Recent progress of direct dark matter detectionS. Moriyama Institute for Cosmic Ray Research, University of TokyoOct. 8th, 2011 @ FPUA2011, Okayama, Japan

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

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.

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

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.

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.

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

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

1. DAMA/NaI (7yr), DAMA/LIBRA (6yr), 430tdAntonella, TAUP2011

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%

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

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??

3. XENON100, 4.8td

• Particle ID possible

• BG red.

Rafael,TAUP2011

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

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)

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

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

XMASS experiment

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

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

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

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.

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

Event reconstruction

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

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

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

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.

Assembly of PMT holder and installation of PMTs

Joining two halves

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P-01As of Sep. 2010

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.