Beam Catcher in the KOPIO experiment

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Beam Catcher in the KOPIO experiment
Hideki Morii (Kyoto Univ.) for the KOPIO
collaborations

• Contents
• What is Beam Catcher?
• Basic Design
• Expected Performance
• Aerogel Quality Control System

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Beam Catcher in the KOPIO experiment
1. What is Beam Catcher?

• KOPIO experiment measures KL -gt p0nn mode
• Identification Detect p0 and nothing
• 9 2g 9
  veto

Vetoing extra particle is predominant defense to
BG
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Beam Catcher
1. What is Beam Catcher?

• Photon veto which covers beam core region
• under high neutron rate
• 10GHz (gt10MeV)
• Need to be
• efficient to g rays 99 _at_ 300MeV
• inefficient to neutrons 0.3 _at_ 0.8GeV
• Aerogel Cherenkov
• distributed geometry
• suppress neutron efficiency

Catcher Module
Lead Converter
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Beam Catcher MC Event Display
1. What is Beam Catcher?
Event Display for g
Event Display for neutron
Top View
Top View
Side View
Side View
Secondary particles are created isotropically
Shower spreads forward
-gt Can distinguish g from neutron using geometry
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Design of Beam Catcher Single Module
2. Basic Design

• Lead converter
• Size 30 x 30 cm , 2mm thick
• Aerogel
• Size 30 x 30 cm , 5 cm thick
• Refractive index n 1.05
• Mirror
• flat mirror
• Funnel
• Winston cone type
• PMT
• 5 inch PMT

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Design of Beam Catcher - Configuration
2. Basic Design

• Tapered configuration
• 10 modules (front layer)
• 20 modules (back layer)
• 25 layers
• Number of modules
• 370 modules
• Coincidence condition

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Simulation Efficiency for g
3. Expected Performance

• Coincidence efficiency for g

vertical position dependence
beam size
efficiency
efficient region 7cm
Y position (cm)
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Simulation Insensitivity to neutrons (1)
3. Expected Performance

• Insensitivity to neutrons

number of false veto
coincidence efficiency for n
efficiency
neutron yield
coincidence count
neutron kinetic energy (GeV)
?2.8 false veto prob.
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Simulation Insensitivity to neutrons (2)
3. Expected Performance

• Single count rate by neutrons

?single rate 600kHz / module
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Aerogel Quality Control System
4. Aerogel Quality Control System
It is important to control optical properties of
aerogel

• (i) Transmittance
• LED (light source) PMT (photo detector)
• (ii) Cherenkov light Yield
• Solenoid Spectrometer (as b source) mirror PMT

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Setup for Transmittance Measurement
4. Aerogel Quality Control System (i)
transmittance

• PMT with 2mm hole mask detects LED light
• 30mm x 30mm area is scanned at 2mm interval
• by moving X-Y stage

Masked by black paper with a 2mmX2mm hole
UV,BLUE,GREEN, YELLOW,RED 5-COLORS
Aperture
Aperture
PMT on XY stage
Aerogel on X-Y stage

• position dependence of transmittance can be
  measured

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Transmittance -Rayleigh scattering-
4. Aerogel Quality Control System (i)
transmittance
Note that Rayleigh scattering is dominant in
Aerogel
The Tile with rough surface n1.03
The tile with Clean surface n1.03
transmittance
transmittance
A0.93 CT0.0088mm4
A0.82 CT0.0094mm4
Absorption also increase
l(nm)
?(nm)
Two parameters, A and CT, are used as the input
to our MC simulation . Can it predict correct
light yield?
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Measurement of Cherenkov Light Yield
4. Aerogel Quality Control System (ii) light
yield

• To measure Cherenkov light yield
• Solenoid Magnet Spectrometer
• b source gap type solenoid magnet
• Setup for light yield measurement
• Spectrometer mirror PMT

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Solenoid Magnet Spectrometer
4. Aerogel Quality Control System (ii) light
yield
b sourceGap-type Solenoid Magnet gt Spectrometer

• We can get monochromatic electron beam
• Variable Energy up to a few MeV
• Beam intensity of 30 Hz _at_2.5MeV

r
Concept of Electron trajectory in this magnet

• POINT
• TWO MAGNETS
• Large acceptance
• High Resolution
• parallel e- beam along Z-axis

IRON
Ru
COIL
Electron rotate by Bz
GAP
Magnetic Field is strong near the gap
0.8 m
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Spec of the Spectrometer
4. Aerogel Quality Control System (ii) light
yield
Energy spectrum of 106Ru with and without magnet
keV
Spectrum of focused electron
? data ? Expectation
A
keV
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Measurement of Cherenkov Yield by the
Spectrometer


4. Aerogel Quality Control System (ii) light
yield
Setup
Cherenkov image on PMT

• b source
• 106Ru(3.541MeV)

5inchPMT
MC
Two trigger Scintillators are placed downstream
of 10f hole at the mirror surface
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Cherenkov Yield Energy Dependence Measurement1
4. Aerogel Quality Control System (ii) light
yield

• We measure the Cherenkov light yield with
  changing the energy of electron

Example of the results for two aerogel samples
(thickness11mm) with similar transmittance but
different refractive index
n1.05 TR69_at_470nm
P.E
n1.03 TR67_at_470nm
P.E
? GEANT ? DATA
? GEANT ? DATA
Incident Energy of electron
Incident Energy of electron
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Summary
Summary

• Beam Catcher
• Photon detector positioned in neutral beam
• -gt Need to have enough g efficiency
• -gt Need to insensitive to neutrons
• Design
• Pb Aerogel Cherenkov counter with distributed
  geometry
• Expected Performance
• 99 _at_ 300MeV / 0.3 _at_ 800MeV -gt 3 false veto
  prob.
• Aerogel quality control system
• Transmittance
• Cherenkov light yield

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Extras
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Beam Catcher Prototype Test

• Light yield using p
• Neutron inefficiency
• - using proton in place of neutrons

Prototype Module
Light Yield
Proton Efficiency
Data matches MC very well
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Simulation Insensitivity to KL (1)
Coincidence efficiency for KL
False veto probability by KL
? 2.3 false veto prob.
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Simulation Insensitivity to KL (2)
Single count rate by KL
? single rate 330 kHz
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Cherenkov Yield Energy Dependence Measurement2
4. Aerogel Quality Control System
Example of the results for two aerogel samples
(thickness11mm) with the same refractive index
but different transmittance
n1.03 TR67_at_470nm
n1.03 TR85_at_470nm
P.E
P.E
1.9 P.E _at_2.4MeV
1.5 P.E _at_2.4MeV
? GEANT ? DATA
? GEANT ? DATA
Incident Energy of electron
Incident Energy of electron
A0.82 CT0.0094µm4
A0.94 CT0.0044µm4