Future Planning of Dark Matter Search with Nuclear Emulsion

Naka Tatsuhiro@ Nagoya university

Evidence of Dark Matter

◎Rotation velocity of Galaxy

◎Gravitational Lens

◎Cosmic Microwave 　Background(CMB) etc

Candidate of Dark matter

• Cold Dark Matter = non-relativistic velocitystrong candidadte

⇒Weakly Interacting Massive Particle(WIMP) Ex) Super Symmetry theory ⇒Neutralino

• Hot dark matter = relativistic velocity

ex) neutrino ν 　 　 　 　 　

They can’t contribute galaxy form.

Rotation curve of Our Galaxy

solar system Dark Matter exist in our Galaxy!!

vv

Dark Matter Energy Density 0.3GeV/cm3

sunearthDark matter halo

WIMP distribute Maxwellian

WIMP detection

230km/sec

WIMP sea

・ ionization

・ heat

・scintillation

elastic scattering

Nuclear recoil detect!

WIMP has no electronic charge

detector

Status of dark matter search group principle of detection underground exposureCDMS semicondactor bolometer・ Soudan 34kg day・CREST Gransasso

EDELWISE Frejus 62kg day・XMASS scintillation Kamioka (800kg)DAMA Gransasso 107731kg day・

XENON scintillation(2phase) Gransasso 136kg day・WARP 100kg day・

NEWAGE gas TPC(direction) Kamioka 0.23kg day・DRIFT Boulby (167g)

Strongest limit by

XENON

DAMA regionThey insisted “discovery”

Process of discovery for almost detector

Another detector look only energy spectrum.

They can’t distinguish signal from final neutron background

annual modulation

0 20 40 60 80

0.0425

0.045

0.0475

0.05

0.0525

0.055

0.0575

0.06

dR

/dQ

[ev

ent/

kg/k

eV/d

ay]

time [months]

only 3～ 4%

Vearth=v±30km/sec

Long cycle and few variation

center of galaxy

WIMPs velocity VW

S

200km/secE

Vrel = VW + 200km/sec

VW detector 200km/secWIMPs

E

E

Detection of directional of WIMP wind

WIMP wind have directional velocity in the earth frame

Signal direction vary 24h cycle high reliability⇒

=100～ 1000km/sec

Principle for Detection of WIMPs with NIT

Earth

Sun220km/sec

EarthNIT

地下で NITを赤道儀に載せ地球の回転を打ち消す

WIMP

夏

冬

WIMP

Ag

Br

AgBr crystal

WIMPs wind

Range of recoil nuclear ～100nm

Ag recoil nuclear

Maxwell 　　　　　　　　　　　　　　　　　　　　　　　　速度分布 のWIMP

　　ゼラチン H,C,N,O,S

WIMPs wind ~ 230km/sec

Recoil energy ~ 100keV

(if WIMPs mass ~ 100GeV)

NIT

Nuclear emulsion• High resolution tracking detector• High density (OPERA ~2.8g/cm3)

Good dark matter detector!!WIMP velocity in earth frame But…

any hundred nm!

Ran

ge [

nm]

Velocity [km/sec]

High resolution emulsion (Nano Imaging Tracker:NIT)

OPERA NIT

200nm

NIT:AgBr crystal size ~40nmOPERA:AgBr crystal size ~200nm11 AgBr/μm2.3 AgBr/μm

5 times resolution for OPERA!

Recoil nuclear test of NITimplant low velocity Kr ion⇒

Top view

Side view

イオンビーム

チェンバーの真空はそのままに

７つのサンプルに照射できる

サンプル台が回転

フィルム

サイズ 7cm×3cm

乳剤層の厚み

NIT： 5μm

OPERA： 20μm

200 nm600 nm

Kr3+ 1200km/s (600keV) Kr+ 680km/s (200keV)

NIT no development

Tracking test by low velocity Kr

Supposition Br recoil SEM image

200keV Kr track data

Dose 0.18±0.02 ions/μm2

measure 0.17±0.02 tracks/μm2

600keV Kr track data

Dose 0.05±0.02 ions/μm2

measure 0.06±0.01 tracks/μm2

Optical microscope imagemasked

Dark Field Image of Light Microscope

look like Kr signal and random fog

Dose = 108/cm2

Random fog

Interaction of WIMP is very weak

We need heavier detector

Scanning and analysis are needed track selector

We must distinguish the kr signal(Nuclear recoil) from random fog.

Idea: expand short range track until μm

Kr ion exposure

Swell technique of NIT emulsionKr ion

Range ~100nm order

swell

Expected range ~ μm order

Use the swelling characteristic of emulsion NIT

NIT

optical microscopeslice

200keV 400keV 600keV 未照射

random fog

Kr 600keV number of grain distribution

0

5

10

15

20

25

30

35

40

number　of　grain

rate　for　all　

track　

[%]

expansion　Kr　　dataSEM　data

expansion　Kr　　data 0 5.4455 15.842 24.257 25.248 20.792 5.9406 2.4752

SEM　data 5 15 37.5 22.5 10 7.5 2.5

2 3 4 5 6 7 8 9

Kr400keV number of grain

0

5

10

15

20

25

30

35

40

45

50

grai

n ra

te fo

r to

tal t

rack

gra

in [

%]

expansion　track　dataSEM　data

expansion　track　data 0 22.449 43.878 21.429 7.1429 2.0408

SEM　data 18.75 46.9 25 6.25 3

2 3 4 5 6 7

Kr 200keV number of grain

0

10

20

30

40

50

60

70

number　of　grain

rate

o

f n

um

be

r o

f grain

fo

r all trac

k [%

]

expansion　KrdataSEM　data

expansion　Kr　data 53.8043478 40.2173913 5.97826087

SEM　data 63 34.7 2.1

2 3 4

3.6±0.8 μm3.1±0.8 μm1.5±0.5 μm

Expansion Kr track data by swell technique

200keV 400keV 600keV

Rat

e of

nu

mb

er o

f gr

ain

[%

]

Rat

e of

nu

mb

er o

f gr

ain

[%]

Rat

e of

nu

mb

er o

f gr

ain

[%

]

2 3 4 2 3 4 5 6 72 3 4 5 6 7 8 9

range [μm] range [μm] range [μm]

Kr 600keV number of grain Kr 400keV number of grain Kr 200keV number of grain

Expanded track have equivalent information to electromicroscope.

backgroundMain background for WIMP search with NIT

Inside background

　　　　　　　　・ 14C

　　　　　　　　・ random fog chance coincidence ⇒

( outside background shielding )※ ⇒

β・ γbackground ⇒reject by sensitivity control

Recoil Nuclear dE/dx

Electron dE/dx=100～ 1000

Normal ＮＩＴ

No sensitizedＮＩＴ

ＨＡ sensitized ＮＩＴ

10μm10μm

※αray track

10μm

Sensitivity control of NIT

Halogen Accepter sensitized sensitivity between no ⇒sensitized NIT and normal NIT

β・ γrejection power(241Am γray test)

⇒Rejection < 10E-5 (manual determination)

Summery

• Detection of directional WIMP wind is very important

• NIT have power of tracking nuclear recoil

• By expansion technique, any 100 nm track was recognized by optical microscope.

• By sensitivity control, may be reject β background more than 10E-5

Prospect• Development scanning system for NIT• More detail background study• Development low background NIT ex)substitute of gelatin (PVA etc) more fine grain etc• NIT facility in underground⇒start experiment by prototype detector

Application by NIT・ Neutron monitor・ heavy ion detector・ other low background physics etc

NIT has high potentiality!