(direct) Dark Matter Searches andXMASS experiment

DM search: status, prospects and difficulties for large scale

experimentsXMASS experiment

S. MoriyamaKamioka ObservatoryInstitute for Cosmic Ray ResearchMarch 3rd 2007, KEKTC7

A lot of evidences on the existence of DM1. Orbital velocities of galaxies in clusters2. Rotational speed of galaxies3. Gravitational lensing of background objects by

galaxy clusters4. Temperature distributions of hot gas in galaxies

and clusters of galaxies5. CMB power spectrum analysis in WMAP6. The Bullet cluster7. Large scale map for dark matter8. …

Dark Matter in the Universe A lot of evidences on the existence of DM

WMAP Cosmic Microwave Backgroundpower spectrum decomposed matter, cold dark matter, and dark energy NASA

The Bullet cluster: NASARed: ordinary matter from X-ray Blue: mass from gravitational lensing

All of them are astrophysical observations. “Direct detection” is an urgent issue now.

WIMP Dark Matter

Particles thermally generated at high temperature decouple when the expansion rate ~ the interaction rate.

Weakly interacting, heavy, neutral, and stable particles can be CDM.

(WIMPs != SUSY here)E.W. Kolb and M.S. Turner, The Early Universe

X=m/Temperature (time )

Com

ovin

g nu

mbe

r de

nsity

Nequillibrium

Increasing<Av>

Dark Matter in the Milky Way

Also, the Milky Way (our galaxy) has a large amount of Dark Matter.

R.P.Olling and M.R.Merrifield MNRAS 311, 369- (2000)

Buldge

Steller disk

Dark Halo

Motion of WIMPs around us

Earth

Sun

Annual, sidereal modulation

DM density ~0.3GeV/cc100GeV WIMPs 1 WIMP / 7cm cubic, =105/cm2/sec

The solar system is moving at ~230km/sec.The earth is moving at ~30km/sec.The earth is rotating.

WIMPs are randomlymoving with Maxwelldistribution <v>~270km/sec

“Wind” of Dark Matter

(direct) Detection method Since they are neutral and stable, what we

can expect is only a collision with ordinary matter.

Electron recoil does not give enough energy but nuclear recoil gives ~100keV if mDM~O(100GeV).

Dark Matterparticles

Energy deposit

What is the best target?Recoil spectrum (spin independent)

Ge and Xe, and Ar give similar rates. Annual modulation should be seen.

Si

Ge

XeSi

XeGe

Red: differential, Blue: integrated

Target Xe

Assuming quenchingfactor of 0.2

June

Dec.

R.J.Gaitskell, Ann. Rev. Part. Sci., 54 (2004) 315.

WIMP mass 100GeV

Diff.~6%

Candidate: Neutrarino in the Supersymmetric Model

SUSY solves the hierarchy problem, stability of boson mass, and it can predict the gauge coupling unification. The prime paradigm beyond the standard model.

Even if SUSY particles are discovered in LHC, direct detection of DM should be done INDEPENDENTLY.

SM particles SUSY particles

Quark

Lepton

Higgs

Gauge particles

uu dd cc ss tt bb

ee ee

gg WW ZZ

uu dd cc ss tt bb~ ~ ~ ~ ~ ~

ee ee ~ ~ ~ ~ ~ ~

HH++ HH-- HH1100 HH22

00~ ~ ~ ~

gg WW ZZ00~ ~ ~ ~

AA00HH++ HH-- HH1100 HH22

00

Neutralino

(1pb = 10-36cm2 )

Expected cross section to nucleon

Large space of SI for proton.

SNOWMASS benchmark, many of them: 10-

8-10-10pb

General MSSM

10-6

10-12

SI f

or p

roto

n (p

b)

100 400 700 M(GeV)

Y.G.Kim et al. 2002

10-8

10-10

Mission in the real world

Once we make detector, we have 10~100Hz background by ambient gamma rays and internal radioactive contaminations, and neutrons.

What we need to realize is “1count/100day detector”.

108-9 reduction needed

DM Searches: past

NaI(Tl) at Gran SassoExposure 107 ton dayAnnual modulation over 7 years

6.3sigma C.L. annual modulation2-6keV data:0.02000+/-0.0032 cpd/kg/keVT0=140+/-22 days (exp. 152.5th day)T=1.00+/-0.01 year

No modulation: 7x10-4 (2/d.o.f.=71/37)

DAMA: NaI(Tl) scintillator

LIBRA experiment will reject/confirm the result.

astro-ph/0307403

DM searches: recent, CDMS (Ge)

Blind analysis done. World best limit obtained: ~O(kg)

4x250g Ge2x100g Si

BG from, e: EQ~EP

Signal : EQ~0.3EP

Ionaization EQ

Bolometric EP

Rise time of Ep, timing diff. btw EP & EQ

1st run Oct.03-Jan.04 2nd run Feb.04-Aug.04

Recoil energy (keV) Recoil energy (keV)

BG band

Signal band~E

Q/E

P

CDMS to SuperCDMS:25kg seems to be straight forward

DM searches: XENON (2 phase LXe)

XENON10: 10kg target first results soon! XENON100: 100kg target 2007-2009 construction

M. Yamashita IDM2006

Liquid xenon scintillator with charge coll.

Rare gas liquid: scale up, purification easy

DM searches: WARP/ArDM (Liquid Ar)

P.Benettiastro-ph/0701286

S2/S1 + difference of scintillation waveformfor e and nuclear recoil e n

Integrated waveforms

1s

L

og(S

2/S

1)

n-lik

e

e-lik

e

Pulse shepe parameter e-like n-like

CDMSII

WARPNeed to remove 39Ar (0.8Bq/kg)100 liter detector soon?

Future: larger scale Exp.

General MSSM

10-6

10-8

10-10

10-12

SI f

or p

roto

n (p

b)

100 400 700 M(GeV)

Y.G.Kim et al. 2002

B. SadouletKEKTC6

~4events/100ton/year10-12 pb is really

challenging!!

~4events/100kg/yearXe recoil E >25keV

+5-10year 10-9 ~ -10pb

CDMSII (current)Sorry for approximate line

2007 CDMS 10-7pbDAMA

2003 DAMA 10-6pb

10-12pb detection requires Super-K @ keV

Super-K

KamLAND (>0.8MeV)

Heidelberg Moscow

Kamioka Ge

ZEPLIN before PSD cut

DM signal for LXe100GeV 10-6pbQF=0.2

DAMANaI

Eve

nts/

kg/k

eV/d

ay

BG requiredFor 10-12pb

CDMSII

Atm, solar neutrino NC nuclear recoil appear

Difficulties appear ~10-9-10-10pb Scale-up is always accompanied with new bac

kground sources which are caused by:1. Low E threshold2. Surface effect3. Impurities in the targets4. Insufficient rej. eff.5. Neutron background

Small signals Surface & rays 39Ar, 85Kr Large # of BG >108

muon, parts inside

neutron

?

Target (Ge, LAr, LXe)Neutron BG will bedominated <10-9pb~Full target schemei.e. Ge, XENON, WARPsingle neutron eventscannot be discriminated

Neutron background

neutrone,

Strategy for larger target, high sensitivity

XMASS!

Neutron shielding by large amount of target itself.

Currently, “gamma rejection” is extensively studied. CDMS, XENON, and WARP have good discriminations with multiple information.

However, <10-9pb, neutron will be most serious BG. It cannot be discriminated. N. Spooner, DM2004

MC: outside Xenon

Blue : γ trackingPink : whole liquid xenonDeep pink : fiducial volume

U-chain gamma rays

XMASS (liquid Xe sci.) at Kamioka Self shielding with large target

for gamma rays

80cm dia.800 kg

All volume20cm wall cut30cm wall cut (10ton FV)

Large self-shield effect

External ray from U/Th-chain

BG can be efficiently reduced in < 500keV low energy region

1MeV0 2MeV 3MeV

250cm dia.23 ton

BG

nor

ma

lize

d b

y m

ass

Self shield for fast neutrons (5MeV)

Assumption: irreducible BG is only single neutron scattering

1/100 reduction is possible in 30cm thickness.

Red: single recoil

250cm dia.23 ton

Fiducialvolume

Single recoil Vertex distributionEvis>5keV

0 60 120Distance from the center (cm)

FV

# of

eve

nts

(cm

-3)n

100kg PrototypeFV 3kg

800kg detectorFV 100kg

23 ton detector, FV 10t

～ 30cm ～ 80cm ～ 2.5m

R&D

Dark matter search

Multipurpose detector

(solar neutrino, …)

“Full” photosensitive, large volume detector

Realize ~FULL COVERAGE

Neutron BGnot serious

Neutron shield30cm outer layer >1/100

Vertex reconstructionLarge photoelectronYield can be obtained~5 p.e./keV

Accurate vertexReconstruction basedon light pattern possible

Liq. Xe 　(31cm)3

MgF2 window

54 2-inch low BG PMTs

16% photo-coverage

HamamatsuR8778

Confirmation with a prototype detector done.

Demonstration with a prototype detector I

DATA

MC

A B C

+++Reconstruction works well

Data well reproduced by MC

30cm cube

Gamma ray injection from collimators

Confirmed Self shielding

>2 orders of magnitude agreementsGamma rays

Z= +15Z= -15

137Cs: 662keVDATAMC

PMTsaturation

-15 +15cm -15 +15cm

~1/200

~1/10

Reconstructed Z

Arb

itrar

y U

nit

10-1

10-2

10-3

10-4

10-5

10-1

10-2

10-3

10-4

10-5

60Co: 1.17&1.33MeV DATA MC

Reconstructed Z

Demonstration with a prototype detector II

Detail design of the 800kg detector

GEANT4 base simulation done

6cm RMS for 5keV @ boundary of FV Good performance

Background of the 800kg detector

Background origins

Neutrons: enough by

water shield

PMT rays: low BG PMT

Radioactive impurities:

distillation

PMT

n

RI in LXe

Background from PMTs (238U )

1.8 mBq-238U/PMT, most clean PMT ever made (achieved) c.f. usual “low” activity PMT ~O(1Bq/PMT)

BG <100keV 5cm self shield: ~10-3 /day/kg/keV 10cm self shield: ~10-4 /day/kg/keV 20cm self shield: ~10-5 /day/kg/keV (2events/100kg/5keV/year)

Fiducial cutRed: 100kgN

orm

aliz

ed b

y vo

lum

e(d

ay-1kg

-1ke

V-1)

Radioactive contaminationMeasured with the prototype detector

U, Th, Kr near to the goal. Within reach.

Internal origin of backgroundTarget values to achieve our goal

238U: < 1x10-14 g/g

232Th: < 2x10-14 g/g

85Kr: < 1ppt from reactors

(9±6) x10-14 g/g Further reduction by filter< 23 x10-14 g/g Upper limit, use filter3.3±1.1 ppt Distillation system (original)

Sensitivity of the 800kg detector

x 100 sensitive than CDMSII

XMASS FV 0.5ton year (100kg, 5yr)3 discovery

W/O any pulse shape info.

Plots exept for XMASShttp://dmtools.berkeley.eduGaitskell & Mandic

106

104

102

1

10-2

10-4

103

Near future ~5years

Ge, Ar and Xe go down to 10-9pb

Aim to detect DM ~2010

10-6

10-8

10-10

10-12Cro

ss s

ectio

n to

nuc

leon

(pb

)

+10yr, sensitivity of DM exp.

<10-10pb ~10ton volume Thick outer

shield (~30cm) will reduce neutron BG for further >100!

10-6

10-8

10-10

10-12Cro

ss s

ectio

n to

nuc

leon

(pb

)

Summary Direct detection of DM, WIMPs, is an urgent issue. Solid state & Noble gas liquid are the world trend fo

r large scale experiments. Search with <10-9pb, neutron will be most serious b

ackground, and it should be shielded by the target volume itself. XMASS

R&D efforts for XMASS done. XMASS at Kamioka is going to improve factor 100 i

n the sensitivity (~10-9pb). Serious competition in the world. Need to start now!