1. 2015/06/02 T. Asada Nagoya University
The performance and status of directional dark matter search with the nuclear emulsion
2015/06/02
T. Asada
Nagoya University

2. Collaboration 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 University
G. Rosa, P. Monacelli
Japanese people are mainly take charge of detector study, and Italian people are take charge of underground experiment design.
readout system are developed both on Japan and Italy in parallel

3. topic Introduction Emulsion detection performance background
theoretical performance
readout performance & calibration
ideal sensitivity
background
electron BG
noise BG
plan of underground experiment

4. Directional search with emulsion
Light & heavy component
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
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
cygnus
WIMP
Fine crystal nuclear emulsion
NIT
Direction recognizing

5. 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
Minimal Supersymmetric Standard Model
Our First target should be DAMA region

6. detector performance

7. Detection process of Emulsion
particle
43 nm
Silver grain
Ag core
Development
electron-
dissolved
Silver Bromide crystal
in gelatin film
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

8. Intrinsic performance of Emulsion
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
300 nm
100
200
NIT (43nm)
imaginal crystal arrangement
particle simulation by SRIM

9. The result of Intrinsic tracking sensitivity
tracking efficiency (simulation)
angular resolution (simulation)
old estimation
range > 150 nm
(Energy > 28keV) 2 2
Carbon Energy [keV]
Carbon Energy [keV]
XENON100 Leff (relative scintillation efficiency)
efficiency: previous is just cut the threshold, but new simulation gives the curve as a function of energy.
efficiency curve of Xenon 100 experiment
angle : such low energy can be detect as “track”. scattering is dominant
Efficiency curve of XENON 100 experiment. they have sensitivity until several keV, but the efficiency is not so high.
Emulsion can serch near region in theory.
Emulsion can detect a track with a order of keV as “track”.
→ How do we readout such low energy tracks?
Aprile et al. (XENON100)
PRD 88, (2013)

10. readout concept Optical microscope X-ray microscope
Scalability is OK, resolution is not enough
486nm
lined silver grain can be seen as …
fuzzy picture
clear picture
X-ray microscope
good resolution
scalability is not enough

11. readout concept Combination of multi methods Optical microscope
The signals are unchanged and read any time
Optical microscope
Scalability is OK, resolution is not enough
486nm
X-ray microscope
good resolution
scalability is not enough
Further analysis

12. Optical readout system : trigger of signal
Nagoya (Japan) 1st unit
Napoli (Italy)
new
LNGS (Italy)
new
Nagoya (Japan) 2nd unit
upgrade
Introduction of Optical readout system.
We had used left up machine, but recently we constructed new machines.
New scanning machines (improved optical system, ~ g/day speed)
are ready ! → calibration study is in progress

13. X-ray microscope : confirmation
Optical microscope
candidate selection
Japan
confirmation
486nm
8keV X-ray
Zone plate
Zernike phase plate
X-ray microscope etc.
X-ray microscope is already established technique

14. Cal.1 : Optical readout efficiency
Optical readout use Ellipticity
We associate it with track range
optical readout efficiency
Track Range (on X-ray) [nm]
Rate [Optical / X-ray event]
Optical Track recognition efficiency
Optical selected events
X-ray all track events =
Recognition threshold ~ 150 nm
curve function is available for exact efficiency

15. Cal.2 : Optical signal selection performance
ion direction
emulsion film
11µm
Ion implantation system (Nagoya univ)
gas source : Kr, Ar+CO2, N2, BF4
→ Main target (C, N, O) are available
acceleration voltage : keV
monochromatic energy
parallel angle beam
contour fit
angle
ellipticity cut 15

16. signal selection performance (Carbon)
signal selection efficiency
Elli cut 1.25
Elli cut 1.40
Elli cut 1.60
Energy [keV]
Preliminary
Efficiency
xy projected angle [rad]
100 keV
result of calibration
signal selection efficiency depends on energy
color means signal selection cut
in typical cut, we can detect 60 keV signals as directional tracks
60 keV
At least, > 60 keV Carbon are detectable
Angular resolution(1sigma) :~ 20 deg ( keV)
Detail : Katsuragawa’s talk (tomorrow)

17. Comparison between simulation (intrinsic) and calibration (readout)
scattering
red line is simulation data
calibration 1 ; optical readout efficiency is applied to simulation data, drawn by blue line.
and calibration 2 ; data of ion implantation calibration is drawn by green line.
black line of angular resolution is SRIM data of scattering.
see blue and green line.
― SRIM estimation ― new simulation
― efficiency calibrated simulation ― optical calibration data
the simulation result is consistent with calibration data
angular resolution of readout system is smaller than error

18. Correction of scattering effect
tracking detection efficiency
ion implantation
total detected
usual event
reflected event
ion z y x
some events
go outside
range [nm]
DM situation
10 ~ 20 % improve
100 keV
Carbon
green line is scattered event. reflected means that the end point of track is outside of emulsion.
red line events are stopped inside emulsion.
With this correction, the efficiency will be improve about from 10 to 20 % in DM event situation.
Spectrum of calibration data is distorted.
Correct spectrum should be used for DM calculation

19. 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

20. Ideal sensitivity of experiment
Cross Section Limit (0 BG 25 kg・year 90%CL)
― --- Cut 1.6
― --- Cut 1.4
― --- Cut 1.25
■■ DAMA
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.
preliminary

21. Background

22. background study status
The detection performance was determined
next step
background sensitivity
rejection study

23. electron background 106 rejection power for electrons is required
Ge spectroscopy in LNGS (Italy)
Type gelatin AgBr crystal
some atom is not mBq, Bq
please see the 110mAg, it is dominant of all atom.
In addition it, gelatin include carbons, so natural abundance of 14C should be large population. These two are dominant electron background.
228Ra, 40K (0.4 – 6.2) × 104 /kg/day
110Ag 2.5 × 105 /kg/day
14C × 106 /kg/day (NA)
106 rejection power
for electrons is required

24. Background rejection - cryostat chamber -
temperature dependence
of emulsion sensitivity (not NIT)
241Am γ-ray sensitivity
room & LN2 temperature
pumped down to 0.02 atm
preliminary result
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
This is one candidate of electro rejection.
Emulsion detection sensitivity usually have temperature dependence.
This result is first test of the dependence of fine crystal emulsion.
*g–electron developing possibility
upper limit : < 2×10-3 (90% C.L.)
BG sensitivity is controllable !
B. Maglic et al, Phys. Rev (1961)

25. Background rejection - chemical treatment -
Tetrazolium-compounds
new chemical treatment for electron rejection
preliminary test result
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!
2,3-di(methoxyphenyl)
-5-phenyltetrazolium
We can use use it by just mixing to gel
This is another solution of electron rejection.
the concept is direct control of each crystal sensitivity.
These are just intrinsic efficiency.
The more rejection power will be achieved with readout selection.
combine them, we plan 106 rejection.

26. noise from other origin
10um
alpha-ray
noise
brightness comparison on analysis
mean brightness
α-rays elements
signal / noise
noise type
Generated by Development
blue event is not particle source, not dusts, the origin is unknown.
― : alpha
― : non-exposed
― : developed
― : non-developed
(same to non-exposed)
→ dusts
mean brightness

27. Kind of events source Signal event (recoiled nuclei)
hole+ electron-
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. ?

28. Kind of events source after developing
hole+ electron-
The difference may appear in detail of readout signals →plasmon analysis (Umemoto’s talk, 3rd day) non-tracking rejection will be possible !
developing
plasmon analysis
X axis
Y axis
Y axis
X axis
58 nm
58 nm ? ?

29. Nuclear recoil induced by neutrons
neutron background
Neutron from inside
Nuclear recoil induced by neutrons
( > 100 nm tracks)
⇒ 0.065/kg/y
neutron from Outside
Studies of the flux measurement and shielding plan are in progress

30. plan of underground experiment

31. experiment design
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.
Hall B

32. Production of Emulsion
Production system (Nagoya, Japan)
R&D machine
Scale: 200 g/day
Semi mass production machine
Scale: 600 g/day
→Production ability
~ 10 kg / month
Stable & enough emulsion production is
already possible
projects for underground run :
film construction in underground
emulsion production in underground
100nm

33. Experimental set-up: a possible design
Passive shielding PE
50 cm
Radon box
Plexiglass
Equatorial Telescope
NIT sample Cu
14 cm
2 m Pb
20 cm
3 m
all elements put inside the shield

34. 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 ?

35. schedule signal calibration BG calibration readout upgrade
2019
2016
2017
Understanding of the detector
scale up study
large scale run
signal calibration
BG calibration
readout upgrade
S/N improve study
long term stability
detector production facility
plasmon analysis study
equatorial telescope
shield construction
mini-run for
BG measurement
large scale run

36. 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.

37. End