液体アルゴンによる

Non-WIMP暗黒物質探索に関する考察
早稲田大学 (ANKOK Group)
木村 眞人

ダークマターの懇談会2020 | 2020.09.08 @ ZOOMLAr vs LXe2

液体キセノン

液体アルゴン

原子番号

54

18

低質量WIMPに対して大きな反跳エネルギー

沸点

165 K

87 K

高純度化が容易

密度

3.0 g/cm3

1.4 g/cm3

W値

14.7 eV19.5 eV

蛍光波長

175 nm

128 nm

蛍光時定数 (早)

4 ns

6 ns

蛍光時定数 (遅)22 ns

1.6 μs

長寿命RIなし

39Ar (269yr)

価格~500,000円/kg(~1,000円/kg)▲ 自己遮蔽力

同程度の観測光量・電子量を確立▲ 直接検出の困難

波長変換技術の確立，新デバイス開発

非常に優れた粒子識別能力(電場の有無によらない)▲ 極めて厄介な電子反跳背景事象源

精製・除去技術の開発

大気アルゴンであれば容易に入手可能

LAr Scintillation Detector3

液体アルゴン中のシンチレーション光(S1)と，電離電子が誘発するエレクトロルミネセンス光(S2)を検出

Photo-devices- 低エネルギー (数光子 or 1電子信号) 事象に有感

S2Extraction
Grid
LiquidArgone- e- e

Pa

rt

ic
l

es

S1

~1 kV/cm

Gas
Argon

>3 kV/cm

Lightguide- 3次元位置再構成能力 (光検出パターン

S1-S2時間差)- 電子反跳(β/γ)と原子核反跳(中性子/WIMP/(α))の識別: S1波形弁別 (PSD)

電離蛍光比 (S2/S1)

粒子識別

発光過程

1 +
+
3
Σu or Σu

液体アルゴン分子の励起状態はdE/dxやエネルギー損失量に強く依存(スピン一重項 or スピン三重項)

2つの励起状態で崩壊時定数は>100倍異なる
シンチレーション光波形による非常に優れた事象弁別

5 keVee- 電場の有無に関わらず機能

電子反跳- 分離能力は観測光量に比例して向上- 非物理的な事象も効率的に除去- Standard-WIMP探索の強力な武器 (対39Ar)
電子反跳信号の探索に対しては別のアプローチを採らなければならない → 次頁

原子核反跳

4

Rb of ð33.1 " 0.9Þ events=d in agreement with thevalue ð35.3 " 2.2Þ events=d obtained from the known
5
branching ratio and the spectral fit result. The presence

背景事象源

PRD 93, 081101(R)大気アルゴン

最大の電子反跳背景事象源：39Ar

2

1/1400x- Cosmogenic: (40K + e- => 40Ar + νe + γ),
40Ar(n, 2n)39Ar, 40Ar(μ,d)39Cl, etc.

地下アルゴン- t1/2 = 269 yr,

Argon Extraction-Cortez, Colorado- Qβ = 565 keV

Argon on Earth- 通常 (大気アルゴン中)，1
Bq/kgで存在
Atmospheric isotopic abundanceApproximate Input:

269 y36Ar – 0.334%

Qβ−=565

38Ar – 0.063%

40Ar – 99.604%

40

0

39
≈ 18Ar

100%

40

10.11

3/2+

39
19K

0

stable- 地下ガス田のCO2中のアルゴンを抽出
Underground via U + Th fission neutrons(CO2中に400 ppm)
39Ar Origins

40Ar(n,2n)à39Ar
40Ar(p,np)à39Ar- 精製実績 = 140 g/day

2

2

4

Zeolite column“Depleted Argon” (by DarkSide-50): 39Ar = 0.7 mBq/kg
Ar comes from K decay
J.-Y. Lee, et al., Geochim. Cosmochim. Acta 70 (2006) 4507-4512

7/2–

Gas Type
Concentrationin Output
FIG. 1. Live-time normalized S1 pulse integral
spectrafromHelium
85-95%
Argon
3-6%
flows
Simultaneously
single-scatter Gas
eventsinAAr(black)andUAr(blue)
taken
Nitrogen
1-10% withthrough one
the other column
Trace 39
85 Methane, Oxygencolumn underis pumped on to
200 V=cm drift
field.
Also shownremove
arethe the Kr(green)andAr
CarbonDioxideTracepressure.
CO ,Other Hydrocarbons
Trace
H O and CH
trapped gases(orange) levels
as inferred from a MC fit. NotetheProduction:
peak intheare adsorbed
Average
140g/dayon zeolite
lowest bin of the UAr spectrum, which is due to 37 Ar from
MantleLow U and Th
cosmic-ray
activation. The peak at ∼600 PE is due to γ-ray(lowest Ar)
Adsorbed gas
Compton backscatters.
Gas from

Concentration from well
96%
2.4%
0.57%
0.43%
0.21%
440 ppm

Zeolite column

Gas Type
Carbon Dioxide
Nitrogen
MethaneHeliumOther hydrocarbons
Argon

He, Ar, N2
mixture39

well

Thomas Alexander(@LRUA Workshop 2018)

returned tocompany

F
c
p
c
th
sc
n

081101-

for N e− ≳ 7 e ð∼1 keVNR Þ. There is an excess of data in− to 7 e− , the origin of which is−theregion
of
N
from
4
e
e
Argon : DarkSide-50 (PRL
121 081307)
left for future
study.
Xenon : XENON1T(PRL
123 251801)

Upper limits on the WIMP-nucleon scattering crosssection are extracted from the observed N e− spectrum
using a binned profile likelihood method [56–58]. Two 6
signal regions are defined, the first one using a threshold of
4 e− , determined by the approximate end of the trappedelectron background spectrum, and the second above a−thresholdof7e, where the background is described
PHYSICAL REVIEW LETTERS 123, 251801 (2019)within uncertainties by the G4DS simulation. The firstregion has sensitivity to the entire range of DM masses
as the trigger preselects S2’s to which many PMTs
explored in this Letter, but the data are contaminated by acontribute, which is rarer for S2’s seen mostly by thecomponent that is not included in the backgroundmodel,
top array.
1 event
resulting in weaker bounds on the DM-nucleon crossPileup of randomly emitted single-electron (SE) signals/[kg day keV]
can be misidentified as S2’s from real events. We employ
section. The second signal region has limited sensitivity
three cuts against this background, without which theto DM masses below 3.5 GeV=c2 but, due to the agreement
population most prominent at ≲150 PE in Fig. 3 would
between data and background model, more
tightly con~3桁
be ∼50× larger. First, we remove events whose S2 hit
strains the cross section at higher masses. For a given
3 energy
keV
patternon DarkSide-50
the top array Nise−inconsistent
with
that
of single
eeFIG.
7. Thespectra at low
recoilfromfluctuation model and DM mass, we calculate limits using
a likelihood
test compared[15]. This with
cut a
the scatters,
analysis asof determined
the last 500bydays
of exposure
both signal regions and quote the more stringent of the two.
has simulation
a 90% efficiency,
shown in components
brown in Fig.
as
G4DSof the backgroundfrom2,known
The 90% C.L. exclusion curves for the binomial flucmeasuredcontaminants.
with neutronAlso
generator
datatheandS1-tagged
radioactive
shown
are
spectraexpected
Depleted-Argonを用いた場合でも，
tuationmodel(reddotted
line)
and
the
model
with
zero
events. byThis
also particles
removes ofsome
unresolved
for cathoderecoils induced
darkcutmatter
masses2.5, 5, andfluctuationintheenergyquenching(reddashedline)
are2 scatter events, e.g., from radiogenic neutrons.
−40
2
double
10
GeV=c
with
a
cross
sectionpernucleonof
10cm
LAr検出器の事象レートは約3桁高い
3keV
ee 2 , the
shown
in
Fig.
8.
For
masses
above
1.8
GeV=c
Second, with
we exclude
events with
one orfluctuation
more S2 modelor
convolved
the no energy
quenching
FIG.
4.
Distributionofevents
that
pass
all
cuts
(blackdots);
90%
C.L.
exclusionisnearlyinsensitive
tothechoice ofsingle-electron
signalsup
to∼1
ms
beforethelargestand detector resolution. The y-axis scales on the right-hand side
2, the two- 原子番号の小ささ(i.e.反跳エネルギーの大きさ)
に帰して，
error
bars
show
statisticaluncertainties(1σ
Poisson).
The
thick
−
quenchingfluctuation
model.
Below
1.8
GeV=c
with 91.5%
efficiency,
as measured
are S2,
approximate
event
rates normalized
at Nwith
10 e .
e− ¼high-energy
black line shows the predetermined summed background model,
background events and shown in orange in Fig. 2. This2cut
below which its three components are indicated, with colors as in
Low-Mass
WIMP(1.8‒3.5
GeV/c)に対してはより高い感度を持っている
also suppresses gas events, whose S1’s are broader thanFig. 3. The lightly shaded orange (purple) histogram, stacked on
081307-6
those of events in the liquid and therefore often misidenti2
the
total
background,
shows
the
signal
model
for
4
GeV=c
fied as S2’s. Third, as high-energy events cause a temporary 39Arの除去が不可欠
電子反跳稀信号の探索には，さらなる(20 GeV=c2 ) SI DM models excluded at exactly 90% confidence
and localized enhancement in single-electron emission
level. The arrows show the ROIs for these analyses, and theLAr vs LXe(≤3 keVee)
Xenon

Argon

背景事象源7

Depleted-Ar

h2

39

Events/(t⋅y⋅keV)

Xe1Tの背景事象レベルを得るには，39Arを大気アルゴンから10-5~-6の抑制が必要- これまでの達成値から1/100x ~ 1/1000x- (アクシオン信号であればさらに1/10x)- O(1t-10t)の生成量も必要

1/10x

104

Ar (0.7143 mBq/kg)

39

Ar (0.0714 mBq/kg)

39

Ar (0.0007 mBq/kg)

Xenon1T
ABC axion

3

10

1/100xPrimakoff axion
57

Fe axion

102

Axion Signal :Xe1Tのベンチマーク

05

Production
and Purification
Depleted Argonの大量生成 (byDarkSide)

10
Energy (keV)

15

20

Production and Purification
新蒸留塔

Preliminary lay-out- 精製施設を増強 (250 kg/day，建設中)- 蒸留塔 (350m) による追精製・追純化(~10 kg/day，コミッショニング中?)✦ 計画通り稼働開始すれば，

新精製施設
Preliminary lay-out

UAr transported via boat
for final purification at Aria

Production: Urania• Commercial-scale plant to a^er
extract
POLARISUAr
Srl• Located in Southwestern Colorado• UAr extracted from CO2 well gas at the tonne scale

1tonの39Ar-Freeアルゴンも得られるはず

UAr transported via boat
for final purification at Aria
Andrew Renshaw (@LRUA Workshop 2018)

57

126.1

Co

0.97

+0.003−0.003—

低エネルギー信号と応答

PRD 87, 115015

1- 生成光子数/電子数の詳細な測定- 種々の実験グループによる測定と，

0.6
0.4
0.2

“NEST”をはじめとした包括的なモデル化

0Compton scatters (this work)
Calibration sources (this work)
Band used for threshold calculation

0.5

1

2

5

10

20

Energy [keV]

50

100

- 低エネルギー電子反跳に対する検出器応答の理解・解析に大きな貢献

液体アルゴンの理解はまだまだ乏しい——

0.593+0.003+0.009−0.003−0.009

8where δA is the uncertainty in the so2(as in Eq. (5)) and σA
is the variance o
2fit. The factor cov(LY0 , A)/σA
gives
LY0 versus A.

• σ (4) quantifies the uncertainty associachoice of 6
theP10002
PMT coincidence requi
JINST
N = 2 coincidence requirement on t
PMTs is separately imposed, correctin
ing scintillation spectrum by a simu
dence efficiency curve, and performingfor LY0 .

0.8

Re

液体キセノン応答理解の目覚ましい進展

Obodovskii (1994)
Aprile (2012)
NEST (v0.98, 2013)—

200• σ (5) is a 1.5% relative systematic fromin the PMT gains and weekly 57 Co ca

These systematic uncertainties are combine
ture to form the systematic error bars in F
the first four are shown in Table I. In the lo
the dominating systematic is σ (4) with a co38%; this systematic rapidly decreases to 1%
zero beyond.

FIG. 7: (color online) Results of the light yield relative tothat of the 32.1 keV emission of 83m Kr, Re . The current
work (red) shows statistical uncertainties as vertical lines, systematic uncertainties as light, shaded rectangles, and the 1 σ
spread in the distribution of electron recoil energies as horiD. Field dependence
zontal lines. Also shown are the results from studies with Xrays [35] (blue), the recent Compton-scatter study by Aprile
et al. [14] (purple) and the model predictionof NEST [36, 37]
previous
results
all pertain
theen- lFigure 5. Experimental values for absoluteTheS1 yields
for ER in xenon
as a functionof incident to
gamma(green). The gray band indicates the 1σ
ofwithReourmodels
ergyrange
comparedMonte Carlo output,
foundationof which is therecombination
probability
curve
LXethewith
no applied
electric
fields.
As ment
used to determine the energy thresholds
of fourrecentLXe
in figure
2. Fitted
Gaussianmeans (seetion
figure II,3, left)
are used
to report
the simulated
scintillation
data
were
also
collected
withyields.
andark-matter searches.
Data are taken from [3, 11, 17, 22, 26, 28, 33, 37–40]. When authors quote relative yields, we infer absolute- 液体希ガス検出器応答としての液体キセノンとの類似性

γ

e-

Xe/Ar

- 原子番号 (電子殻構造) の大きな差異→ “電子反跳”応答はよりシンプルだと期待γ

of 450 V/cm for a subset of scattering angle

numbers of photons, based on works where absolute yields are available (table 1). The 122 keV data havethe scintillationquenching
LXebeen separated for clarity. For these andstudy
other overlapping
points, some error
bars are thickerof
thanothersatfort
differentiation. Two points, at 164 and ergies.
236 keV (hollow
crosses[38]), are frominelastic
The bluedatacollected
withthisneutron
fieldscatareters, resulting in gammas of these energies together with an NR component, which may serve to increase thesame procedure as before, resulting in a set
yield. The right-hand y-axis uses the definition Wph = Edep /N ph , as described in the text. More features andsignificant outliers are addressed in section 3, where the work of Doke et al. [41], which is in good agreementwith our own, is also explained in depth. Following only the Doke/Birks or the Thomas-Imel model does notmatch the data at all energies. We isolate these models by setting the cross-over distance between the two to
be zero (dotted red) or infinity (dashed blue), implying only single boundless Thomas-Imel interaction sites
in the latter case. Multiple interaction sites are treated individually for determining which individual model
to use, thus the black curve for the full, combined model is not a simple average of the red and blue curves.

Xe/Ar

e-

X-ray
β-likeCascade, larger
dE/dx
–9–

低エネルギー事象のための検出器技術
3ʼʼ PMT9

真空紫外光 (128 nm) の高効率検出 @ 極低温- 光検出器窓面や検出器内壁 (反射材) へ
波長変換材 (TPB) を真空蒸着

LAr- 13 p.e./keV (PMT), ~25 p.e./keV (MPPC)
を実証 (c.f. XMASS ~ 15 p.e./keV)
電離電子生成量の向上と電離信号検出効率の最大化

高電圧印加回路

LAr- 電離電子検出効率~100%- S2増幅率>10 photon/e-

Pulse Height (a.u.)- 高ドリフト電場の形成 (最大3 kV/cm)
5
ANKOK
4

S2

高

電

3

場

22

Na Data
E = 0.2 kV/cm
E = 0.5 kV/cm
E = 1.0 kV/cm
E = 2.0 kV/cm
E = 3.0 kV/cm

2
1
0
− 20

S1
0

20

40

60

80

100

120
Time (µs)

低エネルギー応答の理解 @早稲田

10

高感度アルゴン検出器による低エネルギー応答測定- 光量に特化した1相検出器 (電場なし) により，10keV以下のシンチレーション応答を初めて測定- エネルギー依存性を関数化

Scint. Eff. (Referenced to 37Ar)

1.4

1.3
1.2

Uncertainty

1.1

Litelatures (Normalized at 511 keV)1

Qy (e /keV)

0­3 kV/cm下での検出器応答

DarkSide-10(AstropartPhys 49 44)

ARIS (γ -ray)(PRD 97 112005)

ARIS (Compt.Electron)(PRD 97 112005)

arXiv:2003.14248(arXiv:1909.02207)

103

102
Energy (keV)

1

ER, 3000V/cm
30
20
10

NR, 3000V/cm

3
2

NR, 200V/cm(S1や電離電子生成量) を算出- 任意の電場下での電離電子生成量を予測- 1kV/cm以上での電子反跳応答の初めての測定

CLEAN(PRC 81 045803)

0.9 M.Kimura et al.,Xiong et al.

h-- 高電場印加に特化した2相型検出器により，(as a func. of ER Energy)

Best Fit (ς = 0.07)

0.8
Chapter 8 Conclusion and
1 Prospects 10

高電場アルゴン検出器による電場応答の測定

Pure-TIB (ς = 0.07)

Data (This work)

1
−1

5×10

~3x ER, 200V/cm

鷲見D論 (2018,早大)

10−12×10−1

1

2 34

10

20

102

Recoil Energy (keV)which had been used for the background predictions, andabundance, dark matter has not yet been directly
detected in terrestrial experiments. Many theoretical models predict particles with appropriate pherunning the analysis code applying all cuts to it. Figure 11
nomenological properties, such as those describedin [2, 3]. One such candidate is the weakly intershows f 90 vs S1 after all analysis cuts. With the analysis
acting massive particle (WIMP). In such models,the elastic scattering of WIMPs with nuclei produces
cuts applied and the data fully unblinded, no events are
low energy (.100 keV) nuclear recoils (NRs) [4]. Direct detection experiments seek to observe this sigobserved in the predefined DM search region.
nature; current results limit the spin-independent
WIMP-nucleon scattering cross section to be less
After unblinding, we tabulated events surviving each cut,than 9.0 ⇥ 10
cm at 100 GeV/c at 90% C. L. [5].
Detecting these rare, low energy signals is facilitatedby a large target mass with exceptionally low
as shown in Table V. The order that the cuts were applied isbackgrounds, below 1 event per tonne per year. PreStandard-WIMP探索
vious experimental results demonstrated the e↵ecnot meaningful—the order shown in the table was chosen
tiveness of liquid argon (LAr) for achieving these
conditions [6, 7]. Ease of purification, high scintilto be informative. Each of the last two events in Table V
lation efficiency and transparency to its own scintillation light makes it well-suited for a multi-tonne- bothDEAP3600(1相)，DarkSide-50
FIG. 13. (2相)Distribution
eventsin usesthe f 90 vs S1 plane thatwas cut by
the prompt and delayed
veto cuts. They are
WIMP detector. The of
DEAP-3600
experiment
the unique scintillation time profile of LAr to achieve
DEAPsurvive
allanalysiscuts andthat
survive tightened
pulse shape discrimination(PSD)[8]. Itin
has addition
prethe events in the box in Fig. 6 labeled “Radiogenic” andviously been shown that PSD can be used to sup2
radialand
S2/S1
cutsrecoil(seeforby details).
S1波形弁別によって >20 GeV/c の領域を
press electronic(ER) text
backgrounds
a factor
3600“Fission -candidate.”better than 2.7 ⇥ 10 , in an energy range of 44–

LArによるDM探索
47

Background-Freeに探索

2

The digitize
window, beg
enough to indrift time ofdigitized at 1of ∼0.25 PE
beginning 1

11

2

8

89 keVee [9].
The results presented here are from the
DEAP-3600 experiment, using non-blinded datacollected from November 4, 2016 to October 31,
2017. DEAP-3600 has previously performed thefirst WIMP search with a single-phase LAr detector (measuring scintillation only), during a
14.8 tonne·day total exposure [6]. In this paper, theresults are updated to a 758 tonne·day total exposure collected during 231 live-days. The result is themost sensitive dark matter search performed usinga LAr target for WIMP masses above 30 GeV/c2 .
This analysis shows the strongest background discrimination using PSD in any dark matter search, at9
the level of 4.1+2.1
for 90 % NR acceptance
1.0 ⇥ 10in the dark matter search region of 15.6–32.9 keVee .

Low-levesteps describthat make up
code based
art framewo≳10 PE in
DarkSideinformation
50 finding is donly integra
FIG. 1. Cross section of the DEAP-3600 detector components located inside the water tank (notFIG.
shown).1.Insidedescribed in
The DarkSide-50 TPC. Reproduced from [4] under [6].

VIII. WIMP SENSITIVITY AND LIMIT

Low-Mass
WIMP/Non-WIMP探索
A limit on spin-independent DM-nucleon scattering isderived assuming the standard isothermal WIMP halo
DarkSide-50
(2相,
200
V/cm)
model, with vescape ¼ 544 km=sec [42], v0 ¼ 220 km= sec[42], vEarth ¼ 232 km= sec [43], and ρDM ¼ 0.3 GeV=
S2のみを利用し，
2
3
ðc cm Þ [44]. The background- and signal-free result is
26
consistent with up to 2.3 DM-induced scatters (90% C.L.),
PHYSICALREVIEW LETTERS 12
0.6
keV
,
0.05
keV
閾値による探索nreewhich sets an upper limit ongroundthe spin-independent
DMexpectation of <1 event has been achieved;
the steel shell are inward-looking PMTs, light guides,
filler blocks, and the acrylic vessel (AV), which holds
the liquid argon target and the gaseous argon layer. Located on the outer surface of the steel shell are muon
veto PMTs. Above this, a steel neck contains the neckof the AV, acrylic flowguides and the cooling coil. The
neck is coupled to a central support assembly on which
the glovebox is located. Shown also is the neck veto fiber
system (green).

This value of the total LAr mass is calculated using
the same method as described in [6].

A.

II.

DETECTOR AND DATA ACQUISITION

PRD 100 022004

The DEAP-3600 detector is located approximately 2 km (6 km water-equivalent) undergroundat the SNOLAB facility near Sudbury, Ontario,
Canada. In the current run, the detector has been
operating with a LAr target since November 4, 2016.
The analysis of data from a previous run is discussed
in [6]. For the data collection period discussed here,
the total mass of the LAr target is (3279 ± 96) kg.

102006-3

Detector description

A cross-sectional diagram of the DEAP-3600 detector is shown in Figure 1. The complete design ofthe detector is detailed in [10]. The detector consists of ultra-pure LAr contained in a 5 cm thick ultraviolet absorbing (UVA) acrylic vessel (AV). ThisUVA acrylic was chosen to reduce the amount ofCherenkov light originating from the acrylic. The
top 30 cm of the AV is filled with gaseous argon(GAr). The GAr/LAr interface is 55 cm above theequator of the AV. The GAr and LAr regions are*−44
2
nucleon cross section
at
1.14
×
10
cm
(3.78
×
Co
this model is consistent with observations in data
7)
1
0
(2
−44
2
−43
2 in the ROI. Multivariate
2
2
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PRL 121 081307
ACKNOWLEDGMENTS
viously defined DM search region. In a multiton detector

SI WIMP-nucleon cross section [cm2]10−42LArによるDM探索

12

DarkSide-20k

次期計画：DarkSide-20k → ARGO

- 2相検出器- DS20k: 地下Ar (1/1400x) 30-50 ton,

ARGO : 地下Ar (1/1400 x (1/10)n), 500 ton- キセノン検出器と異なり，Standard-WIMP Searchと低エネルギー探索を

L.Rignanese@ ICHEP2020

両立することは難しい (BG量とDepleted-Argon精製量の兼ね合い)=> それぞれの物理に特化した複数の検出器を構築できればよい-

XENON1T Excessの検証，Non-Standard WIMP探索

39Arを大気アルゴンの10-6まで抑えたLArをO(1ton)用意できれば到達できる- 光量の確保 and/or 高電場印加により，低エネルギー側への感度が向上できないか
通常のWIMP Search (>100 keVの原子核反跳信号) では，波形弁別が非常に有効=> 39Arへの要請は主にトリガー・パイルアップ，

1相検出器であれば要請は小さくなる (1/100@500tでパイルアップは回避)

液体アルゴン検出器はWIMP/Non-WIMP双方に対して魅力的なデバイス: 非常に優れた粒子識別能力

纏め: 低エネルギー事象 (~Sub-keV) に対する大きな信号量 (観測量)
長寿命放射性同位体39Arの除去が絶対的に必要: Xe1Tレベルには，現在までの達成値 (1/1400) の更に1/1000が必要: 39Ar含有量を抑えたアルゴンの研究がDarkSideを中心に進められている
液体キセノン検出器と比べると...
: 同程度のシンチレーション検出効率，電子検出効率: 入手が容易 (安価) であり，速い (多種多様な) 研究開発が可能，

ただし大型実験の実現には，39Arを除去したアルゴンの確保が最大の障壁となる: 新物理の示唆に対しては大変意義の高い相互検証になる (検出器技術の類似性，核種依存性)
これまで早大(ANKOK)では低エネルギー領域に特化した研究・開発を進めてきた: 大光量 (~20 p.e./keV) 検出器，高電場検出器 (~3 kV/cm)，
低エネルギー・高電場下での液体アルゴン応答測定: 39Arの少ないアルゴンの精製・入手が確立されれば，できることが大きく増える

13

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