Catcher

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

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

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

4. Current specification from physics Photon Efficiency Energy spectrum of photonswhich 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 % KOPIO meeting, T. Nomura (Kyoto U.)

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

7. Current design of whole catcherConfiguration Top view 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) Line from opp. edge at the end of DV Beam envelop 12m downstream of main detector KOPIO meeting, T. Nomura (Kyoto U.)

8. Photon efficiency Neutron sensitivity 100 10-2 95 >99% @ 300MeV 90 10-3 0.3% @ 0.8GeV 85 10-4 10-5 0.5 1.0 1.5 2.0 2.5 3.0 0.2 0.4 0.6 0.8 1.0 1.2 Neutron energy (GeV) Photon energy (GeV) Expected performance with current designPhoton efficiency / Neutron sensitivity • Average over +/- 10cm(y), normal incident to Catcher KOPIO meeting, T. Nomura (Kyoto U.)

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

10. Current designGuard 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 KOPIO meeting, T. Nomura (Kyoto U.)

11. Beam core @ Catcher front Expected performance with current designEfficiency 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 Catcher + Guard KOPIO meeting, T. Nomura (Kyoto U.)

12. Justification of the conceptual designPrototypes 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 KOPIO meeting, T. Nomura (Kyoto U.)

13. n flux Flux*sensitivity integrated IssuesHarmful 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 assuming DT (time window)=2ns KOPIO meeting, T. Nomura (Kyoto U.)

14. IssuesHarmful 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. KOPIO meeting, T. Nomura (Kyoto U.)

15. ResourcesManpower and funds Manpower • 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$ KOPIO meeting, T. Nomura (Kyoto U.)