NEWS: Nuclear Emulsion Wimp SearchNatalia Di Marco Laboratori Nazionali del Gran Sasso - INFN

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Outline

• Directional Dark Matter Searches• The NEWS idea:

a novel approach to directional detection of DM• High Resolution Nuclear Emulsions: NIT • Detection Principle• NEWS R&D actvity• Design sensitivity

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Earth revolution gives seasonal modulation

Due to solar system movement in the galaxy, the WIMP Flux is expected to be not isotropic @earth.

A directional measurement would provide a strong signature and an unambiguous proof of the galactic origin of DM

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WIMP wind

Sun230km/s

Earth

Q

Recoil Nuclei direction

Scattered Wimp

WIMP cross-section with nuclei A2

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Directional Dark Matter Searches

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Directional Dark Matter Searches

Current approach: low pressure gaseous detector

• Targets: CF4, CF4+CS2, CF4 + CHF3 • Recoil track length O(mm)• Small achievable detector mass due to the low gas density

⇒Sensitivity limited to spin-dependent interaction

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DRIFT @ UKDM-TPC@ USA MIMAC@ FranceNEWAGE@ Japan

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Directional Dark Matter Searches

Use solid target: • Large detector mass• Smaller recoil track lenght O(100 nm)

very high resolution tracking detector

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Directional Dark Matter Searches

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Use solid target: • Large detector mass• Smaller recoil track lenght O(100 nm)

very high resolution tracking detector

Nuclear Emulsion based detector

acting both as target and tracking device

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Directional Dark Matter Searches

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Use solid target: • Large detector mass• Smaller recoil track lenght O(100 nm)

very high resolution tracking detector

Nuclear Emulsion based detector

acting both as target and tracking device

NEWS: Nuclear Emulsion WIMP searchItaly• Napoli Univeristy “Federico II”• LNGS – INFN• Bari University

Japan• Nagoya University

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Nuclear Emulsion

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AgBr crystal size 0.2-0.3 mm

After the passage of charged particles through the emulsion, a latent image is produced.The emulsion chemical development makes Ag grains visible with an optical microscope

A long history, from the discovery of the Pion (1947) to the evidence of nm nt oscillation in appearance mode (OPERA, 2014)

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Nuclear Emulsion

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Lighter nuclei (longer range at same recoil energy)

↓

Sensitivity to low WIMP mass

AgBr

ONC

A % Weight

I 126.9 0.8

Ag 107.9 28.5

Br 79.9 20.7

S 32.1 1.3

O 16.0 13.7

N 14.0 8.6

C 12.0 23.6

H 1.0 2.9

Chemical composition of nuclear emulsions

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Nuclear Emulsion

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Rang

e [n

m]

Recoil energy [keV]

Br range < 300 nm

WIMP velocity < 800 km/secTake e.g. MWIMP ~ 150 GeV/c2

Recoil energy < 500 keV

Max

reco

il en

ergy

[keV

]

WIMP mass [GeV/c2]

Br

Ag

OPERA emulsion films:Silver grain size 200 nm ̴� too large to record nanometric nuclear recoils

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NIT emulsion films: Nano Imaging Trackers

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Size

70 nm crystal 100 nm crystal 200 nm crystal

R&D

35 nm crystal

Range distribution [nm]

Recent developments

Natsume et al, NIM A575 (2007) 439

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Concept of readout: step 0

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Expansion of emulsion film

Chemical treatment

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Film expansion technique (T. Naka et al., NIMA581 (2007) 761)

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Concept of readout: step 0

Signal track

Random noise

Film expansion technique (T. Naka et al., NIMA581 (2007) 761)

Elliptical shape

Circular shape

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Expansion of emulsion film

Chemical treatment

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Concept of readout: step I

Scanning with optical microscope and shape recognition analysis

Automatic selection of candidate signals by optical microscopy. Full area scan. Resolution 200 nm (one order of magnitude better than the OPERA scanning system), scanning speed 20 cm2/h

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Test using 400 keV Kr ions

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Concept of readout: step I

Scanning with optical microscope and shape recognition analysis

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Direction detected!

θ

Test using 400 keV Kr ions

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Concept of readout: step I

Scanning with optical microscope and shape recognition analysis

Nucl.Instrum.Meth. A680 (2012) 12-17 

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Concept of readout: step II

Scanning with X-ray microscope of preselected zones

Pin-point check at X-ray microscope of candidate signals selected by optical readout. Resolution 30 nm ̴�

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330nm

236nm

486nm

600nm

Optical m

icroscope

X-ray microscope

Concept of readout: step II

Scanning with X-ray microscope of preselected zones

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330nm

236nm

486nm

600nm

Optical m

icroscope

X-ray microscope

Matching of recoiled tracks between Optical and X-ray microscope

Success rate of matching 572/579=99%

Concept of readout: step II

Scanning with X-ray microscope of preselected zones

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330nm

236nm

486nm

600nm

Optical m

icroscope

X-ray microscope

Matching of recoiled tracks between Optical and X-ray microscope

Success rate of matching 572/579=99%

Concept of readout: step II

Scanning with X-ray microscope of preselected zones

angular resolution [degrees]

optical microscope 31.4 +- 4.7 degree @original range: 150-250nm

X-ray microscope 16.8+-2.9 degree @original range: 150-250nm

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R&D activity

• NIT technology • Optical and X-ray read-out system• Intrinsic background measurement• Angular resolution measurement, neutron test beam• Full MC simulation

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R&D activity

• NIT technology • Optical and X-ray read-out system• Intrinsic background measurement• Angular resolution measurement, neutron test beam• Full MC simulation

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Sensitivity• Zero-background hypothesis• 90% C.L.• 100 nm tracking threshold• directionality information not included

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Conclusions

• A novel approach for directional Dark Matter searches is proposed in NEWS

• Novel nuclear emulsion technique with nanometric spatial resolution

• The use of a solid target would allow to explore the low cross section sector in the phase space indicated by recent direct search experiments but using a complementary an powerful approach

• NIT (Nano Imaging Tracker)• Read-out system based both on optical (200 nm resolution) and

X-ray microscopy (30 nm resolution)

… from the R&D to the experiment in few years

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