the performance and status of directional dark matter search with the nuclear emulsion 2015/06/02 t....
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The performance and status of directional dark matter search
with the nuclear emulsion2015/06/02
T. Asada
Nagoya University
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Nagoya University T. Naka , T. Asada , T. Katsuragawa , M. Yoshimoto , A. Umemoto ,
S. Furuya , S. Machii , H. Ichiki , O. Sato , Y. Tawara
University of Napoli G. de Lellis , A. Di Crescenzo , A. Aleksandrov , V. Tioukov
University of Padova C. Sirignano
LNGS N. D’Ambrossio , N. Di Marco , F. Pupilli
Rome UniversityG. Rosa, P. Monacelli
Collaboration
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topic
• Introduction
• Emulsion detection performance• theoretical performance• readout performance & calibration• ideal sensitivity
• background• electron BG• noise BG
• plan of underground experiment
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Directional search with emulsion• Good scalability
• Solid state & good uniformity• Large scale production
• Self production ( ~ 10 kg / month)
• high scanning power• ~ g /day at current R&D, and many large scale experiments
• Good Angular resolution• ~ 20 deg (1 sigma) including scattering• DM direction sensitivity with equatorial telescope
cygnus Direction recognizingWIMP Fine crystal nuclear emulsion
NIT
atom Mass fraction %
H 1.63
C 10.12
O 7.40
N 2.68
S 0.03
Ag 44.07
Br 32.20
I 1.87
Light & heavy component
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The situation and strategy
MSSM region search: • AgBr targets are almost dominant• high energy deposit→high background rejection power will be expected• ton scale is required→difficult
DAMA region search:• scale is possible (~ 10 kg)• CNO targets are sensitive• CNO has relative low energy
deposit → background rejection study
Our First target should be DAMA region5
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detector performance
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Detection process of Emulsion
Intrinsic detection threshold is estimated about two times of crystal size (~ 40 nm)But the exact relativity between micro construction of crystal and detected track were not studied.→ realistic simulation with micro construction
electron-
Development
particle
Silver Bromide crystalin gelatin film
dissolved
Silver grainAg core
7
43 nm
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• We construct new simulation which calculate geometrical effect of each 1 crystal.
• Then we combine the simulation to SRIM.
→the intrinsic performance of particle detection
Intrinsic performance of Emulsion
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300 nm0 100 200
NIT (43nm)
imaginal crystal arrangement particle simulation by SRIM
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Carbon Energy [keV]
The result of Intrinsic tracking sensitivity
tracking efficiency (simulation) angular resolution (simulation)
Emulsion can detect a track with a order of keV as “track”.
→ How do we readout such low energy tracks?
XENON100 Leff (relative scintillation efficiency)
Aprile et al. (XENON100) PRD 88, 012006 (2013)
2 2
Carbon Energy [keV]
old estimationrange > 150 nm(Energy > 28keV)
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readout concept
Optical microscope
Scalability is OK, resolution is not enough
X-ray microscope
good resolutionscalability is not enough
486nm
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readout concept
486nm
Further analysis
The signals are unchanged and read any time
Combination of multi methods
Optical microscope
Scalability is OK, resolution is not enough
X-ray microscope
good resolutionscalability is not enough
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Optical readout system : trigger of signal
Napoli (Italy)
LNGS (Italy)Nagoya (Japan) 2nd unit
Nagoya (Japan) 1st unit
upgrade
new
new
New scanning machines (improved optical system, ~ g/day speed) are ready ! → calibration study is in progress
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X-ray microscope : confirmation
486nm
X-ray microscope etc.
Optical microscope
candidate selection
confirmation
SPring-8 @ Japan
8keV
X-r
ay
Zone plateZernike phase plate
X-ray microscope is already established technique
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Cal.1 : Optical readout efficiency
optical readout efficiency
Track Range (on X-ray) [nm]
Rat
e [O
ptic
al /
X-r
ay e
vent
]
Optical Track recognition efficiency
Optical selected events
X-ray all track events
=
Recognition threshold ~ 150 nmcurve function is available for exact efficiency 14
Optical readout use EllipticityWe associate it with track range
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emulsion film
ion direction
Cal.2 : Optical signal selection performance
11µm
Ion implantation system (Nagoya univ)gas source : Kr, Ar+CO2, N2, BF4 → Main target (C, N, O) are available acceleration voltage : 5 - 200keVmonochromatic energy parallel angle beam
contour fit• angle• ellipticity cut
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signal selection performance (Carbon)
At least, > 60 keV Carbon are detectableAngular resolution(1sigma) :~ 20 deg (60 - 100 keV)
Detail : Katsuragawa’s talk (tomorrow)
xy projected angle [rad]
Elli cut 1.25
Elli cut 1.40
Elli cut 1.60
Energy [keV]
Preliminary
Eff
icie
ncy
100 keV
60 keV
signal selection efficiency
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0 20 40 60 80 1000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
tracking detection efficiency
track readout measured
energy [keV]
effi
cien
cy
Comparison between simulation (intrinsic)
and calibration (readout)
0 20 40 60 80 1000
0.1
0.2
0.3
0.4
0.5
0.6
signal angular resolution
SRIM trackreadout measured
energy [keV]an
gula
r di
stri
buti
on 1
σ [
rad]
cal.1 cal.2
the simulation result is consistent with calibration dataangular resolution of readout system is smaller than error
― SRIM estimation ― new simulation― efficiency calibrated simulation ― optical calibration data
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scattering
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Correction of scattering effect
z
yxion
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range [nm]
total detectedusual eventreflected event
DM situation
ion implantation
0 20 40 60 80 1000
0.10.20.30.40.50.60.70.80.91
energy [keV]
effici
ency
0 20 40 60 80 1000
0.10.20.30.40.50.60.70.80.91
energy [keV]
effici
ency
10 ~ 20 % improve
Spectrum of calibration data is distorted. Correct spectrum should be used for DM calculation
100 keV Carbon
some events go outside
tracking detection efficiency
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The experiment performance
• the calibration result in 60~100 keV Carbon is consistent with simulation
extrapolate the simulation to other energy, nuclei
↓
estimation of experiment performance
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Ideal sensitivity of experiment
preliminary
In the ideal condition, we can cover DAMA region with simply scale-up experiment.
the error of non-calibrated regions(a order of keV) cause strong effect to the performance, so further calibration study is necessary.
― --- Cut 1.6― --- Cut 1.4― --- Cut 1.25■■ DAMA
Cross Section Limit (0 BG 25 kg ・ year 90%CL)
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Background
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background study status
• The detection performance was determined
next step• background sensitivity• rejection study
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228Ra, 40K (0.4 – 6.2) × 104 /kg/day 110Ag 2.5 × 105 /kg/day14C 1.7 × 106 /kg/day (NA)
Ge spectroscopy in LNGS (Italy) Type gelatin AgBr crystal
electron background
106 rejection power for electrons is required23
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Background rejection- cryostat chamber -
B. Maglic et al, Phys. Rev. 123.1444 (1961)
temperature dependence of emulsion sensitivity (not NIT)
Sample # grains / 1000 mm3
Exposed at 300 K 43 4
Exposed at 83 K 0.19 0.02
Unexposed at 300 K 0.25 0.03
*g–electron developing possibilityupper limit : < 2×10-3 (90% C.L.)
BG sensitivity is controllable !
preliminary result
241Am γ-ray sensitivity
room & LN2 temperature
pumped down to 0.02 atm
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Background rejection - chemical treatment -
2,3-di(methoxyphenyl)-5-phenyltetrazolium
Tetrazolium-compoundsnew chemical treatment for electron rejection
preliminary test result
1. high electron rejection power• electron developing possibility
→ < 3×10-3 (90 % C.L.)
⇒we can expect the background rejection power with readout more than > 106
2. High detection efficiency 30 keV C ions → 100 % consistent
high S / low N will be possible!
We can use use it by just mixing to gel
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These are just intrinsic efficiency.The more rejection power will be achieved with readout selection.combine them, we plan 106 rejection.
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noise from other origin
― : alpha― : non-exposed
mean brightness
α-rays elements
mean brightness
Generated by Development
― : developed ― : non-developed → dusts
10um
alpha-ray
noise
(same to non-exposed)
signal / noise noise typebrightness comparison on analysis
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Kind of events source
• Signal event (recoiled nuclei)• de/dx : 100~1000 keV/um• Cores become strong(big) and many
• Background event (electron)• de/dx : 1~10 keV/um• Cores become small and few
• Noise event (not from particle, unknown)• Core may be bigger than signal’s one.
hole+ electron-
?
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Kind of events source
The difference may appear in detail of readout signals
→plasmon analysis (Umemoto’s talk, 3rd day)
non-tracking rejection will be possible !
hole+ electron-
? ?
developing
after developing
Y a
xis
Y a
xis
X axisX axis
Y a
xis
plasmon analysis
58 nm58 nm
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neutron background
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Nuclear recoil induced by neutrons( > 100 nm tracks)
⇒ 0.065/kg/y
neutron from OutsideStudies of the flux measurement and shielding plan are in progress
Neutron from inside
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plan of underground experiment
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experiment design
Hall B
preparation for underground exposure
required underground facility Detector production facility
• film production (pouring)• underground gel production
clean room dev room shield equatorial telescope
the plan will submit to LNGS committee on this month. 31
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Production system (Nagoya, Japan)R&D machine
Scale: 200 g/daySemi mass production machine
Scale: 600 g/day→Production ability
~ 10 kg / month
Production of Emulsion
Stable & enough emulsion production is already possible
projects for underground run :• film construction in underground• emulsion production in underground
100nm32
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Experimental set-up: a possible design
Passive shielding
Radon box
Equatorial Telescope NIT sample
PE50 cm
Pb20 cm
Cu14 cm
Plexiglass
3 m
2 m
all elements put inside the shield
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Other case of design
the case that equatorial telescope become serious BG source
→ put on the equatorial telescope
• several ton pay load is easy
• compatible with cryostat ?
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schedule2016
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2017 2019
scale up study
equatorial telescope
plasmon analysis study
mini-run for BG measurement
signal calibrationBG calibration
large scale run
shield construction
long term stability
detector production facility
readout upgrade
S/N improve study
Understanding of the detector large scale run
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summary
• We aim to search DAMA region with CNO detection and good BG rejection experiment.
• Detector calibration started. It shows good angular resolution (~20˚) and lower energy sensitivity (< 60 keV).
• New detector simulation are in good agreement with the experimental data.
• BG measurement and rejection study started. We try to archive 106 rejection power combination with detector intrinsic and readout technique.
• Underground experiment was scheduled. We will begin mini-scale run soon, and plan to start large scale in 2019.
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End
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