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)