DM search with Migdal - Kobe University

Migdal効果による暗黒物質探索

風間慎吾名古屋大学 KMI / IAR

＠ミグダル観測検討会2020

2暗黒物質直接探索

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=3,4 only


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.


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


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



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

Migdal効果を用いた暗黒物質探索@XENON1T

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)



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)



- 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



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)



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)



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



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)



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)



• 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

DM search with Migdal - Kobe University

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