Recent progress of - PowerPoint Presentation

Slide1

Recent progress of direct dark matter detection

S. Moriyama

Institute for Cosmic Ray Research, University of Tokyo

Oct. 8

th

, 2011 @ FPUA2011, Okayama, JapanSlide2

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 matter

Annihilation

Scattering

1/temperature ~ time

Comoving

number densitySlide3

How much dark matter around us?

It can be estimated by measuring rotational curve of the galaxy. Local density ~ 0.3GeV/cc ~average x 10

5

Isothermal, Maxwell distribution

(<v> ~230km/s, <

b>~10-3).

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

Buldge

Steller disk

Dark Halo

These dark matter particles are expected to cause nuclear recoils even in underground lab.Slide4

Signals after nuclear recoils

Small energy depositions (m

p

<v>2/2 < 1keV), rare.Scintillation light (photons), ionizations, phonons, etc are expected to be observed.

By combining multi. info., BG reduction is possible.

Scintillation

lights

+

+

+

-

-

-

Ionization

signals

Phonon

s

ignals

.

.....

Bubble

generationSlide5

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

Xe

Si

Xe

Ge

Red: differential

,

Blue: integrated

R.J.Gaitskell, Ann. Rev. Part. Sci., 54 (2004) 315.Slide6

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.Slide7

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 dark

matter particle

UNKNOWN

cross section

to nucleon UNKNOWN

True parameter

Detector with larger mass, longer

exposure and lower background

Detector with smaller atomic

number and low energy thresholdSlide8

Experiments all over the world >30!

XMASS

NEWAGE

PICO-LON

NIT

KIMS

PICASSO

CDMSCoGeNTCOUPPDEAP/CLEAN

SIMPLEDMTPCLUX

DAMA/LIBRAXENONCRESSTII

EDELWEISSZEPLINDRIFTWARPArDM

ANAISMIMACROSEBUD

PANDAXCDEX

DM-Ice

Not complete

TEXONO

Strong tension exists among experiments.

DAMA, CoGeNT, CRESSTII

 XENON, CDMSSlide9

1. DAMA/NaI (7yr)

,

DAMA/LIBRA

(6yr), 430td

Antonella

, TAUP2011Slide10

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. 2009

Modulation of +/-2%Slide11

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)

arXiV1106.0650

0Slide12

Assume all the unknown events from DM

Mod. (

c

2/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 surface

b

ackground well controlled??Slide13

3. XENON100, 4.8td

Particle ID possible

 BG red.

Rafael,

TAUP2011Slide14

Observed data and calibration3 events remained

1.8+/-0.6BG expected (28%)

Observed data

Neutron source

(causes nuclear recoil)

calibration data

99.75% rejection line and

3 sigma contour of NR

DM

search window

(8.4-44.6keVnr)

Nuclear recoil

 e/gammaSlide15

Status of dark matter search

DAMA, Na, 3

s

DAMA, I, 3

s

CoGeNT

(

Ge)90%5-7GeV

O.

Buchmueller et al.CMSSM (68%, 95%)arXiv:1106.2529Including 2010 LHC

XENON100 (Xe

)CRESST 2

s

3 orders of sensitivity improved over last 15 years!CDMS (

Ge)+CDMS(LE), XENON10(LE)Slide16

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 neutrinosSlide17

Recent “signals” of DM, axion, and n

2000: DAMA experiment (Gran

Sasso

) started to claim the observation of dark matter.

 >8s

now2005: 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 necessarySlide18

XMASS experimentSlide19

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.Liu

Kobe University: Y. Takeuchi, K. Otsuka, K. Hosokawa, A. Murata

Tokai University: K. Nishijima, D. Motoki, F. Kusaba

Gifu University： S. Tasaka

Yokohama National University： S. Nakamura, I. Murayama, K. Fujii

Miyagi 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 institutesSlide20

Kamioka Observatory

1000m under a mountain = 2700m water equiv.

360m above the sea

Low cosmic ray flux (10-5)

Horizontal accessSuper-K for n

physics and other experiments in deep underground

KamLAND (Tohoku U.)

By courtesy of Dr. MiyokiSlide21

XMASS experiment

●

X

MASS

◎

Xenon MASS

ive 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 s

calability 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) 2.5m

Solar

n

, 0

nbb

, DM

in future

100kg FV (800kg)

0.8m,

DM

First phaseSlide22

Structure of the 800kg detector

Single phase liquid Xenon (-100

o

C, ~0.065MPa) scintillator835kg of liquid xenon, 100kg in the

fiducial volume642 PMTs

5keVelectron equiv. (~25keVnuclear recoil

) thre.Slide23

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

)

Attenuation length (cm)

water

~O(500keV)

Photo

Electric

Effect

Compton

effect

10cm

1cm

LXeSlide24

Event reconstructionSlide25

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.57

Co, 241Am, 109

Cd, 55Fe, 137

Cs..

Stepping

Motor

Linear

Motion

Feed-

through

Top

photo

tube

~5m

Gate

valve

4mm

f

0.15mm

f

for

57

Co source

Source rod with a dummy

sourceSlide26

High light yield and good position resolution

57

Co 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.

DATA

MC

[

keV

]

Reconstructed energy

122keV

136keV

59.3keV (W-Ka)

~4% rms

Data at various positions

+15VSlide27

Expected background

Major background

m

ust come from

radioactivity in PMTs though we developed low BG PMTs.

Radioactive impurityinside liquid xenona

lso 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 energySlide28

Expected sensitivity

XENON100

CDMSII

XMASS

2keVee

thre

. 100d

Black:signal+BG

Red:BG

Expected energy

spec.

1 year exposure

s

c

p

=10

-44

cm

2

50GeV WIMP

Spin Independent

XMASS

5keVee

thre

. 100d

Initial target of the energy

t

hreshold was ~5keVee.

Because we have factor ~3

better photoelectron yield,

lower threshold = smaller mass

dark matter may be looked for.Slide29

Assembly of PMT holder and installation of PMTsSlide30

Joining two halvesSlide31

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P-01

As of Sep. 2010Slide32

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.