1. For the KIMS Collaboration
Status of KIMS
S.S. Myung (SNU)
For the KIMS Collaboration
Results from 4 crystal array
Status of 12 crystal array

2. KIMS Collaboration
H.C.Bhang, J.H.Choi, D.W.Kim, S.C.Kim, S.K.Kim, J.H.Lee,H .S.Lee, S.E.Lee, J. Lee, S.S.Myung
Seoul National University
U.G.Kang, Y.D.Kim, J.I. Lee
Sejong University
H.J.Kim, J.H.So, S.C.Yang
Kyungpook National University
M.J.Hwang, Y.J.Kwon
Yonsei University
I.S.Hahn
Ewha Womans University
Y.H.Kim, K.B.Lee, M. Lee
KRISS
J.Li
Institute of High Energy Physics
D. He, X.Li, Q.Yue
Tsinghua University

3. Mostly Dark matter, Dark energy
Composition of Universe
Mostly Dark matter, Dark energy
Known ~ 4%
property of neutrinos
not known very well 3

4. rotation velocity curve Direct detection of galactic dark matter
WIMP Cs I
Recoiled nucleus
Recoil energy ~ 10’s keV
Event rate < 1/kg/day
Neutralinos the strongest WIMP candidate because they hardly interact and are stable
Density of dark matter around the sun
~ 0.3 GeV /cm3 ( ~ 5 x kg/cm3) 4

5. WIMP detection techniques
Energy lost by recoiled nucleus converts to phonons, photons, ion pairs
KIMS
Phonon(heat)
Photon(light)
NaI(Tl), CsI(Tl), Xe W W
Cryogenic
detector
Ge, Si + _ + _ + _
2 phase Xe N
Ionization
HPGe detector

6. Yangyang Underground Laboratory(Y2L)
3.5 hours by car

7. Yangyang Underground Laboratory
Korea Middleland Power Co.
Yangyang Pumped Storage Power Plant
Vertical Depth ~700m
~2 km
KIMS

8. Detector and Shielding
OFHC Cu 10cm : 3t

9. Why CsI(Tl)? Sensitive to both SD and SI WIMP interactions
Ge, Xe not sensitive to SD proton coupling
 complimentary to CDMS, XENON-10
 direct check of DAMA signal by I-127 recoil
Easy to get large mass with an affordable cost
 annual modulation study
High light yield ~60,000/MeV
Pulse shape discrimination
 better gamma rejection than NaI(Tl)
Easy fabrication and handling

10. Detector CsI(Tl) Crystal 8x8x30 cm3 (8.7 kg)
3” PMT (9269QA) : Quartz window, RbCs photo cathode (Green enhanced)
~5 Photo-electron/keV
Total charge spectrum for 59.5 keV Am241
keV : 7.3%

11. Internal background Radioisotopes in the crystal
137Cs : 10 mBq/kg,
keV
134Cs : 20 mBq/kg
0.07 cpd/mBq
0.005 cpd/mBq
87Rb : 10 ppb
1.07 cpd/ppb
Geant Simulation
Cs-137 reduction – use ultra pure water in powder prodcution; ~1.7 mBq/kg
Rb reduction - recrystalization method ; < 1ppb
Latest crystals are from ~2 cpd level powder 11

12. Other Detector Components
Muon Detector
4 coverage muon detector : 28 channels
Liquid Scintillator(5%) + Mineral Oil (95%) = 7 ton
Measured Muon flux = 2.7 x 10 –7 /cm2/s
Position resolution : σx, ~ 8 cm
Reconstructed muon tracks with hit information
Muon veto efficiency ~99.9%
Neutron detector
1 ~ 1.2 liter BC501A liquid scintillator x 3
n/gamma separation using PSD
E_vis > 300 keV
Measured neutron flux (outside shield)
 8 x 10 –7 /cm2/s ( 1.5 < E neutron < 6 MeV ) 12

13. Study of Muon induced neutrons
Coincidence between Muon and Neutron detectors
n/gamma separation using PSD
Neutron energy: 0.4MeV<E<2.75MeV
Measured : (3.8±0.7)10-2 counts/day/liter
GEANT4 : (2.0±0.2) 10-2 counts/day/liter

14. Neutron calibration 300 mCi Am/Be source
Tag γ(4.4MeV)
to measure TOF and
energy of neutrons
300 mCi Am/Be source
 neutron rate 7 x 105 neutrons /sec
 a few 100 neutrons/sec hit
3cm  3cm  3cm crystal ( sample )
 Quenching factor of Recoil Energy
NR mean time distribution
Neutron
sample
Gamma
Full size
<t>=(S Ai ti)/S Ai
Note: their shapes are
Well matching 14

15. Data analysis for Wimp Search
Data used for this analysis
Crystal
p.e./keV
Mass(kg)
Data(kg·days)
S0501A
4.6
8.7
1147
S0501B
4.5
1030
B0510A
5.9
616
B0510B
Total
34.8
3409

16. Data analysis for Wimp Search
Calibration and control data samples
Neutron ~ 500 kg days (at 4~6 keV)
Gamma (using 137Cs) ~ 1100 kg days (0501A), 1650 kg days(0501B)
910 kg days (0510A), kg days(0510B)
PMT only ~350 kg days for each crystal with the PMTS used
for each crystal
clear box
PMT 16

17. Reduction of PMT noise PMT noise log(τf) fit result for one event
Decay time
fit result for one event
LL2-LL1
Gamma
Neutron
PMT only(dot-dashed)
WIMP search DATA

18. Analysis Method: Event selection
remove multi-crystal events
0.7 cpd bkg reduction
3-5 keV
Asymmetry Cut
Gamma
PMT background
WIMP search DATA
5-7 keV

19. Efficiency
Compton events
Neutron 19

20. WIMP search data with cut
Event rates after cuts
WIMP search data with cut
S0501A
S0501B
B0510A
B0510B
Efficiency Corrected

21. NR event rate estimation
Modeling of Calibration data with asymmetric gaussian function n g
Electron recoil
Nuclear recoil
Best fit
Fit the WIMP search DATA with PDF function from gamma and neutron calibration data
 extract NR events rate 21

22. NR Event rates
Extracted NR
S0501A
S0501B
B0510A
B0510B 22

23. Geant4 expectation
90% CL limit
Total Rate:
Extracted NR is fitted with simulated WIMP signal for each WIMP mass

24. is ruled out unambiguiously
Cross-section upper limits
Spin-Independent
SD, Wimp-Proton
PRL 99, (2007)
ρD=0.3 GeV/c2/cm3
v0=220km/s, vesc=650km/s
Systematic uncertainty ~15%
Nuclear recoil of 127I
of DAMA signal region
is ruled out unambiguiously 24

25. 2~4 cpd/keV/kg (preliminary)
12 crystal array
Name
Weight (kg)
Data
(kg days)
S0406
6.7
237
S0501A
8.7
1147
S0501B
1030
B0510A
616
B0510B
B0511
B0601
B0605A
B0605B
B0606A
B0606B
B0609
published
PLB(2006)
Pilot run
published PRL(2007)
Engineering run
Total crystals
8.7 kg x 12 = kg
started data taking
background level
2~4 cpd/keV/kg (preliminary)

26. Study of Muon Coincidence signal
Muon coincidence event rate: ~6evt/hr for 12 detectors
Muon coincidence event is very high energy event and
triggers multi-crystals.
It requires a few tens of ms for scintillation to disappear.
High Energy muon event in CsI detector
5us
(sec)

27. Muon Coincidence signal
Event rate of muon tail event
-> muon tail event is defined as the event which shows up within
30ms from the start of Muon coincidence event.
Event rate of muon tail event for det0
20days data
Multi hit event is rejected.
8ms dead time after high energy event is applied by hardware setting.
cpd
keV(electron recoil equivalent E)

28. Short remarks on Annual Modulation Study in KIMS
Have been taking data with 100 kg array for ~7 months
AM study without applying PSD can be done
With 100kg CsI(Tl), ~3 cpd background level
if no AM:
one-year-run -> upper limit on AM amplitude
< 0.01 cpd/keV/kg level with 90% CL
if AM amplitude ~ 0.02 cpd/keV/kg
two years data is required to confirm
with more than 3σ significance 28

29. Summary and Prospects Result using 3409 kg days data
PRL 99, (2007)
DAMA signal region is ruled out for both SD and SI interactions
at WIMP mass > 20 GeV
Most stringent limit on SD interactions for pure proton case
Successfully reduced internal backgrounds of CsI(Tl) crystals (latest powder ~ 2cpd)
12 full size crystals(8x8x30cm3) ~ 100 kg
Current shielding can accomodate 250 kg
100 kg crystals installed in the shield and data taking was started
 Annual modulation search 29

32. Elastic Sacttering of WIMP off a nuclues in the detector
WIMP signal
Elastic Sacttering of WIMP off a nuclues in the detector
Very
small
10-6 ~ pb
Expected event rate
~ 1/kg/day or less
Very
small
Recoil energy < 100 keV
Measured energy < 10 keV
due to quenching
R : event rate
R0: total event rate
E0: most probable incident kinematic energy
r : kinematic factor, 4MwMN/(MW+MN)2
Very
small

33. Analysis Method: Event selection
Multi hit event rejection
Fit quality cut
fitted τf
log likelihood value for two exponential fit and one exponential fit
ratio of fitted mean time to the calculated mean time
Short component rejection
ratio of tail (t> 10 μs) to the whole amplitude
Asymmetry cut

34. Effect of cuts on MT distribution
Data
Gamma
Base cut
Fit quality
Asym
tail
PMT
Neutron 34

36. Background level Previous run cpd preliminary keV
PMT noise cut applied
Muon tail events rejected
Cut efficiency not corrected
keV 36

37. Cross Section WIMP Nucleus Scattering Spin Independent Spin Dependent
ρχ=galatic halo density
vE=earth velocity in galatic frame
v0=sun velocity in galatic frame
Spin Independent
Spin Dependent 37

38. WIMP Nucleus Cross section
Latest WIMP search analysis results
WIMP Nucleus Cross section
Isotope J
Abun
<Sp>
<Sn>
133Cs
7/2
100%
-0.370
0.003
127I
5/2
0.309
0.075
73Ge
9/2
7.8%
0.03
0.38
129Xe
1/2
26%
0.028
0.359
131Xe
3/2
21%
-0.009
-0.227
19F
0.441
-0.109
Scalar: Spin independent interaction
-> coherent amplification via constituent nucleon
Axial: Spin dependent interaction
-> coupling depends on proton & neutron spin expectation value