recent progress of direct dark matter detection
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Recent progress of direct dark matter detection. S. Moriyama Institute for Cosmic Ray Research, University of Tokyo Oct. 8 th , 2011 @ FPUA2011, Okayama, Japan. Principle of direct detection in Lab. Dark matter hit detectors in Lab. Why interaction expected? - PowerPoint PPT PresentationTRANSCRIPT
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Recent progress of direct dark matter detectionS. Moriyama Institute for Cosmic Ray Research, University of TokyoOct. 8th, 2011 @ FPUA2011, Okayama, Japan
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Principle of direct detection in Lab.• Dark matter hit detectors in Lab. Why interaction expected?• Assume DM particles were thermally generated.• They annihilated into ordinary matter. This implies an interaction
between dark matter and ordinary matter (atoms). • Weakly Interacting Massive Particles (WIMPs)
Dark matter
Dark matter
Ordinary matter
Ordinary matterAnnihilation
Scatt
erin
g
1/temperature ~ time
Com
ovin
g nu
mbe
r den
sity
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How much dark matter around us?• It can be estimated by measuring rotational curve of
the galaxy. Local density ~ 0.3GeV/cc ~average x 105
• Isothermal, Maxwell distribution (<v> ~230km/s, <b>~10-3).R.P.Olling and M.R.Merrifield MNRAS 311, 369- (2000)
BuldgeSteller disk
Dark Halo
• These dark matter particles are expected to cause nuclear recoils even in underground lab.
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Signals after nuclear recoils• Small energy depositions (mp <v>2/2 < 1keV), rare.• Scintillation light (photons), ionizations, phonons,
etc are expected to be observed.• By combining multi. info., BG reduction is possible.
Scintillationlights
+ ++
- --
Ionizationsignals
Phononsignals
......
Bubblegeneration
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Expected energy spectrum of nuclear recoil, ~O(10keV)
• Coherent interaction with each nucleon in nuclei causes enhancement.
• Target nuclei with similar mass to DM is the best choice.
Si
Ge
XeSi
XeGe
Red: differential, Blue: integrated R.J.Gaitskell, Ann. Rev. Part. Sci., 54 (2004) 315.
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Another aspect: annual modulation• Due to a peculiar motion of the solar system
inside the galaxy, relative velocity to the rest frame of dark matter varies over a sidereal year.
• This causes the modulation of event rates and energy spectrum.
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Unknown: mass and cross section!
• Small mass: low energy threshold detector with light nucleus ~O(GeV/c2)
• Small cross section: massive and low BG detector ~O(1/day/ton) 3 orders/15years!
Mass of darkmatter particleUNKNOWN
cross sectionto nucleon UNKNOWN
True parameter
Detector with larger mass, longerexposure and lower background
Detector with smaller atomicnumber and low energy threshold
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Experiments all over the world >30!
XMASSNEWAGEPICO-LON
NIT
KIMS
PICASSOCDMS
CoGeNTCOUPP
DEAP/CLEANSIMPLEDMTPC
LUX
DAMA/LIBRAXENON
CRESSTIIEDELWEISS
ZEPLINDRIFTWARPArDMANAIS
MIMACROSEBUD
PANDAXCDEX
DM-Ice Not complete
TEXONO
Strong tension exists among experiments.DAMA, CoGeNT, CRESSTII XENON, CDMS
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1. DAMA/NaI (7yr), DAMA/LIBRA (6yr), 430tdAntonella, TAUP2011
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Positive signal of annual modulation• Radioactive pure NaI(Tl): scintillation only, no PID.• Strong signature of the annual modulation, ~9s
• A lot of criticisms at the beginning, but later serious study/consideration started (light DM, IDM, etc.).
• Influences of seasonal modulating cosmic muons? An unnatural background shape is in doubt.
by Sep. 2009Modulation of +/-2%
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2. CoGeNT (Ge) 140kgd• P-type point contact detector has
very low noise thus low energy threshold due to small cap. smaller-mass DM w/ ionization only
Science 332 (2011) 1144
PRL 101, 251301 (2008)
arXiV1106.06500
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Assume all the unknown events from DM
Mod. (c2/dof=7.8/12) 80%C.L. accept.Flat (c2/dof=20.3/15) 84% C.L. reject.
modulation is favored with 99.4% C.L.
Is the contamination of surfacebackground well controlled??
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3. XENON100, 4.8td
• Particle ID possible
• BG red.
Rafael,TAUP2011
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Observed data and calibration
• 3 events remained• 1.8+/-0.6BG expected (28%)
Observed data
Neutron source (causes nuclear recoil) calibration data
99.75% rejection line and3 sigma contour of NR
DM search window(8.4-44.6keVnr)
Nuc
lear
reco
il
e/
gam
ma
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Status of dark matter search
DAMA, Na, 3sDAMA, I, 3s
CoGeNT(Ge)90%5-7GeV
O. Buchmueller et al.CMSSM (68%, 95%)arXiv:1106.2529Including 2010 LHC
XENON100 (Xe)
CRESST 2s
• 3 orders of sensitivity improved over last 15 years!
CDMS (Ge)
+CDMS(LE), XENON10(LE)
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Recent “signals” of DM, axion, and n• 2000: DAMA experiment (Gran Sasso) started to
claim the observation of dark matter.
• 2005: PVLAS collaboration (INFN) axions?
• 2010/2011: CoGeNT (Soudan, US)• 2011: CRESST II (Gran Sasso) • 2011: OPERA (Gran Sasso, CERN) observation of
super-luminal neutrinos
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Recent “signals” of DM, axion, and n• 2000: DAMA experiment (Gran Sasso) started to
claim the observation of dark matter. >8s now
• 2005: PVLAS collaboration (INFN) axions? withdrawn
• 2010/2011: CoGeNT (Soudan, US)• 2011: CRESST II (Gran Sasso) • 2011: OPERA (Gran Sasso, CERN) observation of
super-luminal neutrinos
“Italian signals”
Further experimental check necessary
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XMASS experiment
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The XMASS collaborations
Kamioka Observatory, ICRR, Univ. of Tokyo :Y. Suzuki, M. Nakahata, S. Moriyama, M. Yamashita, Y. Kishimoto,Y. Koshio, A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi,K. Hiraide, A. Shinozaki, S. Hirano, D. Umemoto, O. Takachio, K. Hieda
IPMU, University of Tokyo : K. Martens, J.LiuKobe University: Y. Takeuchi, K. Otsuka, K. Hosokawa, A. MurataTokai University: K. Nishijima, D. Motoki, F. KusabaGifu University : S. TasakaYokohama National University : S. Nakamura, I. Murayama, K. FujiiMiyagi University of Education : Y. FukudaSTEL, Nagoya University : Y. Itow, K. Masuda, H. Uchida, Y. Nishitani,
H. TakiyaSejong University : Y.D. KimKRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee 41 collaborators,
10 institutes
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Kamioka Observatory
• 1000m under a mountain = 2700m water equiv.
• 360m above the sea• Low cosmic ray flux (10-5)• Horizontal access• Super-K for n physics and other experiments in
deep underground• KamLAND (Tohoku U.)
By courtesy of Dr. Miyoki
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XMASS experiment●XMASS ◎ Xenon MASSive detector for Solar neutrino (pp/7Be) ◎ Xenon neutrino MASS detector (double beta decay) ◎ Xenon detector for Weakly Interacting MASSive Particles (DM search)
• It was proposed that Liquid xenon was a good candidate to satisfy scalability and low background.
• As the first phase, an 800kg detector for a dark matter search was constructed.
Y. Suzuki, hep-ph/0008296
10ton FV (24ton) 2.5mSolar n, 0nbb, DM
in future
100kg FV (800kg) 0.8m, DMFirst phase
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Structure of the 800kg detector• Single phase liquid Xenon (-100oC, ~0.065MPa) scintillator
– 835kg of liquid xenon, 100kg in the fiducial volume– 642 PMTs– 5keVelectron equiv. (~25keVnuclear recoil) thre.
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BG reduction by self shielding effect
• Photo electric effect starts to dominate @500keV: strong self shielding effect is expected for low energy radiations.
E (keV)
Atte
nuat
ion
leng
th (c
m)
water
~O(500keV)
PhotoElectricEffect
Comptoneffect10cm
1cm LXe
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Event reconstruction
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Demonstration of the detector performance
• Calibration system– Introduction of radioactive sources
into the detector.– <1mm accuracy along the Z axis.– Thin wire source for some low energy g rays to avoid shadowing effect.
– 57Co, 241Am, 109Cd, 55Fe, 137Cs..
SteppingMotorLinearMotionFeed-through
Topphototube
~5m Gatevalve
4mmf
0.15mmf for 57Co sourceSource rod with a dummy source
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High light yield and good position resolution• 57Co source at the center shows a
typical response of the detector. High p.e. yield 16.0+/-1.0p.e./keV was obtained. Factor 3 higher than expected.
• The photo electron yield distribution was reproduced by a simulation well.
• Good position res. ~1cm obtained.
DATAMC
[keV]
Reconstructed energy
122keV
136keV59.3keV (W-Ka)
~4% rms
Dat
a at
var
ious
pos
ition
s
+15V
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Expected backgroundMajor backgroundmust come fromradioactivity in PMTs though we developed low BG PMTs.
Radioactive impurityinside liquid xenonalso must be low: 85Kr distillation Rn charcoal
BG ~ 10-4 /kg/keV/day is expected to be realized. (XENON100 ~0.5x10-4/kg/keV/day)
Background in unit mass
Very low BG at low energy
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Expected sensitivity
XENON100CDMSII
XMASS 2keVee thre. 100d
Black:signal+BGRed:BG
Expected energy spec.
1 year exposurescp=10-44 cm2
50GeV WIMP
Spin Independent
XMASS 5keVee thre. 100d
Initial target of the energythreshold was ~5keVee.Because we have factor ~3better photoelectron yield,lower threshold = smaller massdark matter may be looked for.
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Assembly of PMT holder and installation of PMTs
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Joining two halves
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P-01As of Sep. 2010
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Summary
• “Positive” signals by DAMA, CoGeNT, and CRESST-II (~10GeV, 10-40cm2) are around the detector threshold where our knowledge on the detector systematic and background are not established. Further experimental confirmations are necessary, and on going.
• The XMASS 800kg detector aims to detect dark matter with the sensitivity 2x10-45cm2 (spin independent case) with LXe.
• Commissioning runs are on going to confirm the detector performance and low background properties.– Energy resolution and vertex resolution were as expected. ~1cm
position resolution and ~4% energy resolution for 122keV g.