Future Planning of Dark Matter Search with Nuclear Emulsion Naka 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 velocity strong 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/cm 3 sunearth Dark 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 Strongest limit by XENON DAMA region They 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 dR/dQ [event/kg/keV/day] time [months] only 3 ～ 4% Vearth=v±30km/sec Long cycle and few variation

center of galaxy WIMPs velocity V W S 200km/sec E V rel = V W + 200km/sec VWVW detector 200km/secWIMPs EE 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 Sun 220km/sec Earth NIT 地下で NIT を赤道儀に載せ地球の回転を打ち消す WIMP 夏 冬 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/cm 3 )‏ Good dark matter detector!! WIMP velocity in earth frame But… any hundred nm! Range [nm] Velocity [km/sec]

High resolution emulsion (Nano Imaging Tracker:NIT)‏ OPERA NIT 200nm NIT:AgBr crystal size ~40nmOPERA:AgBr crystal size ~200nm 11 AgBr/μm2.3 AgBr/μm 5 times resolution for OPERA!

Recoil nuclear test of NIT ⇒ implant 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 nm 600 nm Kr km/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/μm 2 measure 0.17±0.02 tracks/μm 2 600keV Kr track data Dose 0.05±0.02 ions/μm 2 measure 0.06±0.01 tracks/μm 2

Optical microscope image masked Dark Field Image of Light Microscope look like Kr signal and random fog Dose = 10 8 /cm 2 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 emulsion Kr ion Range ~100nm order swell Expected range ~ μm order Use the swelling characteristic of emulsion NIT NIT optical microscope slice

200keV 400keV600keV 未照射 random fog

3.6±0.8 μm3.1±0.8 μm1.5±0.5 μm Expansion Kr track data by swell technique 200keV400keV600keV Rate of number of grain [%] range [μm] Kr 600keV number of grainKr 400keV number of grainKr 200keV number of grain Expanded track have equivalent information to electromicroscope.

background Main background for WIMP search with NIT Inside background ・ 14 C ・ random fog ⇒ chance coincidence ( ※ outside background ⇒ shielding )‏ β ・ γbackground ⇒ reject by sensitivity control Recoil Nuclear dE/dx Electron dE/dx =100 ～ 1000

Normal Ｎ ＩＴ No sensitized ＮＩ Ｔ ＨＡ sensitized ＮＩ Ｔ 10μm ※ αray track 10μm Sensitivity control of NIT Halogen Accepter sensitized ⇒ sensitivity between no sensitized NIT and normal NIT β ・ γrejection power( 241 Am 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!