Catcher

1
Catcher

• Scope of subsystem
• Current specification from physics
• Current design
• Open issues
• Resources

2
Scope of subsystem

• Photon veto inside/near the beam at downstream
  end
• TASK
• Detect photons from KL decays passing through the
  beam hole
• Be insensitive to a vast amount of unwanted
  neutrons
• SOLUTION ? Utilize Cherenkov radiation
• Lead and aerogel tile sandwich counter inside the
  beam named aerogel catcher
• Lead and acrylic slab sandwich counter near the
  beam named guard counter

3
Specification from physics

• Photon Efficiency
• Energy spectrum of photonswhich go into the
  catcher after canonical kinematical cuts(Kp2
  dominated by odd pairing events)
• gt98 for 300MeV photons
• gt99 for more energetic ones
• Sensitivity to neutrons, KLs
• To avoid false vetoes by beam neutrons and
  surviving KLs
• lt0.3 for neutrons with Ekin800MeV
• KL decaying in the catcher ends up to be
  detected,but false veto probability should be
  kept less than a few

4
Current design Overview
Guard counter
Aerogel Catcher
beam
5
AEROGEL CATCHER Principle of aerogel catcher

• AEROGEL CATCHER
• Lead and aerogel tile counter
• Avoid detection of slow particlesfrom neutron
  interactions
• Distributed arrangement
• Coincidence along the beamhelps us catch forward
  g only

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AEROGEL CATCHER Module - Elements / Optics

• Parameters of each module
• To get more Cherenkov lights
• To simplify optics for easy production

TDR design
Current design
7
AEROGEL CATCHER Configuration

• Distributed arrangement
• Module size 30cm x 30cm
• Pb converter 2mmt per layer
• Number of modules 420
• 12-21 in horizontal with beam divergence
• 25 layers along beam(8.3 X0 in total)
• Z gap between layers 35cm
• Coincidence condition
• gt 4 p.e. in 1st layer (A)
• gt 2 p.e. in 2nd layer (B)

Beam envelop
Top view
12m downstream of main detector
8
Expected performance of AEROGEL CATCHER Photon
efficiency / Neutron sensitivity

• Average over the whole position and angle

Neutron sensitivity
Photon efficiency
gt99 _at_ 300MeV
0.3 _at_ 0.8GeV
9
GUARD COUNTER Principle of guard counter

• GUARD COUNTER
• Lead and acrylic slab counter
• Slow particle doesnt emit Cherenkov light
• Utilize the total reflection angle in light
  transportation
• Cherenkov lights from slow particlesdont
  fulfill the total reflection condition

Photon
Neutron
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Current design of GUARD COUNTER Guard counter

• Counter to cover the halo region
• Soft but many neutrons around the beam
• Lead acrylic slab sandwich
• Size 15cm x 15cm
• 8 layers of 2mm Pb 10mm acrylic
• Read by 5 inch PMT
• 3 modules along the beam
• Number of modules 144

Side View
beam
Front View
Module
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Expected performance of WHOLE CATCHER SYSTEM
Efficiency map of catcher guard counter
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Justification of the conceptual design
Prototypes so far
PT2

• Prototype 1 (2001-2)
• 1/4 size, flat mirror
• light yield
• Prototype 2 (2002-3)
• 1/4 size, parabolic mirror
• light yield
• response to proton (as substitute for neutron)
• Check single layer eff. / two-layers
  coincidence
• Good agreement with MC(with gas scintillation)

PT1