1. KOPIO meeting, T. Nomura (Kyoto U.)
Catcher
Scope of subsystem
Current specification from physics
Current design
Open issues
Resources
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

2. KOPIO meeting, T. Nomura (Kyoto U.)
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 “catcher”
Lead and acrylic slab sandwich counter near the beam named “guard counter”
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

3. KOPIO meeting, T. Nomura (Kyoto U.)
Scope of subsystem
aerogel
flat mirror
Cerenkov light
lead sheet
5inch PMT
Module
funnel
CATCHER
Lead and aerogel tile counter
Avoid detection of slow particles from neutron interactions
Distributed arrangement
Coincidence along the beam helps us catch forward g only g
red: e+/e-, blue: photon
Photon’s EM shower in the module array
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

4. Current specification from physics
Photon Efficiency
Energy spectrum of photons which go into the catcher after canonical kinematical cuts (Kp2; dominated by odd pairing events)
>98% for 300MeV photons
>99% for more energetic ones
Sensitivity to neutrons, KLs
To avoid false vetoes by beam neutrons and surviving KLs…
<0.3% for neutrons with Ekin=800MeV
KL decaying in the catcher ends up to be detected, but false veto probability should be kept less than a few %
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

5. Current design Overview
Guard counter
Catcher
beam
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

6. Current design of a module Elements / Optics
Parameters of each module
To get more Cherenkov lights
To simplify optics for easy production
TDR
Current
Aerogel
5cm-thick
20cm sq.
30cm sq.
n=1.03
(SP-30)
n=1.05
(IY-46)
Mirror
Parabolic
Flat
PMT /
Funnel
5-inch dia. PMT
Winstone-type cone
Inclined
Upright
TDR design
Current design
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

7. Current design of whole catcher Configuration
Distributed arrangement
Module size: 30cm x 30cm
Pb converter: 2mmt per layer
Number of modules: 370
10-20 in horizontal with beam divergence
25 layers along beam (8.3 X0 in total)
Z gap between layers: 35cm
Coincidence condition
>= 4 p.e. in 1st layer (A)
>= 2 p.e. in 2nd layer (B)
Top view
Line from opp. edge at the end of DV
Beam envelop
12m downstream of main detector
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

8. KOPIO meeting, T. Nomura (Kyoto U.)
Expected performance with current design Photon efficiency / Neutron sensitivity
Average over +/- 10cm(y), normal incident to Catcher
Photon efficiency
Photon energy (GeV)
0.2
0.4
0.6
0.8
1.0
1.2
300MeV 95 90 85
100
Neutron sensitivity
0.8GeV
Neutron energy (GeV)
0.5
1.0
1.5
2.0
2.5
3.0
10-2
10-3
10-4
10-5
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

9. Expected performance with current design Efficiency map
Efficiency as a function of incident position
Eg=300MeV
Incident angle depending on position (gs from downstream end of DV)
Beam core
@ Catcher front
X position dependence
Y position dependence
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

10. Current design 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
2 modules along the beam
Number of modules: 96
Side View
beam
Front View
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

11. KOPIO meeting, T. Nomura (Kyoto U.)
Expected performance with current design Efficiency map with guard counter
Efficiency as a function of incident position
Eg=300MeV
Incident angle depending on position (gs from downstream end of DV)
Y position dependence
Beam core
@ Catcher front
Catcher + Guard
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

12. Justification of the conceptual design Prototypes so far
1/4 size, flat mirror
light yield
Prototype 2 (2002-3)
1/4 size, parabolic mirror
response to proton (as substitute for neutron)
Check single layer eff. / two-layers’ coincidence
Good agreement with MC (with gas scintillation)
PT1
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

13. Issues Harmful influence of beam particles
False vetoes due to neutrons, KLs
Catcher size: 1.5 times larger than TDR design
False veto prob. also increases
Sensitivity to KL including
Decay in front of the catcher
Decay in the catcher  dominant
Interactions in the catcher
n flux
Flux*sensitivity
integrated
TDR
Current
By neutron
1.8%
3.0%
By KL
1.2%
2.4%
assuming DT (time window)=2ns
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

14. Issues Harmful influence of beam particles
Blindness by prompt photons, early neutrons and KLs
Possible to hide photons of background decays
Need double pulse separation by a waveform digitizer
How can we separate them? What resolution?
Seriousness of prompt photons depend on their energy
Need photon spectrum and yield with a spoiler in the beam
High counting rate by neutrons
PMTs of the catcher will suffer from high rate signals
Need a stabilized base
False veto, counting rate of the guard counter
Must be evaluated with halo yield and spectrum
All the above issues highly depends on the production angle
No margin now.
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)

15. Resources Manpower and funds
Kyoto University
N. Sasao (subsystem manager) : a bit
T. Nomura : 60-70%
Graduated students : 100% H. Morii, H. Yokoyama, T. Shirai, N. Taniguchi, + (1 or 2)
Other institutes in Japan
R. Takashima (Kyoto U of Education), M. Kobayashi (KEK), …
Fund in JFY2004 plan to make a full-size prototype
Japan-US: 45k$ approved
Grant-in-aid for the priority area: 240k$
May 14, 2004
KOPIO meeting, T. Nomura (Kyoto U.)