1. K0 beam line for the E391a experiment
May 27, 2005
Takao Inagaki (KEK)

2. Location

4. Collimation scheme

5. KL spectrum and n andγprofiles

6. Telescope for the profile measurement

7. Profiles　(meas. vs MC*)

8. Sizable vacuum effect

9. Detectors for energy spectra
SLSD (+ lead glass)
Cerberus

10. γspectra measured by SLSD+lead glass

11. Neutron and γ spectra by Cerberus

12. C4: suppressor of thermal neutron flux

13. Profiles and spectra of the halo
Measured by Cerberus

14. Decay vertex distribution for 2γsample at trigger bias

15. How are the halo neutrons generated?
Scattering at C2 +
Hadronic Shower at C6
Main source of
lower-energy tail events
~ 25 % events
Multiple Scattering
Main source of
higher-energy edge events

16. Summary
The profiles and spectra including the absorber effects were rather well reproduced by a MC simulation using GEANT(G-FULKA) code.
Beam-line design becomes science from art.
Further improvement:
・　suppress the second step scattering
　 ・　decrease n/KL ratio

17. Supplement

19. How are the halo neutrons generated?
It consists of two kinds of source.
From first look of e391 data, we have to reduce halo!!!

20. How are the halo neutrons generated?
Multiple Scattering,
1st scattering is in the Pb absorber.
No. of event is rather large.
~ 20 % of halo events
Scattering at Vacuum window.

21. Summary for halo-neutrons
Source of halo neutrons:
1. Multiple scattering
typical case
(a) C2C6halo
(b) Pb abs  C6  halo (20%)
2. Hadronic shower at C6 (ex, C2C6shower) ( 25 %)
Possible way:
1. Position of trimming collimator relative to Pb abs.
2. Active veto-counter at C6.
Test of New Collimation Scheme…