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