1. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy1 KOPIO Beam Catcher Tadashi Nomura (Kyoto U.) Contents –What is Beam Catcher? –Concept and Design –Expected Performance –Proof of Principle –Summary

2. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy2 Veto detectors surrounding Decay Region Particles can escape through the beam hole Task K   experiment needs hermetic veto system Charged particles –Can be swept out from the beam and detected outside Photons –Must be detected inside the beam  Need “in-beam” photon detector Beam Catcher Signature = 2  + nothing

3. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy3 Challenge “In-beam” environment High intense beam (necessary to observe >100 K   ; Br~10 -11 ) –A vast amount of neutrons (~30G/spill in KOPIO)  Produce protons, pions, (  and e + /e - ) in the detector –Most KLs survive after decay region (~300M/spill)  Decay into , ,e + /e - in the detector  These secondary particles fire the counter and disturb its primary function !! Spill length ~ 5 sec

4. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy4 Solution Utilize Cherenkov radiation Aerogel tile (n=1.05) or Acrylic slab radiator  Avoid detection of slow particles from neutron interactions Slow , p and other hadrons cannot emit lights. Use direction information Segment the detector into many modules and require coincidence along the beam direction  Catch forward photons only Reduce fake signal due to  from secondary  0 (neutron interaction and K L decay in the detector)

5. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy5 Aerogel Catcher in Beam Converter (Lead) + Radiator (Aerogel tile) Sensitive area of 30cm x 30cm Like “Sandwich” detector by modules’ array aerogel flat mirror Cerenkov light lead sheet 5inch PMT Module funnel  red: e + /e -, blue: photon Example of  event (MC) Plan view Coincidence

6. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy6 Guard Counter in Halo Region Converter (Lead) + Radiator (Acrylic slab) Sensitive area of 15cm x 15cm “Sandwich” detector Total reflection condition in light transportation can reduce neutron’s signal –e + /e - emit large angle Cherenkov lights  meet the total reflection condition –Slow particles cannot emit light or generate only small angle emission which escape to outside of the slab Photon Neutron

7. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy7 KOPIO Catcher System In-beam Aerogel Catcher Module size: 30cm x 30cm Pb converter: 2mm per layer Number of modules: 420 –12-21 in horizontal with beam divergence –25 layers along beam (8.3 X 0 in total) Z gap between layers: 35cm Halo Guard counter Just before Aerogel Catcher ( 2mm Pb + 10mm Acrylic ) x 8 layers x 3 modules Top view 12m downstream of main detector Beam envelope

8. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy8 Location of Catcher System Beam Catcher Decay Region

9. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy9 Expected Performance by MC (1) Aerogel Catcher EfficiencyY position dependence 99% @ 300MeV Beam core

10. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy10 Expected Performance by MC (2) Hit probability for Neutrons 0.3% @ 800MeV Hit probability for K L s Dominated by decays in the Catcher

11. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy11 Signal Loss due to Catcher False Hit Accidental hit due to neutrons may kill K   signal Total false hit probability was found ~ 0.4 events /  -bunch –Integrated over the duration consistent with the arrival time of  from our signal K L If we set the time window to be 3ns, signal loss due to false hit will be 4.6% –Calculation based on random effect –Detailed studies by MC under way Neutron rate False hit (rate x hit prob.) False hit rate due to neutron Apply timing cut…

12. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy12 Efficiency Loss due to Blindness Catcher may be “blinded” due to other activities  Blinded modules become less efficient for photons –Photon efficiency loss found to be 1.1% (prompt  + neutrons) –Double pulse resolution is quite important !! (We used 3ns in the calculation above) Hit pattern of prompt beam  Overlay on  event Expected event map This cluster survives This cluster be killed

13. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy13 Proof of Principle 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) PT2 PT1

14. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy14 Summary (1) In-beam Photon Veto in KOPIO Beam Catcher System –Aerogel counter inside beam –Acrylic sandwich counter in halo region Expected performance meets our requirement –High efficiency for photons (>99% @ 300MeV) –Low fake hit probability due to neutrons (0.3% @ E kin =800MeV) –Signal loss due to false hit will be ~5% –Catcher efficiency loss due to blindness ~1%

15. May 26-27, 2005Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy15 Summary (2) Proof-of-Principle experiments have been done –two generations of prototype –MC is found reliable  We are ready for production !! Full size prototype now under construction