
15 cm
4 cm*4cm 2”&3”
Optimization: -- cone length (mirror angle) -- quartz thickness -- quartz position in the cone -- PM diameter (2” and 3”)
Electron energy 850 MeV
Cone length (5 mm quartz)N
umb
er o
f ph
oto
ns
rea
chin
g P
M
Rel
ativ
e w
idth
of
dis
trib
utio
ns
6 cm6 cm
39
.1622 in
ch P
M d=2mm
d=5mmd=5mm
d=10mm
d=10mm
d=2mm
50
7 cm
7 cm
.14Optimal choice: 2 inch PM, 6 cm cone, d = 2 mm
3 in
ch P
M
Cone length (cm) Cone length (cm)
Quartz thicknessA
vera
ge
num
ber
of
pho
ton
s at
PM
Rel
ativ
e w
idth
of
dis
trib
utio
n
Quartz thickness (mm)
2 inch PMpeak width
rms of full distribution3 inch PM
5 m
m 5 m
m
onset of showering4 mm 15 mm
Optim
al ch
oice:
5 m
m q
uartz
bloc
k
Optimal detector parameters:
Trapezoidal quartz block 0.5cm thick, 4cm*4cm upper surface
Cone mirror 6 cm long, with quartz block positioned at the smalleropening of the cone
2 inch diameter PM
Simulated performance: NPh ~ 40, NPh ~ 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%)
Design concept
Cone mirror
to PM
Tube mirror
Realization
Cone
Quartz holder
Quartz
Front tube
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)
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