NEWS: Nuclear Emulsion Wimp Search
Natalia Di Marco
Laboratori Nazionali del Gran Sasso - INFN
N. Di Marco
• 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
Moriond Cosmology - March 2014
Outline
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Earth revolution gives seasonal modulation
Earth
WIMP wind
Due to solar system movement in the galaxy, the
WIMP Flux is expected to be not isotropic @earth.
Sun
230km/s
N. Di Marco
A directional measurement would provide a
strong signature and an unambiguous proof of the
galactic origin of DM
Moriond Cosmology - March 2014
Directional Dark Matter Searches
Scattered Wimp
Q
WIMP cross-section
with nuclei  A2
3
Recoil Nuclei direction
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
N. Di Marco
Current approach:
Moriond Cosmology - March 2014
Directional Dark Matter Searches
4
NEWAGE@ Japan
DM-TPC@ USA
DRIFT @ UK
MIMAC@ France
N. Di Marco
Use solid target:
• Large detector mass
• Smaller recoil track lenght O(100 nm)
 very high resolution tracking detector
Moriond Cosmology - March 2014
Directional Dark Matter Searches
5
N. Di Marco
Use solid target:
• Large detector mass
• Smaller recoil track lenght O(100 nm)
 very high resolution tracking detector
Moriond Cosmology - March 2014
Directional Dark Matter Searches
Nuclear Emulsion based detector
acting both as target and tracking device
5
N. Di Marco
Use solid target:
• Large detector mass
• Smaller recoil track lenght O(100 nm)
 very high resolution tracking detector
Moriond Cosmology - March 2014
Directional Dark Matter Searches
Nuclear Emulsion based detector
acting both as target and tracking device
NEWS: Nuclear Emulsion WIMP search
Italy
• Napoli Univeristy “Federico II”
• LNGS – INFN
• Bari University
Japan
• Nagoya University
5
AgBr crystal size 0.2-0.3 mm
A long history, from the discovery of the Pion (1947) to the evidence of nm nt oscillation
in appearance mode (OPERA, 2014)
N. Di Marco
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
Moriond Cosmology - March 2014
Nuclear Emulsion
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Chemical composition
of nuclear emulsions
% 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
Br
Ag
N. Di Marco
A
O
N
C
Moriond Cosmology - March 2014
Nuclear Emulsion
Lighter nuclei
(longer range at same recoil energy)
↓
Sensitivity to low WIMP mass
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Moriond Cosmology - March 2014
Br
WIMP mass [GeV/c2]
WIMP velocity < 800 km/sec
Take e.g. MWIMP ~ 150 GeV/c2
Range [nm]
Ag
Recoil energy [keV]
N. Di Marco
Max recoil energy [keV]
Nuclear Emulsion
Br range < 300 nm
Recoil energy < 500 keV
8
OPERA emulsion films:
Silver grain size ̴ 200 nm  too large to record nanometric nuclear recoils
Natsume et al, NIM A575 (2007) 439
N. Di Marco
35 nm crystal 70 nm crystal 100 nm crystal 200 nm crystal
Moriond Cosmology - March 2014
NIT emulsion films: Nano Imaging Trackers
Recent developments
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Range distribution [nm]
(T. Naka et al., NIMA581 (2007) 761)
Chemical treatment
Expansion of
emulsion film
N. Di Marco
Film expansion technique
Moriond Cosmology - March 2014
Concept of readout: step 0
10
Film expansion technique
(T. Naka et al., NIMA581 (2007) 761)
Chemical treatment
Expansion of
emulsion film
Elliptical shape
Random noise
Circular shape
N. Di Marco
Signal track
Moriond Cosmology - March 2014
Concept of readout: step 0
10
N. Di Marco
Scanning with optical microscope and shape recognition analysis
Moriond Cosmology - March 2014
Concept of readout: step I
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
11
Test using 400 keV Kr ions
N. Di Marco
Scanning with optical microscope and shape recognition analysis
Moriond Cosmology - March 2014
Concept of readout: step I
12
Moriond Cosmology - March 2014
Concept of readout: step I
Scanning with optical microscope and shape recognition analysis
N. Di Marco
Test using 400 keV Kr ions
θ
Direction detected!
12
Nucl.Instrum.Meth. A680 (2012) 12-17
N. Di Marco
Scanning with X-ray microscope of preselected zones
Moriond Cosmology - March 2014
Concept of readout: step II
Pin-point check at X-ray microscope of candidate signals selected by optical readout.
Resolution ̴ 30 nm
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236nm
330nm
600nm
X-ray microscope
Optical microscope
486nm
N. Di Marco
Scanning with X-ray microscope of preselected zones
Moriond Cosmology - March 2014
Concept of readout: step II
14
236nm
330nm
600nm
X-ray microscope
Optical microscope
486nm
Matching of recoiled tracks
between Optical and X-ray
microscope
Success rate of matching
572/579=99%
N. Di Marco
Scanning with X-ray microscope of preselected zones
Moriond Cosmology - March 2014
Concept of readout: step II
14
Scanning with X-ray microscope of preselected zones
330nm
600nm
Success rate of matching
572/579=99%
N. Di Marco
236nm
X-ray microscope
Optical microscope
486nm
Matching of recoiled tracks
between Optical and X-ray
microscope
angular resolution [degrees]
optical microscope 31.4 +- 4.7 degree @original range: 150-250nm
X-ray microscope
16.8+-2.9 degree
Moriond Cosmology - March 2014
Concept of readout: step II
@original range: 150-250nm
14
NIT technology
Optical and X-ray read-out system
Intrinsic background measurement
Angular resolution measurement, neutron test beam
Full MC simulation
N. Di Marco
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Moriond Cosmology - March 2014
R&D activity
15
NIT technology
Optical and X-ray read-out system
Intrinsic background measurement
Angular resolution measurement, neutron test beam
Full MC simulation
N. Di Marco
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Moriond Cosmology - March 2014
R&D activity
15
Zero-background hypothesis
90% C.L.
100 nm tracking threshold
directionality information not included
N. Di Marco
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Moriond Cosmology - March 2014
Sensitivity
16
N. Di Marco
• 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
Moriond Cosmology - March 2014
Conclusions
• NIT (Nano Imaging Tracker)
• Read-out system based both on optical (200 nm resolution)
and X-ray microscopy (30 nm resolution)
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… from the R&D to the experiment in few years