marco musy infn and university of milano-bicocca pylos, june 2002 aerogel as cherenkov radiator for...
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Marco MusyMarco Musy
INFN and University of Milano-Bicocca
Pylos, June 2002
Aerogel as Cherenkov radiatorAerogel as Cherenkov radiator for RICH detectorsfor RICH detectors
The LHCb experimentThe LHCb experiment
Particle IDneeded between1-150 GeV/c
Proton-protonProton-proton interactions at √s = 14 TeV at LHC
Two RICHsystems with3 Cherenkovradiators
Acceptance: 10-300 mrad (bending plane)
10-250 mrad (non-bending plane)
RICH1
RICH1
RICH2
RICH2
Local Luminosity 2 x 1032 cm-2s-1
3
Momentum
LHCb RICHes detectors
LHCb RICHes detectors
RICHRICH22 RICHRICH11
m RICHRICH11
Aerogel as Cherenkov radiator
Aerogel as Cherenkov radiator
• Light, solid quartz-like structure SiO2
• Physical properties: low density, = 0.15 g/cm³ n = 1.01 ÷ 1.10,
(n = 1 + 0.20)
A = 95.88 ± 0.04, C = (6.44 ± 0.01) 10ˉ³ μm¯4 /cm A = 91.97 ± 0.05, C = (7.22 ± 0.01) 10ˉ³ μm¯4 /cmA = 88.18 ± 0.06, C = (6.95 ± 0.01) 10ˉ³ μm¯4 /cm
Novosibirsk
tile 10x10 cm²tile 7x8 cm²tile1 + tile2
Aerogel type :• Novosibirsk, Boreskov Institute of Catalysis, Russia (hygroscopic)
• SP30 Matsushita Electric works Ldt, Japan (hydrophobic) T = A e-Cd/4
A is the long transmittance
C is the clarity coefficient
8cm
Ageing tests with γAgeing tests with γ 60Co (E= 1.3 MeV, 1.7 MeV)
Dose : 420 rad/min
1 year LHCb operation
Ageing tests with protonsAgeing tests with protons
Source of radiation: Proton beam 24 GeV/cFlux : 9 109 p/cm2/s Spot size : 2 x 2 cm2
Depletion in Transmittance of ~1% after 1 year run(w.r.t. non irradiated sample taken as a reference)
13
Humidity testsHumidity testsExpose hygroscopic aerogel tile to humid air (70%)
Measure water absorption through weight
Measure Transmittance in range 200-800 nm
Loss of 30% at 300 nm Loss of 15% at 400 nm Loss of 8% at 500 nm
TestTest beam Set-up at CERNTestTest beam Set-up at CERN
Beam from CERN-PS: πˉ and p/π in the range 6 – 10 GeV/c (Δp/p = 1%)
Quantum Efficiency of the 4 photocathodes > 20% (=280-380nm)
• Bialkali photocathode, K2CsSb• Fountain shaped electric field, demagnification factor ≈ 2.3• Silicon pad sensor 2048 pixels (16 sectors x 128 pads 1x1 mm² 2.3x2.3 mm² granularity on ph.cathode)
Hybrid Photo Detectors
Hybrid Photo Detectors
AEROGEL test beam
Aerogel
Glass filter
Place holder
Rayleigh scattering Refraction on the boundaries Light absorption Light detection on photocathode Photocathode transparency...
All relevant processes are considered in the simulation:
Beam axis
photons
Geant4
Aerogel tile
Mirror
Photo Detectors
Silicon layers
Monte Carlo Monte Carlo descriptiondescriptionMonte Carlo Monte Carlo descriptiondescription
Sector #4
Sector #8
Ring region
Out of ring
sect 4
sect 8
Test beam resultsTest beam resultsTest beam resultsTest beam results• 9 Gev/c π¯ beam• 4 cm aerogel Novosibirsk• noise/pad < 2%
Photoelectron yieldPhotoelectron yieldPhotoelectron yieldPhotoelectron yield
Number of ph.electrons
Novosibirsk4 cm aerogel8 cm aerogel
On ring
• Integrate signal across the measured arcs and compare with Monte Carlo• Evaluate nr. photoelectrons: - on ring, |R-R| < 3σ - out of Cherenkov ring
Novosibirsk No filter
Filter D263
4 cm 8.3 ± 0.310.0 ± 1.1
5.6 ± 0.26.4 ± 0.7
8 cm10.7 ± 0.412.9 ± 1.1
8.4 ± 0.38.9 ± 1.0
Photoelectron yield Photoelectron yield cont’dcont’dPhotoelectron yield Photoelectron yield cont’dcont’d
Contributions to total error:• background subtraction (±1σ): ~ 5%• inefficient or noisy pads : ~ 4%• definition of ‘active region’ (±1mm): 2%• separation of on-ring/off-ring (±2mm): 3%• signal losses outside ADC thresholds (±1σ): 3%
DataMC
results are normalised to 2π acceptance
on-ring
off-ring
Npe
8 cm
4 cm
8 cm
4 cm
No filterD263
4 cm(off-ring)
1.00 ± 0.100.81 ± 0.08
0.57 ± 0.040.55 ± 0.04
8 cm(off-ring)
1.10 ± 0.101.06 ± 0.11
0.94 ± 0.070.84 ± 0.10
results are in units of 10¯²/cm²
Ring reconstructionRing reconstruction
Thickness No filter Filter D263 Glass
θc σθ θc σθ θc σθ
4 cm 250.0 5.4248.7 4.0
247.1 5.0246.8 3.0
243.6 5.3243.2 3.8
8 cm 246.8 5.8245.0 3.9
245.4 4.8243.7 3.0
246.0 5.3 --
6 cm 250.2 8.7 250.9 5.8 251.3 5.4
8 cm 249.5 9.8 250.3 6.2 --
Data
MC
Data
Novosibirsk
Matsushita
rad
• Study resolution as a function of - filter type - aerogel thickness - aerogel type
• Results per single photoelectronsingle photoelectron are (mrad):
-- Data-- Monte Carlo4cm Novosibirsk (no filter)
θc
Ring reconstruction Ring reconstruction cont’dcont’d
• Contribution to angular resolution is determined with the simulation:
• Resolution is expected to scale as A/√N + k (in the 3σ ring region)
Sourceσ (mrad)
Pixelling 1.3
Chromaticity 2.5
Point spread func.+ Emission point
1.1
Beam divergence
0.7
Allignement 2.2
TOTAL 3.8
-- Fit to data
Resolutions differ by ~20-40% in MC with respect to the Data.Still under investigation.
/p separation at
PID performancePID performance
8 GeV
8 GeV
6 GeV
10 GeV
rad
SINGLE ph.e.
6.1
4.8
3.1
θ
~30,000 events
PID performance cont’dPID performance cont’d
• Evaluate separations Nσ = Δθ/σθ, scaling with the Npe and extrapolate to the total acceptanceEnergy θp θπ Nσ
6 GeV194.0±7.8
243.6±2.9
9.3
8 GeV216.4±4.1
244.3±2.8
8.1
10 GeV224.8±3.0
242.8±2.3
6.8
π-ring
p-ring
Clear π/p separation
• For 4 cm aerogel + filter:
ConclusionConclusion The use of aerogel as Cherenkov radiator has
become reliable in high energy particle physics
Test beam has shown a photon yield which agrees with the Monte Carlo expectations
Good PID ability in the momentum range 6 – 10 GeV/c
Further studies are on the way