Post on 21-Jan-2016
description
Status of KIMS
S.S. Myung (SNU)
For the KIMS Collaboration
• Results from 4 crystal array• Status of 12 crystal array
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.MyungSeoul National University
U.G.Kang, Y.D.Kim, J.I. LeeSejong University
H.J.Kim, J.H.So, S.C.Yang Kyungpook National University M.J.Hwang, Y.J.KwonYonsei University
I.S.Hahn Ewha Womans University
Y.H.Kim, K.B.Lee, M. Lee KRISS
J.LiInstitute of High Energy Physics D. He, X.Li, Q.YueTsinghua University
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.MyungSeoul National University
U.G.Kang, Y.D.Kim, J.I. LeeSejong University
H.J.Kim, J.H.So, S.C.Yang Kyungpook National University M.J.Hwang, Y.J.KwonYonsei University
I.S.Hahn Ewha Womans University
Y.H.Kim, K.B.Lee, M. Lee KRISS
J.LiInstitute of High Energy Physics D. He, X.Li, Q.YueTsinghua University
Mostly Dark matter, Dark energy
Composition of Universe
02.002.1 matter
Known ~ 4%
property of neutrinosnot known very well
Galactic Dark Matter
Density of dark matter around the sun ~ 0.3 GeV /cm3 ( ~ 5 x 10-28 kg/cm3)
rotation velocity curve
WIMP
Cs
IRecoiled nucleus
Direct detection of galactic dark matter
Recoil energy ~ 10’s keVEvent rate < 1/kg/day
Neutralinos the strongest WIMP candidate because they hardly interact and are stable
WIMP detection techniques
WW
N
Phonon(heat) Photon(light)
Ionization
+ _+ __+
Energy lost by recoiled nucleus converts to phonons, photons, ion pairs
HPGe detector
NaI(Tl), CsI(Tl), Xe
2 phase XeCryogenic detector
Ge, Si
KIMS
Yangyang Underground Laboratory(Y2L)Yangyang Underground Laboratory(Y2L)
3.5 hours by car
Yangyang Underground LaboratoryKorea Middleland Power Co.
Yangyang Pumped Storage Power Plant
~2 km
Vertical Depth ~700m
KIMS
OFHC Cu 10cm : 3t
Detector and Shielding
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
• 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
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 Resolution @ 59.5 keV : 7.3%
Internal background
Radioisotopes in the crystal
137Cs : 10 mBq/kg,
0.35 cpd/mBq/kg @ 10 keV
134Cs : 20 mBq/kg
0.07 cpd/mBq
0.005 cpd/mBq87Rb : 10 ppb
1.07 cpd/ppb
Geant Geant SimulationSimulation
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
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 )
Other Detector Components
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
Neutron calibration
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
NeutroNeutronnsamplesample
GammaGammaFull Full sizesize
GammaGammasamplesample
Tag γ(4.4MeV)to measure TOF and energy of neutrons
Note: their shapes areWell matching
<t>=( Ai ti)/ Ai
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 8.7 1030
B0510A 5.9 8.7 616
B0510B 5.9 8.7 616
Total 34.8 3409
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), 840 kg days(0510B)PMT only ~350 kg days for each crystal with the PMTS used for each crystal
Data analysis for Wimp Search
clear boxPMT PMT
Reduction of PMT noise
GammaNeutronPMT only(dot-dashed)WIMP search DATA
PMT noise
Decay timelog(τf)
LL2-LL1
fit result for one event
Analysis Method: Event selection
remove multi-crystal events
0.7 cpd bkg reduction
Gamma PMT background WIMP search DATA
Asymmetry Cut3-5 keV
5-7 keV
Efficiency
NeutronCompton events
S0501AS0501BB0510AB0510B
Efficiency CorrectedEfficiency Corrected
WIMP search data with cutWIMP search data with cut
Event rates after cuts
Modeling of Calibration data with asymmetric gaussian function
NR event rate estimation
• Fit the WIMP search DATA with PDF function from gamma and neutron calibration data
extract NR events rate
n
Electron recoilNuclear recoilBest fit
Extracted NR
S0501AS0501BB0510AB0510B
NR Event rates
90% CL limit
Geant4 expectation
Total Rate:
Extracted NR is fitted with simulated WIMP signal for each WIMP mass
Nuclear recoil of 127Iof DAMA signal region
is ruled out unambiguiously
Nuclear recoil of 127Iof DAMA signal region
is ruled out unambiguiously
ρD=0.3 GeV/c2/cm3
v0=220km/s, vesc=650km/s
Systematic uncertainty ~15%
Cross-section upper limits
PRL 99, 091301 (2007)
Spin-Independent SD, Wimp-Proton
Name Weight (kg)
Data(kg
days)
S0406 6.7 237
S0501A 8.7 1147
S0501B 8.7 1030
B0510A 8.7 616
B0510B 8.7 616
B0511 8.7
B0601 8.7
B0605A 8.7
B0605B 8.7
B0606A 8.7
B0606B 8.7
B0609 8.7
B0609 8.7
published PLB(2006)
background level2~4 cpd/keV/kg (preliminary)
Total crystals 8.7 kg x 12 = 104.4 kg
started data taking
Pilot run
Engineering run
published PRL(2007)
12 crystal array
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.
(sec)
High Energy muon event in CsI detector
5us
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.
keV(electron recoil equivalent E)
cpd
20days data
Multi hit event is rejected.
8ms dead time after high energy event is applied by hardware setting.
Event rate of muon tail event for det0
Muon Coincidence signal
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
• Result using 3409 kg days data PRL 99, 091301 (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
Summary and Prospects
rEE
R
RerE
R
dE
dR0/
0
0
)χ~
χ~
( 01
01 NN
Elastic Sacttering of WIMP off a nuclues in the detector
10-6 ~ 10-10 pb
Expected event rate ~ 1/kg/day or less
WIMP signal
R : event rateR0: total event rateE0: most probable incident kinematic energyr : kinematic factor, 4MwMN/(MW+MN)2
Recoil energy < 100 keVMeasured energy < 10 keV due to quenching Very
small
Very small
Very small
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
Effect of cuts on MT distribution
Data Gamma
Neutron PMT
Base cutFit qualityAsymtail
Background level
PMT noise cut applied
Muon tail events rejected
Cut efficiency not corrected
cpd
keV
preliminary
Previous run
• WIMP Nucleus Scattering
• Spin Independent
• Spin Dependent
ρρχχ=galatic halo density =galatic halo density vvEE=earth velocity in galatic =earth velocity in galatic frameframevv00=sun velocity in galatic frame=sun velocity in galatic frame
Cross Section
WIMP Nucleus Cross section
Scalar: Spin independent interaction
-> coherent amplification via constituent nucleon Axial: Spin dependent interaction
-> coupling depends on proton & neutron spin expectation value
WA
Latest WIMP search analysis results
Isotope J Abun <Sp> <Sn>133Cs 7/2 100% -0.370 0.003127I 5/2 100% 0.309 0.07573Ge 9/2 7.8% 0.03 0.38129Xe 1/2 26% 0.028 0.359131Xe 3/2 21% -0.009 -0.22719F 1/2 100% 0.441 -0.109