scintillator-based hadron calorimetry for the ilc/sid international linear collider workshops...

Scintillator-basedScintillator-basedHadron CalorimetryHadron Calorimetry

for the ILC/SiDfor the ILC/SiD

International Linear Collider WorkshopsSnowmass, 14-27 Aug, 2005

Dhiman Chakraborty

ILCW2005, Snowmass Scintillator-based HCal for ILC Dhiman Chakraborty

2

Why (not) scintillators?Why (not) scintillators?• Tested and true, well understood & optimized,

• New developments in cell fabrication & photodetection help meet ILC/PFA demands – Fine segmentation at a reasonable cost

– Photodetection and digitization inside detector ⇒min. signal loss/distortion, superior hermeticity

• Can operate in both analog and digital modes– Measures energy, unlike RPC & GEM that only offer

hit-counting (“tracking” or “imaging” calorimetry)

– Remains a viable option if digital PFA fails to deliver.


3

Design Considerations: Design Considerations: PFAPFA

• Need ≲10 cm2 lateral segmentation.

• At least ~35 layers and ~4λ must fit in ~1 m along R.

– Min. Rin driven by tracker performance.

– Max. Rout limited by magnet and material costs.

– Min. absorber fraction limited by the need for shower containment.

• ⇒2 cm thick absorber layers if SS (less if W).

• ⇒0.6-0.8 cm sensitive layers must respond to MIPs with good efficiency and low noise.

(cont’d...)


4

Design Considerations: Design Considerations: PFAPFA

(…cont’d)

• Good lateral containment of showers is important for minimizing the confusion term.

• W absorber in ECal ⇒ e/ compensation is not built in ⇒ must be achieved in software ⇒ particle id (inside calorimeter by shower shape?) may be important.


5

Design Considerations: Design Considerations: OthersOthers

• The technology must be – Reliable,

– Mechanically sound,

– Operable inside strong (~4.5T) magnetic field,

– Capable of 15+ years of running,

– Tolerant to ~5 fluctuations in T, P, humidity, purity of gas (if any). Monitoring will be necessary if response depends strongly on any of these,

– Suited for mass-production and assembly of millions of cells in ~40 layers,(cont’d…)


6

Design Considerations: Design Considerations: OthersOthers

• The technology must be (…cont’d)

– Allow hermetic construction (minimum cracks/gaps)

– Safe (HV, gas, …),

– Compatible with other subsystems (MDI?),

– Amenable to periodic calibration,

– Able to handle the rates (deadtime < 0.1 s?)

– Cost-effective (including construction, electronics, operation).


7

Hardware testsHardware tests

Cells made of cast (Bicron) and extruded scintillators (NICADD/FNAL) have been extensively tested with many variations of

– Shape (hexagonal, square),

– Size, thickness

– Surface treatment (polishing, coating),

– Fibers (manufacturer, diameter, end-treatment)

– Grooves (shaped, straight)

– Photodetectors (PMT, APD, SiPM, MRS)


8

Hardware testsHardware tests• Different cell and groove shapes with extruded and

cast scintillators


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Hardware Prototypes (DESY Hardware Prototypes (DESY “MiniCal”)“MiniCal”)

•DESY 6 GeV e beam 2003-2004•108 scintillator tiles (5x5cm)•Readout with Silicon PMs on tile, APDs or PMTs via fibres

2 cm steel

0.5 cm active

DES Y, Hamburg U, ITEP, LPI, MEPHI, Prague


10

DESY “MiniCal” Test Beam DESY “MiniCal” Test Beam resultsresults

• Resolution as good as with PM or APD*

• Non-linearity can be corrected (at tile level)– Does not deteriorate

resolution – Need to observe

single photon signals for calibration

• Well understood in MC • Stability not yet

challenged

NIM A (2005)


11

Choosing the Optimum Choosing the Optimum ThresholdThreshold

Efficiency and Noise Rejection

0%

20%

40%

60%

80%

100%

120%

Number of MIPs

Pe

rce

nt

Efficiency

Noise Rejection

0.25 MIP threshold: efficient, quiet


12

Miscellaneous Miscellaneous MeasurementsMeasurements

Response ratios between types, glues, fibers,…

• Scintillator type: extruded/cast ≈ 0.7

• Optical glue: EJ500/BC600 ≈ 1.0

• Fiber: Y11/BCF92 ≈ 3.2– Y11 = 1 mm round Kuraray,

– BCF92 = 0.8 mm square Bicron

Extruded/cast (cost) ≈ 0.05


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Optimum parametersOptimum parameters• Shape: Hexagonal or Square• Thickness: 5 mm• Lateral area: 4 - 9 cm2

• Groove: straight• Fiber: Kuraray 1 mm round (or similar)• Fiber glued, surface painted• Scintillator type: Extruded

But a bigger question is the photodetector: PMTs are costly, bulky, won’t operate in B field. We have been investigating APDs, MRS, Si-PM…

Based on what we have learnt so far


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The Metal/Resistor/ The Metal/Resistor/ Semiconductor Photodiode Semiconductor Photodiode

(MRS)(MRS)• From the Center of Perspective Technologies & Apparatus (CPTA),

• Multi-pixel APDs with every pixel operating in the limited Geiger

multiplication mode & sensitive to single photon,

• 1000+ pixels on 1 mm x 1 mm sensor,

• Avalanche quenching achieved by resistive layer on sensor,

• Detective QE of up to 25% at 500 nm,

• Good linearity (within 5% up to 2200 photons)

• Immune to magnetic field,

• Radiation-tolerant.


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Study of MRS/SiPMStudy of MRS/SiPM• Determination of Working point:

– bias voltage,

– threshold,

– temperature

• Linearity of response

• Stress tests: magnetic field, exposure to radiation.

• Tests with scintillator using cosmic rays and radioactive source.


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Metal Resistive Semiconductors Metal Resistive Semiconductors (MRS)(MRS)

Typical pulseheight spectrum

Poduced by the Center of

Perspective Technologies &

Apparatus (CPTA)

B. Dolgoshein


17

SiPM SummarySiPM SummaryWe have conducted a set of measurements to illustrate the potential

use of Si photodetectors in High Energy Collider experiments in general, and for hadron calorimetry at the ILC in particular.

• Good MIP sensitivity, strong signal (gain ~O(106)),

• Fast: Rise time ≈ 8 ns, Fall time < 50 ns, FWHM ≈ 12 ns (w/ amp)

• Very compact, simple operation (HV, T, B,…),

• Each sensor requires determination of optimal working point,

• Noise is dominated by single photoelectron: a threshold to reject 1 PE reduces the noise by a factor of ~2500,

• The devices operate satisfactorily at room temperature (~22 ˚C). Cooling reduces noise and improves gain,

• Not affected by magnetic field (tested in up to 4.4 T + quench),

• No deterioration of performance from 1 Mrad of irradiation.


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SiPM prospects on the SiPM prospects on the horizonhorizon• Bigger SiPMs are under development

– 3mm x 3mm made, but require cooling to -40 C

– 5mm x 5mm thought possible

– cost increase: insignificant (CPTA), linear (H’matsu)?

• 5mm x 5mm may help us eliminate fibers– put the SiPM directly on the cells

– wavelength matching by n-on-p (sensitive to blue scint. light) or WLS film

– hugely simplifies assembly

• Better uniformity across sample with purer Si.


19

Simulation StudiesSimulation Studies

Steel 20mmPolystyrene 5mm

Scint HCal

Gas Geom1

Steel 20mm

Gas 5mm

Gas Geom2

G10

Glass 1mm

Gas 1mm

Geometries considered


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++ energy resolution as function energy resolution as function of energy for different (linear) of energy for different (linear)

cell sizescell sizes


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CompensationCompensation

• Cell counting has its own version of the compensation problem (in scintillators).

• With multiple thresholds this can be overcome by weighting cells differently (according to the thresholds they passed).

• In MC, 3 thresholds seem to be adequate.


22

++ energy resolution vs. energy resolution vs. energyenergy

Two-bit (“semi-digital”) rendition offers better resolution than analog


23

Nhit vs. fraction of Nhit vs. fraction of ++ E in cells with E in cells with

E>10 MIP:E>10 MIP: Gas vs. scintillatorGas vs. scintillator

2-bit readout affords significant resolution improvement over 1-bit for scintillator, but not for gas


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++ energy resolution vs. energy resolution vs. energyenergy

Multiple thresholds not used


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Non-linearityNon-linearity

• Nhit/GeV varies with energy.

• This will introduce additional pressure on the “constant” term.

• For scintillator, the non-linearity can be effectively removed by “semi-digital” treatment.


26

±± angular width: density angular width: density weightedweighted


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Simulation SummarySimulation Summary• Large parameter space in the nbit-

segmentation-medium plane for hadron calorimetry. Optimization through cost-benefit analysis?

• Scintillator and Gas-based ‘digital’ HCals behave differently.

• Need to simulate detector effects (noise, x-talk, non-linearities, etc.)

• Need verification in test-beam data.

• More studies underway.


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TB: Scint HCal layer TB: Scint HCal layer assemblyassembly


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SummarySummary• Simulations indicate (semi-) digital approach to be

competitive with analog calorimetry• Prototypes indicate scintillator offers sufficient

sensitivity (light x efficiency) & uniformity.• Now optimizing materials & construction to minimize

cost with required sensitivity.• SiPM and MRS photodetectors look very promising.• Preparations for Test Beam (Analog tile HCal and Strip

tail-catcher/muon tracker) are in full swing.

All-in-all scint looks like a competitive option.

We are moving toward the next prototype.


30

Thank you!Thank you!For further details, see talks given by DC at

• The LC study group mtg on 26 May ’05,

• The Beaune Photodetection Conference, 19-24 June ’05.

Links at

http://www.fnal.gov/~dhiman/talks.html


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Backup slidesBackup slides


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Working point determination with Working point determination with LEDLED

• The MRS is to able to separate single photoelectrons• Different response under identical setup ⇒ working point must be determined for each channel individually

0

500

1000

1500

2000

1 61 121 181 241 301 361 421 481

ADC Channels

Co

un

ts

Channel 2

0

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1 61 121 181 241 301 361 421 481

ADC Channels

Co

un

ts

Channel 4

0

250

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1 61 121 181 241 301 361 421 481

ADC Channels

Co

un

ts

Channel 5


33

Cosmic MIP detection with Cosmic MIP detection with SiPMSiPM

Comparable to PMTComparable to PMT


34

Noise Rate vs. Bias Voltage & Noise Rate vs. Bias Voltage & ThresholdThreshold

• The right end of the plateau region in the Figure on left is optimal for our purpose.

• For thresholds in the range of 80±10 mV and bias voltage in

50.0±0.5 V, the dark noise is well under control.

1

10

100

1000

10000

100000

1000000

10000000

48.5 50.5 52.5 54.5 56.5

Bias (V)

Fre

qu

ency

(H

z)

70mV

80mV

90mV

1

10

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1000

10000

100000

1000000

10000000

0 50 100 150Threshold (mV)

No

ise

(Hz)

52V

50.6V

49.6V


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Signal & Noise Amplitudes vs. Bias Signal & Noise Amplitudes vs. Bias VoltageVoltage

• For this particular device S/N peaks at Vbias≈ 52 V

• Sharp peaking in S/N⇒ working point must be found for each piece.

0

100

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300

400

500

600

700

48 50 52 54 56

Bias (V)

Am

plit

ud

e (m

V)

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48 50 52 54 56 58

Bias (V)

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ise

Am

plit

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V)

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48 50 52 54 56 58

0

5

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48 50 52 54 56 58

Bias (V)

S/N


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Temperature DependenceTemperature Dependence

• Bias = 51.3 mV, threshold = 80 mV

• Loss in signal amplitude with increase in T ≈ 3.5%/˚C

0

100

200

300

400

500

19.5 20.5 21.5 22.5 23.5 24.5 25.5Temperature (oC)

No

ise

(Hz)

y = -14.369x + 667.862/DoF=0.89

330

340

350

360

370

380

390

19.5 20.5 21.5 22.5 23.5Temperature (oC)

Sig

nal

Am

plit

ud

e (m

V)


37

Fiber Positioning on MRSFiber Positioning on MRS

Optimal fiber-sensor

mating is crucial.

0

0.2

0.4

0.6

0.8

1

1.2

2.5 3 3.5 4 4.5

Position, mm

Sig

nal

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0.8

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Distance from Sensor, mm

Sig

nal

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-3.5 -1.75 0 1.75 3.5

Angle, o

Sig

nal


38

Linearity of ResponseLinearity of ResponseSince the response of an individual pixel is not proportional to n,

(unless it has had time in between to recover), non-linearity is

expected when the detector receives a large number of photons.

Deviation reaches 5% (10%)

at n ≈ 2200 (3000) or,

nPE ≈ 550 (750).

One MIP ≈17 PE

⇒ up to 32 MIPs can be

measured within 5%

linearity.


39

Stress Tests: Effect of Mag. Stress Tests: Effect of Mag. fieldfield

No significant effect of fields up to 4.4 T and quenching at 4.5T


40

Stress Tests: Effect of Stress Tests: Effect of IrradiationIrradiation

• No detectable damage from 1 Mrad of y = 6E-05x + 12/DoF=0.857

0.92

0.94

0.96

0.98

1

1.02

1.04

1.06

1.08

48 50 52 54 56 58Bias (V)

Rat

io o

f F

req

uen

cies

y = -1E-05x + 12/DoF=0.851

0.95

0.97

0.99

1.01

1.03

1.05

0 40 80 120

Threshold (mV)

Fat

io o

f N

ois

e F

req

uen

cies

y = 3E-05x + 12/DoF=0.873

0.96

0.98

1

1.02

1.04

48 50 52 54 56 58

Bias (V)

Rat

io o

f S

ign

al A

mp

litu

des


41

Hit timingHit timing


42

Hit timing (contd.)Hit timing (contd.)


43

Hit timing (contd.)Hit timing (contd.)


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Hit timing (contd.)Hit timing (contd.)Scintillator

RPC

•Same Z→jj event at pole

•Same cell size (1cm x 1 cm)

•Same threshold of 0.25 MIP


45

Hit timing (contd.)Hit timing (contd.)ECal hits in the same events as on the last slide


46

Time of flightTime of flight

t (ns)

dN

hit/d

t


47

Time-of-flight dependence of Time-of-flight dependence of resolutionresolution

100ns/5s


48

Avalanche Photo-DiodesAvalanche Photo-DiodesHamamatsu APD gain vs V @ diff wavelengths (T= 18 ºC)

1.0

10.0

100.0

1000.0

100 150 200 250 300 350 400

Bias Voltage, V

Gai

n

486nm 565nm for 587nm 660nm

scintillator-based hadron calorimetry for the ilc/sid international linear collider workshops...

Documents

dhiman chakraborty slide

ilc dhiman chakraborty

contd slide

mrs slide

design considerations

thick absorber layers

digital pfa

sensitive layers