The performance and status of directional dark matter search

with the nuclear emulsion2015/06/02

T. Asada

Nagoya University

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

2

topic

• Introduction

• Emulsion detection performance• theoretical performance• readout performance & calibration• ideal sensitivity

• background• electron BG• noise BG

• plan of underground experiment

3

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

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

• 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

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

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

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

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

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

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.

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

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

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

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

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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