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3暗黒物質直接探索
Charge
LUX/LZPandaXXENON
ArDMDarkSide
CoGeNTCDEXDAMICSENSEINEWS-GDRIFTMIMACDMTPC
SIMPLEPICASSOCOUPPPICO
CRESSTCOSINUS
SuperCDMSEDELWEISS
DAMA DM-IceCOSINESABREANAISPICO-LONDEAPXMASS
χ χ
nuclear recoils
Light
Heat
• Liquid argon• Liquid xenon• Directional detectors• Low-threshold • Bubble chambers• Cryogenic bolometers• Scintillating crystals
nnnununununununununnnununuuuuuuunnnnnununnunnnunuuuuuuun clclclcclclclcllclclcllcclcccclcccccccccccccccclllclclccclllclcclcccccccllllclclccllccllclccccccccc eeeeeaaaaeeaaeeaaeeaaaeeaaeeaeeeeeeeeaeeeeeeeeaaeaeeeeaeeeeeaaeeeaeeeeaaeeeeaaaaeeeeeaaaaaeeeeeeaaeeeeeeeaaeaeeaaeaaaeaeearrrrrr rrrrrrrrrrrrrrrrrrrrrrrrrrrererereeeeeeeeeeeeeeeeeeereeeerrrecocococoooocococcc illllllllilillillllllililii ssssssssssssssssssssssss
CRESSTCCC
LUX/LZ//
XENONOOO
SENSEI
CDEXCC
EDELWEISSSSS
= Migdal効果を用いた探索を行った実験
4暗黒物質探索の現状 (without Migdal Effect)
101 102 103
WIMP mass [GeV/c2]
10−49
10−48
10−47
10−46
10−45
10−44
10−43
WIM
P-n
ucl
eon
σ SI
[cm
2]
XENON10 (2008)
XENON100 (2012)
LUX (2017)PandaX-II (2017)
XENON1T (1 t×yr, this work)
XENONnT (20 t×yr Projection)
ν discovery limitBagnaschi 2017Billard 2013
- 23.6 g CaWO4 (~15mK)
- NR threshold of 30.1 eVnr.
- Phonon and Scintillation signal
Low-mass (CRESST-Ⅲ)
High-mass (XENON1T)- ~1.3t LXe TPC
- NR threshold of ~4 keVnr
- Scintillation(S1) and Ionization(S2)signal
- ER threshold of
S1-S2: ~1 keVee S2-only: 186 eVee
Phys. Rev. D 100, 102002 (2019)
5Bremsstrahlung and Migdal effect
When a particle elastically scatters off xenon nucleus, the nucleus undergoes sudden momentum change with respect to the orbital atomic electrons, resulting in the polarization of the recoiling atom and the shaking of atomic electrons
These phenomena can lead to irreducible emission of Bremsstrahlung photon, as well as excitations and ionizations of atomic electrons (Migdal effect).
ER signals through the new detection channels significantly enhance the sensitivity to masses previously insensitive through the standard NR searches.
Bremsstrahlung Migdal effect
JHEP 03, 194 (2018)
6Migdal効果を用いた暗黒物質探索
CDEX-1B EDELWEISS-SURF LUX XENON1T SENSEI
DetectorGe (charge-only) No ER/NR discri.
Ge (heat-only) (above ground)
LXe TPC (S1-S2)
LXe TPC (S1-S2, S2-only)
CCD (Si)
(charge-only, 135 K)
Size 939 g 33.4 g 118 kg ~1.3 ton ~2g
Exposure 737.1 kg day0.03 kg day (1-day blind,
5-days unblind) 13,775 kg day S1-S2: 1 ton year
S2-only: 22 ton day~20 g day
Threshold 160 eVee 60 eVee ~1 keVee S1-S2: ~1 keVee S2-only: 186 eVee
O(1) eVee (詳細不明) (1,2,3,4 e-)
LUX (Xenon): “Results of a Search for Sub-GeV Dark Matter Using 2013 LUX Data”, arXiv:1811.1124
XENON1T (Xenon): ”A Search for Light Dark Matter Interactions Enhanced by the Migdal effect or Bremsstrahlung in XENON1T”, arXiv:1907.12771
EDELWEISS (Germanium): ”Searching for low-mass dark matter particles with a massive Ge bolometer operated above-ground”, arXiv:1901.03588
CDEX-1B (Germanium): “Constraints on Spin-Independent Nucleus Scattering with sub-GeV Weakly Interacting Massive Particle Dark Matter from the CDEX-1B Experiment at the China Jin-Ping Laboratory” arXiv:1905.00354
SENSEI (Si): “SENSEI: Direct-Detection Results on sub-GeV Dark Matter from a New Skipper-CCD”, arXiv:2004.11378
7Migdal効果を用いた暗黒物質探索CDEX-1B EDELWEISS-SURF LUX XENON1T SENSEI
DetectorGe (charge-only) No ER/NR discri.
Ge (heat-only) (above ground)
LXe TPC (S1-S2)
LXe TPC (S1-S2, S2-only)
CCD (Si)
(charge-only, 135 K)
Size 939 g 33.4 g 118 kg ~1.3 ton ~2g
Exposure 737.1 kg day0.03 kg day
(above ground)13,775 kg day
S1-S2: 1 ton year S2-only: 22 ton day
~20 g day
Threshold 160 eVee 60 eVee ~1 keVeeS1-S2: ~1 keVee S2-only: 186 eVee
O(1) eVee (1,2,3,4 e-)
Analysis
n=2,3 only
n=1: negligible (too tightly bound)
n=3 only
n=1,2: negligible (too tightly bound)
n=3,4 only
n=1,2: negligible (too tightly bound)
n=3,4 only
n=1,2: negligible (too tightly bound)
詳細不明
伊部さんたちの計算はIsolated atom assumptionのもと計算されている点に注意半導体中での計算は先週末に出た(2011.09496を参照)
n=5: neglected since the surrounding atoms in the liquid may influence the ionization spectrum
n=4: neglected since they are easily affected by Ge band structure due to the small binding energy
Because of the smaller gap for electron excitations, we find that the rate for the Migdal effect is much higher in semiconductors than in atomic targets.
8Migdal効果を用いた暗黒物質探索
CDEX-1B EDELWEISS-SURF LUX XENON1T SENSEI
Shell n=2,3 only n=3 only n=3,4 only n=3,4 only 詳細不明
シグナルの取り扱い
詳細不明
Recoil Energy (keV)-110 1 10 210
Que
nchi
ng F
acto
r
0.1
0.2
0.3
0.4
k = 0.20
k = 0.157
Sattler 66Chasman 68Jones 71-75Shutt 92Messous 95Baudis 98Simon 03EDELWEISS 07CoGeNT 07TEXONO 07TRIMLINDHARD
1411.4802
全てのエネルギー(Edet)がある1点で損失したと仮定
5GeV以下のmassでは、NRのエネルギー損失は少ないと仮定して無視
2GeV以下のmassでは、NRのエネルギー損失は少ないと仮定して無視
(詳細は後述)
Quenching effects on the heat energy scale for nuclear recoils in Ge cryogenic detectors have been shown to be very small
= ΔE
9不明な(怪しい)点?
- Migdal効果に関わるIonization electron, x-ray/Auger electron + NRの全てのエネルギー損失がほぼ一点で起こる。LXe TPCの場合、同時にER+NRが起こる場合の再結合モデル等はよく分かってない(ER, NRを独立だと思った時のレスポンスと同じではない?)
LUX/XENON1Tでは、NRの寄与が無視できる範囲のみ探索を行っているのでOK
- Migdal効果が起きた場合、例えばXe+の様に原子核はプラスの電荷を帯びている。この場合、検出器レスポンスは中性の時と異なる?
Bremsstrahlung Migdal effect
10Migdal効果を用いた暗黒物質探索
2−10 1−10 1 10 [keVee]detE
5−10
3−10
1−10
10
310
510
710
Cou
nts
[evt
s/ke
V/k
g/da
y]
NR
(n=2)+(n=3)
2 = 1 GeV/cχm2 cm-36 = 10SI
Nχσ
( )
Threshold160 eVee
n=2
n=3
n=4
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 [keVee]detE
2
4
6
8
10
Cou
nts
[evt
s/ke
V/k
g/da
y]
(b)
2 cm-3610×=1.4SINχσ,2=1 GeV/cχm
2 cm-3210×=2SINχσ,2=0.05 GeV/cχm
0.03 0.1 1 2Energy [keV]
102
103
104
105
Number
ofcounts[evts/keV]
Standard Spectra
Background Model
Analysis Threshold (60 eV)
Data
Excluded WIMP model: 0.7 GeV/c2, 9.8× 10−35 cm2
Excluded WIMP model: 2.0 GeV/c2, 4.5× 10−37 cm2
Excluded WIMP model: 10.0 GeV/c2, 1.1× 10−37 cm2
CDEX EDELWEISS
n=3 only
from the 5 days of non- blinded data
- どちらもn=4の寄与は解析では取り入れてない
- どちらもwell establishedなBGモデルはないので、discovery potentialはない (実験データを全てシグナルだと思ってコンサバにlimitをつけるだけ) ̶> XENON1Tで言うところのS2-only解析
- EDELWEISSは、6日分のデータのうち5日分をunblindし、カットなどを最適化し、残り1日分のデータを用いてlimitを計算
- XENON1Tの結果は後ほど
XENON1T検出器@LNGS 12EPJ-C 77 (2017) 12
Water tank - 700 t of pure water Cryogenics, and
purification
DAQ and slow control
Xenon storage (ReStoX), handling and Kr distillation
TPC - 248 3-inch PMTs (R11410-21, QE~34%@178nm)
- LXe mass: 3.2 t(total), 2.0t (active)
Cherenkov Muon Veto - 84 8-inch PMTs (R5912)
Cryostat and support structure for TPC
External calibration - 241AmBe (NR) - Neutron generator (NR)
Internal calibration - 83mKr (ER), - 220Rn (ER)
13LXe TPCの動作原理
E0 Nex
Ni
scintillation (S1)
ionizati
on
heat
excitationrecombination
atomic motion
de-excitation
ionizatione- drift,
acceleration in gas phase
proportional scintillation (S2)
escape
- 直接蛍光 (S1)が、反応点で生成され、上下のPMTで検出
- 電離電子は、電場によりGXeへ向かってドリフト
- 電子は一部がXe+イオンと再結合してS1を発生
- GXeまで辿り着いた電子は、より強い電場によりGXeへ引き抜かれて、比例蛍光(S2)を生成
- 反応点の3次元位置再構成が可能 - X/Y位置: top PMT arrayでのS2のヒットパターン - Z位置: 電子のドリフト時間 = Δt (s1, s2 )
- 粒子識別: (S2/S1)γ,e > (S2/S1)WIMP, neutron
電子反跳(今回の解析) 原子核反跳
~0.1kV/cm
~8kV/cm
1m
S2(電子信号
) [PE
]
S1(光信号) [PE]
原子核反跳電子反跳
v(drift) ~ 1.3 mm/us
14
S1 S2
drift time ( = z-position) Time (μs)
S1
S2Δt (bottom, top) ~ 700us L(bottom, top) ~ 1m
LXe TPC: Waveform & Hit-Pattern
XENON1T実験のWIMP探索結果 (without Migdal Effect)
XENON1T set the most stringent upper limit on SI WIMP-nucleon cross sections > 6 GeV
However, the sensitivity to low-mass WIMP is quite limited because of 3-fold PMT requirement for S1 (threshold~ 4 keVnr)
15
Electric recoil (ER) signals induced by Bremsstrahlung or Migdal effect enable us to lower the energy threshold
10 GeV
200 GeV
50 GeV
101 102 103
WIMP mass [GeV/c2]
10−49
10−48
10−47
10−46
10−45
10−44
10−43
WIM
P-n
ucl
eon
σ SI
[cm
2]
XENON10 (2008)
XENON100 (2012)
LUX (2017)PandaX-II (2017)
XENON1T (1 t×yr, this work)
XENONnT (20 t×yr Projection)
ν discovery limitBagnaschi 2017Billard 2013
6GeV
16Light / Charge Yield for LXe TPC
0.5 1 3 6 10 30 50Energy [keVnr]
5
10
15
20
25
NR
Photo
nyie
ld[p
hkeV
−1]
> 10% efficiency
XENON1T this result (82 V cm−1)
XENON100 (530 V cm−1)
Aprile 2005 (0 V cm−1)
Aprile 2006 (2 kV cm−1)
Aprile 2009 (0 V cm−1)
Plante 2011 (0 V cm−1)
Sorenson 2009 (730 V cm−1)
Manzur 2010 (0 V cm−1)
Manzur 2010 (1 kV cm−1)
LUX 2017 (180 V cm−1)
NEST v2.0 (82 V cm−1)
0.5 1 3 6 10 30 50Energy [keVnr]
3
6
9
12
15
NR
char
ge
yie
ld[e
−keV
−1]
> 10% efficiency
0.1 0.3 0.6 1 3 6 10 20Energy [keVee]
10
20
30
40
50
60
ER
photo
nyie
ld[p
hkeV
−1]
> 10% efficiency
XENON1T this result (82 V cm−1)
XENON100 (CH3T, 92 V cm−1, cred. region)
LUX (CH3T, 105 V cm−1)
LUX (127Xe, 180V cm−1)
PIXeY (37Ar, 200 V cm−1)
NEST v2.0 (82 V cm−1)
Error bars are stat. + sys.
0.1 0.3 0.6 1 3 6 10 20Energy [keVee]
20
30
40
50
60
70
80
ER
char
ge
yie
ld[e
−keV
−1]
> 10% efficiency
NR
ER
- Threshold (S1-S2): PMTに対する3-fold coincidence requirementで決まる: 4keV for NR信号
- ER信号が使えるようになれば、Thresholdは4 keVnr -> 1keVeeへ!
- Charge-only analysis (S2-only)が可能になれば、さらに1 keVee -> 0.186 keVeeへ!
For charge yield, there is a
0.186 keVee (127Xe) measurement from LUX
Phys. Rev. D 96, 112011
1e- produces ~30 PEs. Photo-detection eff ~ 10%
17Signal Spectrum: LXe TPC Ibe et al, JHEP03(2018)194
2 GeV 5 GeV0.1 GeV
ENR [keVnr] ENR [keVnr]ENR [keVnr]
E ER [keV
ee]
n = 4 n = 4
Ionization (ER)NR
0000....1111 GGeeeVVVV
EEEEEE ERERRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE[keV
ee]
E ER [keV
ee]
0.1 GeVn = 4
S2-only
S1&S2 S1&S2 S1&S2
S2-only S2-only
The contribution of n=5 is neglected since the surrounding atoms in the liquid may influence the ionization spectrum. The inner electrons n ≤ 2 are too tightly bound to give an appreciable signal.
WIMP masses below 2 GeV, nuclear recoil energy is almost negligible, so only the ionization signal is considered.
Above 2GeV, both NR and ER signals are produced simultaneously at the same position- We don’t know detector response for such interactions at all.
- Therefore, the only contribution from n = 3 and 4 also considered.
18Detection Efficiency and Signal Spectrum
S1& S2 1e- produces ~30 PEs. If we do not require any S1s, it enables to recover detection efficiency significantly
Energy threshold is 0.186 keVee
It is very difficult to construct well-established background models without S1 information
30% of the data was unblinded for choosing regions of interest (ROIs) in S2 and event selections.
S2-onlySignificant BG reduction is possible based on S2/S1 and fiducialization with position reconstruction in 3d.
However, detection efficiency is limited by the S1 requirement (3-fold PMT coincidence)
BG models are already established for the main analysis already published.
Re-interpretation of the main analysis, and treat the ER region as our signal region
Energy threshold is 1 keVee
Phys. Rev. Lett.121, 111302
0.1 0.5 1.0 2.0 3.0 5.0Electronic recoil energy [keV]
10−7
10−3
10
105
109
Rat
e[e
ven
ts/t
onne/
yea
r/keV
]
0.1 GeV/c2 WIMP (Migdal)
0.1 GeV/c2 WIMP (BREM)
1.0 GeV/c2 WIMP (Migdal)
1.0 GeV/c2 WIMP (BREM)
0.01
0.1
0.5
1.0
Eff
ecti
ve
exposu
re[t
onne-
yea
rs]
S1-S2 data
S2-only data
n=3,4 only 186 eVee
19ResultsS1& S2
cS1[PE]
100
200
500
1000
4000
cS2
b[P
E]
1keV1keV
2keV2keV
3keV3keV3
5keV
5keV
10keV10keVI.
MIGD (0.3 GeV/c2)
MIGD (0.5 GeV/c2)
MIGD (1.0 GeV/c2)
ER model
DM search data
2 3 5 10 25 70 100cS1[PE]
1
5
10
Rat
e[ev
ents
/PE
]
II. ER 68% cred. region
DM search data
500 1000 2000cS2b [PE]
0
10
20
30
Counts
III. 3<cS1<10PE
4 5 10 20 50 70Number of electrons
10−3
10−2
10−1
1
101
102
Rat
e[e
ven
ts/t
onne/
yea
r/e−
]
0.1 GeV/c2
0.5 GeV/c2
1.0 GeV/c2
Background
S2-only data
150 200 500 1000 2000 3000S2 [PE]
0.1 GeV/c2
0.5 GeV/c2
1.0 GeV/c2
S1 & S2 Analysis S2-only Analysis
Threshold ~1 keVee ~0.186 keVee
BG model Yes No
Sensitivity to Low Mass WIMP Not Good Good!
Discovery potential Yes! No (将来的にはYes?)
- S2-only解析では一部理解しているBG(Pb214)は差っ引いているが、基本的にはデータを全てシグナルだと思って、コンサバに制限を引くのみ
- single-electronも見えているが、BGが膨大のため基本的には>5electronを見ている
- 閾値を下げることができれば、100kg程度のLXe TPCでも1T/nTを超える結果(low mass WIMPに対して)を得ることができる
S2-only
20Results
10−41
10−38
10−35
10−32
10−29
MIGDBREM
MIGD
BREM
I. Spin-independent
EDELWEISS (MIGD)
CDEX (MIGD)
CRESST-III
LUX (MIGD)
NEWS-G
CDMSlite
DarkSide
S2-only data (XENON1T)
S1-S2 data (XENON1T)
0.08 0.1 0.2 0.5 1.0 2
mχ[GeV/c2]
10−35
10−32
10−29
10−26
10−23
MIGD
BREM
MIGDBREM
III. Spin-dependent
(neutron-only)
CRESST-Li (neutron)
CRESST-O (neutron)
CDMSLite (neutron)
S1-S2 data (XENON1T)
S2-only data (XENON1T)
10−32
10−29
10−26
10−23
LD
M-n
ucl
eon
cross
sect
ion
σ[c
m2]
MIGD
BREM
MIGD
BREM
II. Spin-dependent
(proton-only)
CRESST-Li (proton)
CDMSLite (proton)
S1-S2 data (XENON1T)
S2-only data (XENON1T)
- 100 MeV - 2GeVのmass regionでも、XENON1T実験が世界最高感度を達成することに成功
- CRESSTあたりがMigdal効果を用いた探索をしたら負ける?
- NR searchの結果と合わせてまとめると以下の図になる。
- Darkside (LAr TPC)のS2-only解析に一部負けているが基本的にlow/high-massの両極限でXENON1Tが世界最高感度
21Earth-Shielding Effect
10−41
10−38
10−35
10−32
10−29
MIGDBREM
MIGD
BREM
I. Spin-independent
EDELWEISS (MIGD)
CDEX (MIGD)
CRESST-III
LUX (MIGD)
NEWS-G
CDMSlite
DarkSide
S2-only data (XENON1T)
S1-S2 data (XENON1T)
0.08 0.1 0.2 0.5 1.0 2
mχ[GeV/c2]
10−35
10−32
10−29
10−26
10−23
MIGD
BREM
MIGDBREM
III. Spin-dependent
(neutron-only)
CRESST-Li (neutron)
CRESST-O (neutron)
CDMSLite (neutron)
S1-S2 data (XENON1T)
S2-only data (XENON1T)
10−32
10−29
10−26
10−23
LD
M-n
ucl
eon
cross
sect
ion
σ[c
m2]
MIGD
BREM
MIGD
BREM
II. Spin-dependent
(proton-only)
CRESST-Li (proton)
CDMSLite (proton)
S1-S2 data (XENON1T)
S2-only data (XENON1T)
10−1 100
10−41
10−38
10−35
10−32
10−29
Migdal
BREMMigdal
BREM
I. Spin-independent
CDEX (BREM)
EDELWEISS (Migdal)
CDEX (Migdal)
CRESST-III
LUX (Migdal)
NEWS-G
CDMSlite
DarkSide
S2-only data (XENON1T)
S1-S2 data (XENON1T)
0.06 0.1 0.2 0.5 1.0 2
mχ[GeV/c2]
10−35
10−32
10−29
10−26
10−23
Migdal
BREMMigdal
BREM
III. Spin-dependent(neutron-only)
CRESST-Li (neutron)
CRESST-O (neutron)
CDMSLite (neutron)
S1-S2 data (XENON1T)
S2-only data (XENON1T)
10−32
10−29
10−26
10−23
LD
M-n
ucl
eon
cross
sect
ion
σ[c
m2]
Migdal
BREM
Migdal
BREM
II. Spin-dependent(proton-only)
CRESST-Li (proton)
CDMSLite (proton)
S1-S2 data (XENON1T)
S2-only data (XENON1T)
• DM particle may be stopped or scatter multiple times when passing through Earth’s atmosphere, mantle, and core before reaching the detector (Earth-shielding effect)
• If the DM-matter interaction is sufficiently strong, the sensitivity for detecting such DM particles in terrestrial detectors, especially in underground laboratory, can be reduced or even lost totally.
verneを使用: http://dx.doi.org/10.5281/zenodo.1116305
22Low Energy ER excess?
cS1[PE]
100
200
500
1000
4000
cS2
b[P
E]
1keV1keV
2keV2keV
3keV3keV3
5keV
5keV
10keV10keVI.
MIGD (0.3 GeV/c2)
MIGD (0.5 GeV/c2)
MIGD (1.0 GeV/c2)
ER model
DM search data
2 3 5 10 25 70 100cS1[PE]
1
5
10
Rat
e[ev
ents
/PE
]
II. ER 68% cred. region
DM search data
500 1000 2000cS2b [PE]
0
10
20
30
Counts
III. 3<cS1<10PE
Low Energy ER excessはMigdalを見ているのでは?
仮にlow ER excess (2keV付近)がMigdalから来ていると仮定すると、2keV以下でもっと信号が見ていないとおかしい
23SUMMARYDirect dark matter detection experiments based on LXe are leading the search for GeV-TeV scale DM, but have limited sensitivity to sub-GeV WIMPs because of the small momentum transfer of WIMP-nucleus elastic scattering.
However, there is an irreducible contribution of inelastic signals that accompanies the elastic scattering, which leads to emission of photon and the excitations / ionizations of atomic electrons.
Bremsstrahlung and Migdal EffectXENON1T is currently leading the searches both in low & high mass regions!
10−2 10−1 100
mχ [GeV]
10−40
10−39
10−38
10−37
10−36
10−35
10−34
10−33
10−32
σn[cm
2]
SENSEI (90% CL)
Xe 100 kg-yr 2e−
Ge
Si
Current Results Future Prospect
1 kg-year, zero-BG, # of e/h >=2
2011.09496
現在の制限
(ν-BG only)
24SUMMARYDirect dark matter detection experiments based on LXe are leading the search for GeV-TeV scale DM, but have limited sensitivity to sub-GeV WIMPs because of the small momentum transfer of WIMP-nucleus elastic scattering.
However, there is an irreducible contribution of inelastic signals that accompanies the elastic scattering, which leads to emission of photon and the excitations / ionizations of atomic electrons.
Bremsstrahlung and Migdal EffectXENON1T is currently leading the searches both in low & high mass regions!
- Low massでの制限は、Migdal効果があって、そのレートは計算通りという過程に基づいている。
- α, β崩壊などでMigdal効果は見つかっているので(See backup)、NRでもおそらくあるはずだがNRではまだ未観測
- Let’s observe it with dedicated experiments!
Current Results