The Study of Muon-induced Neutrons in The KIMS Experi

ment

2005. 10. 22.The Korean Physical Society

J.H. Choi

2005-10-22 2

Underground Laboratory

Yangyang KIMS Lab.Depth : 700m 2000m(mwe)

2005-10-22 3

P.Lipari et al., Phys.Rev.D44(1991)3543

• The high energy muon can pas

s through an underground in de

pth.

• Neutrons can be generated by t

he muon when the muon throug

h out material – mimic WIMP

• The everage energy of muons i

s 216 GeV at 2500 mwe in IGE

X lab.

• The flux of cosmic muon is 2.7x

10-3 cnt/m-2s-1 at 2000 mwe in KI

MS lab.

Muon Spectrum in Laboratory

Geant4 Simulation

dN /

dE

Energy [MeV]

KIMS

2005-10-22 4

• CsI(Tl) crystal is shielded by 30c

m mineral oil, 15cm lead, 5cm PE,

10cm Cu

• All of other detectors are surround

ed by the muon detectors

• Neutron detector is located inside

PE and outside Cu

• CsI crystal detector is in the copp

er box.

Detector

2005-10-22 5

• We expected that we can find the

coincidence of neutron and muon

detector

• We computed the time difference

Δt between muon and neutron det

ector’s signal

• Δt = Min(Muon trigger time – Neutr

on trigger time)

• The pick shows the information of

coincidence

Time Coincidence

Δt [sec]

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• 2 candidates of muon-induced neutrons are found• The size of data is too small

Muon-induced Neutron

Energy [MeV]

0.025 cnt/day/liter

Events of neutron energy region

Coincident events of neutron energy region

Experiment Result

Ener

gy [M

ev]

PID [MeV/MeV]

Gamma Neutron

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Geant4 Simulation

• Total 282,000 muons are fired with angle distributions.

- 170.8 days(MC) / 67.4 days(Exp)

Energy [MeV]

Length [cm] Theta Angle [degree]

Phi Angle [degree]

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Generated Neutrons in Detector

• Most of neutrons are generated in the lead.- 2.45 x 10-10 cnt/cm-3s-1

Total

Lead Length [cm]

Length [cm] Energy [MeV]

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Generated Neutrons – 1cm and 35cmTotal Seconda

ryPrimary

84 %

22 %

16 %

78 %

• The rate of neutron production of Fluka is at most 2 times more than Geant4 over 100GeV.

• The rate of neutron production of Geant4 depend on physics model at least 2 times.

Energy [MeV]

Energy [MeV]Energy [MeV]

Energy [MeV]

Energy [MeV]

Energy [MeV]

1.46x10-4 /muon/(g/cm2)

By Geant4

IGEX : 8.8x10-5 /u/(g/cm2)By Fluka Simulation

4.6x10-4 /u/(g/cm2)

By Geant4

IGEX : 1.7x10-3 /u/(g/cm2)By Fluka Simulation

2005-10-22 10

Deposited Coincedence Energy - MC• The coincidence events rate wit

h muon detector is 38.94 evt/da

y under 150 MeV

• The coincidence events rate wit

h muon detector is 8.30 evt/day

over 2.5 MeV

• In the high energy, most of evne

ts are from muon

• In the low energy, most events a

re from E.M.

• Neutron is not detected in the 1

70.8 days MC simulation data

– We need more statistics

– We need study of MC model de

pendence

ToTal : 38.94 evt/day

Muon : 4.32 evt/day

E.M. : 34.62 evt/day

0 ~ 150MeV

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• The coincidence events rate w

ith muon detector is 14.64 evt/

day from 150KeV to 10 MeV

• The coincidence events rate w

ith muon detector is 5.21 evt/d

ay over 2.5 MeV

• In the 67.4 days data, two ca

ndidate events of muon-induc

ed neutrons are detected

Exp. : 5.21 evt/day

M.C. : 8.30 evt/day

2.5 MeV ~

Coincedence Energy – Exp.

2005-10-22 12

Coincidence Low Energy

150KeV~2.5MeVMC 16.31 evt/day

Exp. 9.36 evt/day

• The coincidence events rate w

ith muon detector is 16.31 evt/

day from 150KeV to 2.5 MeV i

n M.C.

• The coincidence events rate w

ith muon detector is 9.36 evt/d

ay from 150KeV to 2.5 MeV in

Exp.

2005-10-22 13

Summary & Plan• The flux of cosmic muon at 2000 mwe in KIMS lab is 2.7x10-7 cnt/cm-2s-1

• The rate of generated neutrons by Geant4 MC simulation is 2.45 x 10-10 cn

t/cm-3s-1 in lead of KIMS detector.

• The rate of generated neutrons in 35cm Pb

4.6x10-4 /muon/(g/cm2) (KIMS-Geant4) : 1.7x10-3 /muon/(g/cm2) (IGEX-Fluka)

• Total Coincidence events (150KeV~2.5MeV)

9.36 evt/day(Exp.) : 16.31 evt/day(M.C.)

• 2 candidates of muon-induced neutrons are found in KIMS Experiment

• We need more statistics for M.C.

• These result will be also tested with adequate physical model of Geant4

• We are studying the coincidence between the muon detector and the CsI

detector