A General High Resolution Hadron Calorimeter using Scintillator Tiles
Scintillator-based Hadron Calorimetry for the ILC/SiD
description
Transcript of Scintillator-based Hadron Calorimetry for the ILC/SiD
Scintillator-basedScintillator-basedHadron CalorimetryHadron Calorimetry
for the ILC/SiDfor the ILC/SiD
International Linear Collider WorkshopsSnowmass, 14-27 Aug, 2005
Dhiman Chakraborty
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Why (not) scintillators?Why (not) scintillators?• Tested and true, well understood & optimized,
• New developments in cell fabrication & photo- detection 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.
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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...)
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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.
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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…)
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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).
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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)
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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
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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)
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Choosing the Optimum Choosing the Optimum ThresholdThreshold
Efficiency and Noise Rejection
0%
20%
40%
60%
80%
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120%
Number of MIPs
Pe
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Efficiency
Noise Rejection
0.25 MIP threshold: efficient, quiet
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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
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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.
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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.
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++ energy resolution vs. energy resolution vs. energyenergy
Two-bit (“semi-digital”) rendition offers better resolution than analog
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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.
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±± 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.
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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
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Cosmic MIP detection with Cosmic MIP detection with SiPMSiPM
Comparable to PMTComparable to PMT
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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.
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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.
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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
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y = -14.369x + 667.862/DoF=0.89
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Fiber Positioning on MRSFiber Positioning on MRS
Optimal fiber-sensor
mating is crucial.
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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.
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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
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Stress Tests: Effect of Stress Tests: Effect of IrradiationIrradiation
• No detectable damage from 1 Mrad of y = 6E-05x + 12/DoF=0.857
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Hit timingHit timing
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Hit timing (contd.)Hit timing (contd.)
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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
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Hit timing (contd.)Hit timing (contd.)ECal hits in the same events as on the last slide
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Time of flightTime of flight
t (ns)
dN
hit/d
t
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Time-of-flight dependence of Time-of-flight dependence of resolutionresolution
100ns/5s
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Avalanche Photo-DiodesAvalanche Photo-DiodesHamamatsu APD gain vs V @ diff wavelengths (T= 18 ºC)
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