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

Task Kpnn experiment needs hermetic veto system Signature = 2g + nothing Veto detectors surrounding Decay Region Particles can escape through the beam hole 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 May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

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

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy Solution Utilize Cherenkov radiation Aerogel tile (n=1.05) or Acrylic slab radiator Avoid detection of slow particles from neutron interactions Slow p, 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 g from secondary p0 (neutron interaction and KL decay in the detector) May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

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

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 May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

KOPIO Catcher System In-beam Aerogel Catcher Halo Guard counter 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 X0 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 May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

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

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

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

Signal Loss due to Catcher False Hit Accidental hit due to neutrons may kill Kpnn signal Neutron rate False hit (rate x hit prob.) False hit rate due to neutron Total false hit probability was found ~ 0.4 events / m-bunch Integrated over the duration consistent with the arrival time of g from our signal KL 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 Apply timing cut… May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

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 g + neutrons) Double pulse resolution is quite important !! (We used 3ns in the calculation above) Hit pattern of prompt beam g Overlay on g event Expected event map This cluster survives This cluster be killed May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy Proof of Principle PT2 PT1 Prototype 1 (2001-2) 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) May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy 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% @ Ekin=800MeV) Signal loss due to false hit will be ~5% Catcher efficiency loss due to blindness ~1% May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

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 May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy