1. HLab meeting 5/22/07 K. Shirotori

2. SP0 Beam decay background veto SP0 :  - from K - →  - +  0 Background  - is vetoed by detecting  rays from the decay of co-decay product  0. Trigger rate: ~400 /0.7 sec spill

3. SP0 design A set of counters consisting of lead plates sandwiched by timing counters is used.   -ray energy: 70-1200 MeV Only  -ray detection not to measure the energy  As good efficiency as possible  As thin as possible : less than 16 cm ⇒ Can we use parts of Range counter used in E559 experiment (  + search) ? –To change the degrader material : Brass → Lead

4. Range counter 1200 1100 ・・・・・ 10 layers Scinti 8 mm Brass (disc) 3 mm Brass (plate) 6 mm Order (Scin Disc (Big→Small) Plate Scin) To remove disc, change brass to lead and adjust the hole size Beam

5. SP0 design 鉛 30 mm (3 mm×10 layers) 左右両側のシンチはそのまま 中心部のシンチは穴を狭める様に配置 中心部両側のシンチは削る 全厚 : 11(3+8)mm×10 layers + 8 mm シンチ = 118 mm <160 mm

6. SP0 design in simulation  全体のサイズは縮小 1400×1400 → 1200×1100  シンチ 8 mm + 鉛 3mm : 10 layers  穴のサイズは一律、 400×130 mm 2 に従うようにした ( 図では紫やオレン ジになっているが穴は開いている )  中央両側のシンチも一律同じように 削った ( アクセプタンス的には最適化 していない、損する方向 )  厚さは方向には 118 mm ある 1100 1200 400 130 170

7. Acceptance & Efficiency Acceptance : 86 % Efficiency : 80 % Hole 584 cm 2 Acceptance : 87 % Efficiency : 81 % Hole 520 cm 2 Acceptance : 84 % Acceptance is not greatly reduced by changing the size of SP0 because the multiplicity of  -ray is two and  rays are emitted to the forward direction.

8. Hit pattern Hit pattern of SP0 Normal Small If only the region 800×800 mm 2 is selected, the acceptance for decay  rays becomes ~80 %. →Outer region is not so important. The size of SP0 can be smaller than that of simulated one. →It is better to reduce the accidental kill.

9. Summary & Plan Modified Range counter can be used as SP0. –Efficiency ~80 % SP0 can be designed to be smaller size. –To optimize the size Estimation of the single rate –To estimate the accidental kill by background events (low energy  ray, neutron, e.t.c)