Upstream Photon Veto (UPV)

UPV

Paul Eugenio

Florida State University

.

Main Objective

The UPV is a photon detector directly upstream of the hydrogen target

Its function is to detect backward-going photons by summing energy deposition in the backward direction

upstream

region

135o

12o

Barrel Calorimeter

LGD

Beam

Soft Photon Backgrounds

180 140 100 60 20

6

4

2

0

Eg

180 140 100 60 20

1

0.2

0

0.6

0.4

0.8

Eg

UPV

BCAL

L

UPV

BCAL

L

Photon Decay Angles

Photon Decay Angles

10%

½%

Soft Photon Energy Spectrum

Eg

20 40 60 80 100 120 140 160

MeV

50

200

150

100

0

Events/ 9MeV

Beamline Related Backgrounds

muon flux [/sec/cm2]

radial distance

cm

R.T. Jones et al. GlueX-doc-60-v1 (2003/2004)

Geant simulation of beamline and shielding including photo-hadronic interactions and muon pair production.

Conclusion:

negligible background

~25 kHz whole region

Design Options

Sampling Calorimeter

Benefits of design choice

fast detection (10-20 nSec)

good photon detection

good energy resolution

Benefits of design choice

good photon reconstruction

good energy resolution

good position resolution

Homogeneous Calorimeter

pointing crystal design

Disadvantages

increase complexity

slower detection(102-103nSec)

significant increase in cost

lead-scintillator sandwich

Disadvantages

coarse photon reconstruction

Advantages

relatively simple design

low cost

Veto Design Choice

Alternating lead/scintillator layers

18 layers of 1cm thick scintillator

First 12 layers of 0.185 cm thick lead sheets (0.36X0 each)

Remaining 6 layers 0.370 cm thick lead sheets (0.72X0 each)

Total thickness: 22.4 cm or 8.91X0

24% sampling fraction

Lead/Scintillator Sandwich

g

GEANT Simulations

~24% sampling fraction

independent

of energy

Response to

50 MeV photons

active

layers

passive

layers

GEANT Detection Efficiency

# of Pb/Scint. layers

10 15 20 25

40%

60%

100%

10 MeV

20 MeV

50 MeV

100 MeV

125 MeV

80%

efficiency

12+26

layers

Events were accepted if the visible energy exceeded a threshold of 2.0 MeV

GEANT Resolution

0	0.05	0.1	0.15	0.2	0.25

40%

60%

20%

25 MeV

50 MeV

75 MeV

100 MeV

Resolution

R & D Prototyping

Veto Prototype

Measure prototype performance in a low energy electromagnetic beam and compare results to GEANT4 simulations.

Instrument to test the building technique

Build infrastructure in place for future R&D w/ final goal of the construction of the UPV

Prototype has been constructed and initial testing is well underway. The study of prototype performance in a low energy beam (Ee- < 50 MeV) is planned by the end of 2004.

18 layers of 1 cm scint. interleaved with first 12 layers of 2.2mm lead then 6 layers of 4.4mm lead

Segmentation Options

Each scintillator layer is divided into 7-34 cm sections (238 cm x 238 cm scintillator plane)

Light collection is realized at one end of each section only

Every 3rd scintillator layer is readout in one orientation

x, u, v readout orientations

We are presently studying alternative segmentations

increased/variable lateral segmentation

3-sided -vs- 2-sided

Detector Readout

The UPV readout is almost the same as the BCAL

FADCs but no TDCs

The UPV will use the same technology

Various options are being explored

WSB light redirection

Clear fibers

WS fibers

Signal Electronics

Light Collection

Conclusions

The UPV is designed to tag	soft photons by summing the energy deposition in the backward direction

The UPV together with the BCAL & LGD form a near hermetic photon detection package

A lead-scintillator sampling design provides good detection at modest costs

R & D continues with focus to optimize performance , costs, and ease of construction

25 MeV

75 MeV

100 MeV

Prototype ADC Spectrum

Spectrum trigger

by opposite PMT

UPV Prototype Construction

2003-12-08T11:49:12