The recent results from kims
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The recent results from KIMS . ?. Seung Cheon Kim (Seoul National University) for KIMS collaboration. At Yangyang beach, looking for something in the swamp of particles and waves. KIMS(Korea Invisible Mass Search) collaboration. Dark matter ? . Rotation curve for Galaxy .

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The recent results from KIMS

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The recent results from kims

The recent results from KIMS

?

SeungCheon Kim

(Seoul National University)

for KIMS collaboration

At Yangyang beach,

looking for something

in the swamp of particles and waves.

Dark Side of the Universe 2011


Kims korea invisible mass search collaboration

KIMS(Korea Invisible Mass Search)collaboration


Dark matter

Dark matter ?

Rotation curve for Galaxy

X-ray from Hot cluster

Bullet cluster

Not visible, but gravitationally evident!

Parameters of CDM by WMAP


The recent results from kims

If dark matter is WIMP,

It will deposit around 10 keV in the absorber!

Thermal signal

Scintillation, e-h pair

Produced from nuclear Recoil(NR)

But, its event rate will be very small.

Dark Side of the Universe 2011


The recent results from kims

KIMS experiment ?

CsI(Tl) scintillator

Well-known, widely-used technique

Large atomic number, Cs (133), I (127)

Good for A2 scaling

High spin expectation value for proton

Sensitive to SD interaction

Discrimination of nuclear recoil

events by PSD analysis

But, some inherent backgrounds

like Cs134, Cs137, Rb87

Dark Side of the Universe 2011


Detector design

Detector design

One detector module : one CsI Crystal + 2 PMTs

Crystal size: 8x8x30 cm3 (8.7 kg)

(Beijing Hamamatsu Photon Techniques Inc.)

PMT : 3” PMT (9269QA),

Quartz window,

RbCs photo cathode

(green extended)

Event window is 40µs.

Digitized with 400MHz FADC

Am241 calibration

13.9keV Np L X-ray

17.8keV Np L X-ray

20.8keV Np L X-ray

26.35keV gamma

Cs, I X –ray escape

59.54 gamma

5-6 p.e /keV


The recent results from kims

Detector array

3 x 4 detector array

The total mass : 103.4 kg

Multiple hit events

=> references for calibration

E of det10

134Cs

E [keV]

β-

4+

1969.87

27.3%

3+

1643.28

2.50%

4+

1400.55

70.1%

1167.93

2+

0.033%

2+

604.70

0.10%

0+

0.0

134Ba

Total E except det10

Dark Side of the Universe 2011


The recent results from kims

Neutron shield(30cm mineral oil)

KIMS Detector system

Lead shield (15cm)

Polyethylene(5cm)

Copper

(10cm)

CsI(Tl) Scintillator

Neutron detector

Muon detector

(Neutron sheild)

N2 gas flow inside the Cu shield


Experimental site

Experimental site

YangYang underground Lab(Y2L)

=>Located in Yangyang pumped storage power plant

=>700m minimum depth, muon flux : 2.7 x 10-7/cm2/s

=>accessible by car (tunnel~2km)


The recent results from kims

Surface alpha (SA) background

Electron recoil events

4th WCU workshop 090908


The recent results from kims

Study of SA events

using Rn progeny contaminated crystal

Sides are wrapped by teflon

PMTs

CsI(Tl) crystal

A: Rn progeny contaminated

,exposed to Rn gas for 4 days

B:clean

A

B

Aluminum foil

t=2m x 3 layers

gamma

SA

Tagged as alpha at B

Dark Side of the Universe 2011


The recent results from kims

Comparison of PSD parameter, logrmt10

NR

ER

SA

Dark Side of the Universe 2011


Event selection

PMT

PMT

Clean acryl box

Event selection

Period: September 2009 – August 2010

=> 317.15 live days

PMT noise, muon-coincident events, tail events,

multiple hit events rejected

tail events

Compton events


The recent results from kims

The estimation of the NR events rate

Pdf = f0 x FNR + f1 x FSA + (1-f0-f1) x Fgamma

The posterior pdffor f0 & f1 is obtained

from Bayesian analysis method.

Dark Side of the Universe 2011


The recent results from kims

The estimated NR event rates for 12 detectors

90 % limit

68 % interval

Dark Side of the Universe 2011


The recent results from kims

The overall NR events rate

det0, 8, 11 excluded

Total exposure: 24524.3 kg days

No meaningful excess of NR events is not observed !!!

Dark Side of the Universe 2011


The recent results from kims

KIMS NR event rates

& DAMA/LIBRA annual modulation amplitude

  • The annual modulation amplitude from DAMA

  • At 2-4keV, 0.0183±0.0022 counts/day/kg/keV

  • At the corresponding energy range (3.6-5.8 keV)

  • in KIMS, (QF for DAMA =0.08 adopted)

  • The 90 % C.L limit is 0.0098 counts/day/kg/keV

  • This is well below the DAMA modulation amplitude.

  • Any scenario with Iodine for DAMA is not consistent

  • with KIMS results !!!


The recent results from kims

KIMS & DAMA in iDM model

Cs

I

Expected spectrum for iDMin KIMS detector

=> M=70 GeV, δ=116keV, vesc=500 km/s,

ve=235km/s, σ=0.93e-3 pb

For 70 GeV mass WIMP


The recent results from kims

The new exclusion limits from KIMS

Spin-dependent

proton interaction

Spin-Independent interaction

Dark Side of the Universe 2011


The recent results from kims

Annual modulation study

2 year of data have been obtained in the stable conditions.

Modulation analysis on going

- w/o PSD

- 2keV threshold

Stability of temperature, gain

etc. has been monitored

Low energy contribution

from Cs-134, the time varying

background

Multiple hit events

Dark Side of the Universe 2011


Summary

Summary

24524.3 kg days data was analyzed.

Surface alpha background were identified.

No meaningful excess of NR events were found.

Our 90 % limit for NR events is well below the

amplitude observed by DAMA/LIBRA, disfavoring

any Iodine interpretation.

New improved exclusion limits for WIMP-nucleon interaction were presented.

Annual modulation analysis results will be done soon.

Dark Side of the Universe 2011


The recent results from kims

?

Nothing found yet…

Dark Side of the Universe 2011


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