Underground Experiments in Korea
Sun Kee Kim
Seoul National University
ASK 2011
April 11-12, 2011, Seoul
Questions on our Universe
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What is the Universe made of?
How big is the Universe?
How did the Universe begin?
What is the destiny of the Universe?
What is the meaning of life in the Universe?
…
Some of these questions may be answered
by understanding the nature of Dark matter
and Neutrinos
“The most incomprehensible thing about the world is that it is comprehensible”
- A. Einstein -
Standard Model of Elementary Particles
Quarks and leptons : Spin 1/2
e,  , , e ,  , 
u, d , s, c, b, t
properties are not understood very well
Gauge Bosons
Spin 1:, W  , Z , g
Spin 2 : G
Higgs Bosons : Spin 0
H , h0 , h , A
expected to be discovered at LHC
Great achievement with partcile accelerators during the last century !
Composition of our Universe
  matter    1.005  0.006
Mostly Dark …
Dark Energy
73%
Dark Matter
23%
Matter made of
known
particles
4%
Existence of dark matter by astronomical observations
In 1933, Zwicky observed that the rotational
speed of galaxies in a cluster of galaxies (Coma
cluster) too fast to be explained by mass of
galaxies in the cluster
Gravitational lensing by cluster of galaxies
Collision of galaxy clusters
Rotation curves of galaxies
Cosmic Microwave Backgroun
Density of dark matter around the sun ~ 0.3 GeV /cm3
~ 5 x 10-28 kg/cm3
First idea of WIMP in 1977
by B.W.Lee and S. Weinberg
WIMP
(Weakly Interacting Massive Particles)
Relic abundance
h
27
3 1
3

10
cm
s
2
 h 
 Av
H
~ 0.7,  A : annhilatio n cross section,  : realtive velocity
100km / s / Mpc
Annihilation cross section of a particle with a weak scale
interaction
 Av ~  2 (100GeV)2 ~ 1025 cm3s 1
 Excellent CDM candidate
LSP in SUSY
Elastic scattering of SUSY WIMP with ordinary nucleus
Spin Dependent Interaction
Laxial  d q    5q    5q
32
 spin  GF 2  2  2 J ( J  1)

1
  (a p  S p   an  Sn )
J
Spin Independent Interaction
Lscalar  aq  q q
 scalar 
4

 2  Zf p  ( A  Z ) f n 
 A2
XLIIInd Rencontres de MORIOND
8
2
Direct Search for WIMP
Elastic Sacttering of WIMP off a nuclues in the detector
~0
~0
 (χ 1 N  χ 1 N )
WIMP
Recoiled nucleus
R0  ER / E0 r
dR

e
dE R E0 r
R : event rate
R0: total event rate
E0: most probable incident kinematic energy
r : kinematic factor, 4MwMN/(MW+MN)2
• Recoil energy < 100 keV
• Expected event rate
<1/kg/day or less
Status of WIMP search
DAMA Annual Modulation
=60o
vsun=232km/s
sun
2-6 keV
vorbit=30km/s
earth
Fit :Acos[w(t-t0)]
A=(0.0129±0.0016) cpd/kg/keV
2/dof = 54.3/66 8.2  C.L.
Neutrino mass and mixing
measurable by neutrino oscillation
needs to be measured
DayaBay, DCHOOZ, RENO
needs to be measured
Neutrinoless Double Beta Decay
Energy
100Tc
100Mo
Q
Forbidden b
transition
Transition bb
allowed
bb
100Ru
Z
Z
0νββ decay occurs
when mν≠0 and ν = ν
Z+1
Z+2
T1/ 2 0bb  ~  mbb  2 M 0
2
Status of DBD searches
Positive signature?
100 meV
25 meV
2meV
need 1 ton detector
Challenges for Rare Processes
Dark Matter (Direct detection of WIMP)
- Very weak interactions with ordinary matter : Rare
- Very low energy signals
- Large background
- Nuclear recoil vs electron recoils
Neutrinoless Double Beta Decay Search
- Life time is expected to be very long : Rare
- Large background
- 2νββ vs 0νββ Self background
These searches cannot be performed
without an Underground Laboratory
without an excellent detector performance
Why underground Laboratory ?
Cosmic ray 106eV ~ 1020eV, p, He,…
Nuclear interaction - secondary particles
1 muon /second/10 cm x 10 cm at sea level
Muon interaction creates neutrons
Neutron
- mimic WIMP signal
- generate radioactive isotopes
Neutrons from rocks can be avoided by a proper shielding
But, if muons interact within the shield, neutrons can enter the detector
Need to reduce the muon flux as much as possible
Deep underground experimental site
Underground Laboratories
Boulby
Mine
NAIAD
ZEPLIN
DRIFT
Sudbury
PICASSO
Soudan Mine
CDMS
COUPP
Canfrane
ANAIS
IGEX
Frejus
EDELWEISS
Super NEMO
Gran Sasso
DAMA, LIBRA
XENON,
CRESST
CUORE, GERDA
Suchiwan
ULGe
Xenon
Kamioka
Yangyang
KIMS
AMORE
XMASS
Yangyang Underground Laboratory(Y2L)
Yangyang Underground Laboratory
(Upper Dam)
Korea Middleland Power Co.
Yangyang Pumped Storage Power Plant
(Power Plant)
(Lower Dam)
Construction of Lab. buildings done in 2003
Minimum depth : 700 m / Access to the lab by car (~2km)
KIMS(Korea Invisible Mass Search) collaboration
H.C.Bhang, J.H.Choi, S.C.Kim, S.K.Kim
J.H.Lee, M.J.Lee, S.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
Korea Research Institute of Standard
Sciences
J.Li
Institute of High Energy Physics
Y.Li, Q.Yue
Tsinghua University
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KIMS research program
Dark Matter Search
- CsI(Tl) crystal detector
An intermediate result was published (2007)
100 kg array running
Neutrinoless Double Beta Decay Search
- Metal loaded liquid scintillator
- HPGe detector + CsI(Tl) crystal + Sn, Zn,..
to excited states, beta+ decays
- CaMoO4 crystal
- scintillation technique
- cryogenic technique
WIMP search with CsI(Tl) Crystals
Easy to get large mass with an affordable cost
 Good for AM study
High light yield ~60,000/MeV
Pulse shape discrimination
 Moderate background rejection
Easy fabrication and handling
Cs-133, I-127 (SI cross section ~ A2)
Both Cs-133, I-127 are sensitive to SD interaction
electron recoil
nuclear recoil
Isotope
J
Abun
<Sp>
<Sn>
133Cs
7/2
100%
-0.370
0.003
127I
5/2
100%
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
KIMS(Korea Invisible Mass Search)
DM search experiment with CsI crystal
CsI(Tl) Crystal 8x8x30 cm3 (8.7 kg)
3” PMT (9269QA) : Quartz window, RbCs photo cathode
~5 Photo-electron/keV
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WIMP search limit with 4 crystals
PRL 99, 091301 (2007)
Nuclear recoil of 127I of DAMA signal
region is ruled out unambiguiously
Most stringent limit on SD(pure proton)
interactions
Data taking with 12 crystals
12 crystals(104.4kg) running (from 2008)
• Stable data taking for more than a year
• Unique experiment to test DAMA annual
modulation
CsI DAQ rate < 6 Hz
Total exposure: 32793 kg days
Sep. 2009 ~ Aug. 2010
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Am-241 Energy Calibration
Am calibration
-> ~5 p.e /keV
13.9keV Np L X-ray
17.8keV Np Lb X-ray
20.8keV Np L X-ray
26.35keV gamma
Cs, I
X –ray escape
59.54
gamma
Relative
intensity.....
E(keV)
25
High energy tail events rejection
5us
Additional cut: Muon veto, file up rejection, trigger
condition
cut, multiple hit rejection
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NR event rate estimation

n

Modeling of Calibration data with
asymmetric gaussian function
Electron recoil
Nuclear recoil
Best fit
• Fit the WIMP search DATA
with PDF function from
gamma and neutron
calibration data
 extract NR events rate
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Surface alpha (SA) events background
222Rn
progenies produce this background.
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Study of SA events
with Rn progeny contaminated crystal
Sides are wrapped by teflon
A
CsI(Tl) crystals
A: Rn progeny contaminated
-exposed to Rn gas
for one week
B
B: clean
Background
Surface alpha events
Aluminum foil
t=2um x 3 layers
mean time(mt)
Tagged as
Alpha at part B
E(keV)
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The logrmt10 distribution for various types of particle
PSD parameter
neutron
SA
gammas
rmt10   t  pulse (t )dt /  pulse
(t )dt
30
in 10s
Modeling WIMP search data with 3 components, SA, NR, gamma
3keV
4keV
det0
5keV
7keV
9keV
6keV
SA
NR(WIMP)
gamma
8keV
10keV
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Determination of the 90 % C.L. limit of NR event rates
Pdf = f0 x FNR + f1 x FSA + (1-f0-f1) x Fgamma
The posterior pdf of f0 & f1 are obtained
from Bayesian analysis method.
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NR events rate for det0 to
det12
Counts/day/kg/keV
Determined from
Bayesian method
-90% limit
-68% interval
3-11 keV
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KIMS WIMP search
Spin Independent
Spin Dependent
Plan on Annual Modulation Stuudy
Taking data for more than 18 months  2 year data by this summer
Sep. 2009 ~ Feb. 2011
~ 3 counts/day/kg/keV
DBD Searches at KIMS
 Passive targets : HPGe + CsI(Tl)
[Nuclear Physics A 793 (2007)]



64Zn
EC+b+ decay
124Sn bb to excited states of
122Sn EC+b+ decay
124Te
 Active targets

124Sn
0νbb : Sn loaded Liquid scintillator
[Astropart. Phys. 31,412 (2009)]
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
84Sr
EC+b+ decay : SrCl2 crystal
92Mo EC+b+ decay : CanatMoO crystal
4
100Mo 0νbb decay : Ca100MoO crystal
4
R&D effort is on going  birth of AMORE
β+EC decay of
92Mo
511keV γ
Gamma detector
Active crystal
with 92Mo
511keV γ
Conceptual setup
EC / b 
• 92Mo nucleus is double EC and beta plus EC
isotope
•EC/β+ Q-value=627keV, ECEC = 1,650keV
•Abundance = 92Mo: 14.84%, 100Mo: 9.63%
•e+ stops in active(CaMoO4) Crystal.
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β+EC decay of
92Mo
• PMTs & CsI crystals are crossly connected.
• Lead shielding(10 cm)
• CaMoO4 is surrounded by 14 CsI crystals
•U - CsI(Tl) crystals
•Th - CsI(Tl) crystals
•K – 1inch PMT
•K – CsI(Tl) crystals
•K – CaMoO4 crystal
T1/2 > 2.3 x 1020y (90% CL)
Paper in preparation
38
New HPGe detector at Y2L
Will be used for
- Measurement of internal background
- DBD search with beta+
~527 cc
~2.8kg
Co60/Cs137/Ba133
Energy
Resolution
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CaMoO4 for ββ
CaMoO4
 DBD for Mo-100 (3034 keV), Ca-48(4272 keV)
high energy  less background
 Mo-100 enrichment >90% not so difficult
 for Mo-100 search, Ca-48 need to be depleted
 Scintillator at room temp; 10-20% of CsI(Tl) at 20o
increases at lower temp.
 Decay time ; 16 μ sec
 Wavelength; 450-650ns-> RbCs PMT or APD
 Can be used as cryogenic detector (absorber)
Energy
100Tc
100Mo
Qbb
100Ru
Z
Z
Z+1 Z+2
CaMoO4 + LAAPD at -159oC
Compton edge
resolution
40Ca100MoO
4
Ca-48 Depletion needed
First
Mo-100 2β
Ca-48 2nββ
Signal (m=0.4eV)
Bi-214
Tl-208
SB28
CMO-3
S35
D44
mmxL51mm~300g
40Ca100MoO
4
crystal
after big bang
Cryogenic Detector
Advantages of using cryogenic calorimeters
High energy resolution (ΔE/E < 1/1000)
Ultra low energy threshold ( < 1 eV)
Simultaneous readout of Charge or Light
 discrimination of particle type (e, alpha, nuclear recoils)
e-h pair production : 3.6 eV in Si, 2.9 eV in Ge ( *kT (T=0.1K)~10 μeV)
(BG 1.11 eV in Si, 0.67eV in Ge) 2/3 energy goes to phonons…
For nuclear recoil ~10% goes to ionization
1 keV energy deposit : ~ 60 photons (CsI(Tl)) , ~280 e-h pairs (Si)
Cryogenic Detector
Energy absorption  Heat (Temperature)
, b, , etc.
Thermometer
Thermal link
Absorber
Heat sink < 100 mK
Choice of thermometers
• Thermistors (doped Ge, Si)
• TES (Transition Edge Sensor)
• MMC (Metallic Magnetic Calorimeter )
• STJ, KID etc.
Example
Metallic Magnetic Calorimeter
(MMC)
Field coil
junctions
g = 6.8
Magnetic material (Au:Er) in dc SQUID
Au:Er(10~1000ppm)
paramagnetic system
metallic host: fast thermalization ( ~ 1ms)
Can control heat capacity by magnetic field
5 mT  Δε = 1.5 eV
1 keV  109 spin flips
U. of Heidelberg
Experimental setup at KRISS with MMC
~ 500 m thick brass
crystal size
~ 1 cm  0.7 cm  0.6 cm
base temperature : 13 ~ 100 mK
45
45
Performance of CMO+MMC
Astroparticle Physics, 2011
5.5 MeV alpha FWHM = 11.2 keV
high energy resolution
suitable to search for Mo-100
0νββ
Emission line of Mo : 18keV
42 keV
60keV gamma
low energy threshold
suitable to search for WIMP
46
FWHM = 1.7 keV
CaMoO4 DBD Sensitivity
Scintillation technique
5% FWHM resolution
Cryogenic detector
0.5% FWHM 15 keV
FWHM
5 years, 100 kg 40Ca100MoO4
7.0x1026 years -> 20 – 70 meV
Dark matter sensitivity of CaMoO4 cryogenic experiment
CaMoO4
CDMS 2008
SuperCDMS 25kg
Eth=10 keV
(5 and 100 kg year)
XENON10 2007
Bottino et al
XENON100 6000 kgd
CMSSM, Ellis et al
CMSSM, Markov chain
Trotta et al
Effective MSSM,
Bottino et al
Eth=1 keV
(5 and 100 kg year)
Trotta et al
Ellis et al
AMoRE Collaboration
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

Korea (39)
Seoul National University : H.Bhang, S.Choi, M.J.Kim, S.K.Kim, M.J.Lee, S.S.Myung, S.Olsen, Y. Sato,
K.Tanida, S.C.Kim, J.Choi, S.J.Lee, J.H.Lee, J.K.Lee, H.Kang, H.K.Kang, Y.Oh, S.J.Kim, E.H.Kim,
K.Tshoo, D.K.Kim, X.Li, J.Li, H.S.Lee (24)
4 countries
Sejong University : Y.D.Kim, E.-J.Jeon, K. Ma, J.I.Lee, W.Kang, J.Hwa (5)
8 institutions
Kyungpook national University : H.J.Kim, J.So, Gul Rooh, Y.S.Hwang(4)
69 collaborators
KRISS : Y.H.Kim, M.K.Lee, H.S.Park, J.H.Kim, J.M.Lee, K.B.Lee (6)
Russia (16)
ITEP(Institute for Theoretical and Experimental Physics) : V.Kornoukhov, P. Ploz, N.Khanbekov (3)
Baksan National Observatory : A.Ganggapshev, A.Gezhaev, V.Gurentsov, V.Kuzminov, V.Kazalov,
O.Mineev, S.Panasenko, S.Ratkevich, A.Verensnikova, S.Yakimenko, N.Yershov, K.Efendiev, Y.Gabriljuk
(13)
Ukraine(11)
INR(Institute for Nuclear Research) : F.Danevich, V.Tretyak, V.Kobychev, A.Nikolaiko, D.Poda, R.Boiko,
R.Podviianiuk, S.Nagorny, O.Polischuk, V.Kudovbenko, D.Chernyak(11)
China(3)
Tsinghua University : J.Li, Y.Li, Q.Yue(3)
49
국가대형연구시설구축지도(National Facility Road Map (NFRM))
21개 S군에 선정됨 (NFRM에는 282 제안 중 69 선정, 69개는 다시 S,A,B군으로 분류)
SUMMARY
 KIMS :Results using 3409 kg days data (PRL 99, 091301 (2007))
 100 kg crystals installed in the shield and data taking is on going
 PSD result shown today
 Annual modulation study in progress
 DBD searches in various isotopes : Zn-64, Sn-124, Sn-122, Mo-92, Sr-84
 Some best limits
 Competitive DBD search using CaMoO4 crystals can be realized rather
soon  A new collaboration AMORE was formed
51
Thank you
Channeling


Well known technology to bend particle beam with crystal.
Studied a lot in 1960s
 Quenching is expected to be less


PSD may not work?
Less studied for low energy ions.
 Practically lower the trehsold
Na recoil
I recoil
Orange: w/o channeling
Green: w/ channeling
Savage, Gelmini, Gondolo and Freese, arXiv 0808.3607
When channeling is accounted, I recoil is preferred  better chance for KIMS
But, because of Blocking, the effect of channeling might be smaller than DAMA Claimed
Channeling
Understanding Quenching factorbetter is important.
Plan to measure quenching factor and channeling effect using a neutron setup
Also simulation study is on going together
CsI(Tl) Q.F
NaI(Tl) Q.F