Design Studies for a Compact Tungsten Scintillator Electromagnetic Calorimeter

C.Woody, S.Cheung, J.Haggerty, E.Kistenev, S.Stoll

For the PHENIX Collaborationand

Brookhaven National Lab

N29-22011 IEEE NSS/MIC

Valencia, Spain

October 26, 2011

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What do we mean by “Compact Calorimetry” ?

Compact implies:• showers have limited extent in both transverse and longitudinal dimensions (ideally would like showers to be point-like)• calorimeter is physically small ( dense) so that it occupies a minimal amount of space

To achieve this, one requires:• Small Moliere radius• Short radiation length

However, there is a tradeoff between “compactness”and energy resolution (determined by the sampling fraction and photostatistics)

Material Pb WRM (mm) 16.0 9.3

X0 (mm) 5.6 3.5

C.Woody, 2011 NSS N29-2, 10/26/11

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The Present PHENIX Experiment

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The Transformation to sPHENIX

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The sPHENIX Detector

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Calorimeter Simulation (GEANT4) Energy Resolution vs Sampling Thickness

Absorber (X0) a (%) (√ GeV) b (%)

0.25 7.6 ± 1.7 0.3 ± 1.0

0.50 12.0 ± 1.8 0.3 ± 1.0

1.0 18.1 ± 1.8 0.4 ± 1.0

2.0 25.5 ± 2.0 1.2 ± 1.1

3.0 40.8 ± 2.3 2.8 ± 1.2

= + b

Moliere RadiusRM = 21.1 MeV ~ 2.6 X0 9.3 mm for W

Approximately 90% of energy is contained within 1 RM, nearly independent of E

( a only includes sampling fluctuations, 1.5 mm scintillator plates )

sPHENIX requires 15%Want small photostatistics contribution to the overall resolution

1 X0 (3.5 mm) W1.5 mm scint30 % scint by volume3.7% energy fraction

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Preshower and Longitudinal Segmentation

Preshower Compact EMCAL (~ 15 X0)

Hadronic Calorimeter

Superconducting

Magnet(~ 1X0)

Longitudinal segmentation required for:• g/p0 separation for single g and jet measurements up to pT ~ 40 GeV/c

• e/p separation (~ 10-3) for measuring J/Y’s and U’s

p0

g

• ~ 3-4 X0 Silicon-Tungsten• ~ 2 mm W plates, ~ 1 mm Si strips → See NP5.S-180 (E.Kistenev) Preshower

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Compact EMCAL for sPHENIX

Three designs being considered:• Optical Accordion• Projective Shashlik• Scintillating Fiber (SciFi)

Requirements:• Compact• Projective• Hermetic• Readout works in magnetic field• Low cost

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Optical Accordion

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• Volume increases with radius• Scintillator thickness doesn’t increase with radius, so either tungsten thickness must increase or the amplitude of the oscillation must increase, or both• Plate thickness cannot be totally uniform due to the undulations• Small amplitude oscillations minimize both of these problems

• Optical readout with either scintillating fibers or scintillating plates with embedded wavelength shifting fibers• Fibers read out with SiPMs or APDs

Needs to be hermetic and projective

Accordion design similar to ATLAS Liquid Argon Calorimeter

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Accordion Shaped Tungsten Plates

Tungsten Heavy Powder, Inc (San Diego, CA)

• Sintered from tungsten powder• Final density ~ 17.5 g/cm3

• Shape and thickness variation not a problem• Fibers can be glued in between plates with tungsten/epoxy composite (density ~ 10-11 g/cm3)

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Light Output of Scintillating Fibers with SiPM

SiPM

Trigger pmtFibers

90Sr source

MPPC

PMT2

PMT3trigger

Sr90 source above

single 1mm square scint fiber, read out w/ SiPM. 12cm fiber, Sr-90 source at midpoint, Fiber scint trigger (pmt)

pe

0 10 20 30 40 50

coun

ts

0

2000

4000

6000

8000

10000

12000

trigger fiber in backgaussian fit

fit mean: 16.1 peLight output ~16 p.e./0.2 MeV ~ 80 p.e./MeV

Challenge is to collect all this light onto a relatively small area SiPM or APD.

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Light Output of Scintillating Tiles + WLS Fibers + SiPM

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Light output with ~ 25 p.e./MeV with looped fibers

Advantage of fewer fibers compared with pure scintillating fiber design

Possible readout using scintillatingplates and WLS fibers

SiPM

WLSfibers

Scinttile

stack of 5 IHEP scintillator tiles (60x48x2mm) with 1mm deep machined grooves. 1mm wls fibers in grooves, read out with 3x3mm SiPM

pe/MeV

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60

coun

ts

0

2000

4000

6000

8000

10000

12000

14000

16000

3 fiber loops - 24.5 pe/MeV6 individual fibers - 13.2 pe/MeV

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Projective Shashlik

• Size of absorber and scintillator plates would both increase as a function of depth • Small size improves light collection • Fewer fibers to collect light onto a SiPM or APD

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Light Output of Scintillating Tiles + WLS Fibers + SiPMShashlik Configuration

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SiPM

Trigger pmtTile stack

137Cs source

Measured scintillation light from 3cm stack of IHEP 22x22x1.5mm scintillator tiles (~1.2mm diam. holes). With Tyvek separators between tiles. Collimated Cs-137 source. Read out through 1-5 wls fibers and a 3x3mm MPPC.

number of readout wls fibers

0 1 2 3 4 5 6

<pe/

MeV

>

0

2

4

6

8

10

12

14

16

1.2 mm diam fibers1.0 mm diam fibers1.0 mm diam fiber loops

center hole

corner hole

Tile

stack of 22x22x1.5mm scint tiles with wls fibers1.2mm diam fibers (Kuraray Y-11)

pe/MeV

0 5 10 15 20 25 30

coun

ts

0

1000

2000

3000

4000

5000

6000

7000

1 fiber - 3.0 pe/MeV5 fibers - 11.8 pe/MeV

Light output depends linearly on number of fibers

~ 12 p.e./MeV with 4-5 fibers

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Summary

C.Woody, 2011 NSS N29-2, 10/26/11

• Both physics requirements and cost limitations drive the need for highly compact calorimeters in future collider experiments.

• We believe a highly segmented optical readout tungsten-scintillator calorimeter can meet those requirements.

• Several calorimeter configurations have been studied that appear to be able to be able to meet those needs.

• Work will continue to develop one or more of these designs into a working prototype for beam testing next year.