[PPT] - Light Dark Matter Search with Liquid Argon Masayuki Wada INFN PowerPoint Presentation

SLIDE 1

Light Dark Matter Search with Liquid Argon

Masayuki Wada INFN Cagliari, Italy June 5 2019 Light Dark Matter Workshop at Fermilab

1

SLIDE 2

Liquid Xenon

Denser & Radio pure
Lower energy threshold
Higher sensitivity at low mass WIMP

FEATURES OF NOBLE LIQUID DETECTORS

▸ Dense and easy to purify (good scalability, advantage over solid targets) ▸ High scintillation & ionization (low energy threshold, not low enough to search < 1 GeV/c2 DM) ▸ Transparent to own scintillation For TPC ▸ High electron mobility and low diffusion ▸ Amplification for ionization signal ▸ Discrimination electron/nuclear recoils (ER/NR) via ionization/scintillation ratio

2

Liquid Argon

lower temperature (Rn purification is

easier)

Stronger ER discrimination
Intrinsic ER BG from 39Ar
Need wavelength shifter

SLIDE 3

Liquid Xenon

Denser & Radio pure
Lower energy threshold
Higher sensitivity at low mass WIMP

FEATURES OF NOBLE LIQUID DETECTORS

▸ Dense and easy to purify (good scalability, advantage over solid targets) ▸ High scintillation & ionization (low energy threshold, not low enough to search < 1 GeV/c2 DM) ▸ Transparent to own scintillation For TPC ▸ High electron mobility and low diffusion ▸ Amplification for ionization signal ▸ Discrimination electron/nuclear recoils (ER/NR) via ionization/scintillation ratio

2

Liquid Argon

lower temperature (Rn purification is

easier)

Stronger ER discrimination
Intrinsic ER BG from 39Ar
Need wavelength shifter

SLIDE 4

FIG. 4.

Energy distribution of the events remaining in the data set after all data selection cuts. As an example, the expected spectrum for a WIMP of 6 GeV=c2 and a spin-independent WIMP-nucleon scattering cross section of 1.5 × 10−41 cm2 is also shown. The corresponding nuclear recoil energy scale is indicated on the top axis. The charge yield model assumed here has a cutoff at 0.7 keV, which truncates the WIMP spectrum.

SENSITIVE TO LOW DARK MATTER

COMPARISON WITH XENON100

▸ DS-50 has lower BG at the lowest Ne bins. ▸ Ar sees more events with given WIMP mass

and cross section.

3

0.5 1 1.5 2 2.5 3 3.5 [keV]

ne recoil

E

1 −

10 1 10

2

10 day] × kg × Events / [keV All XENON100 One S2 Single Scatters

NR energy

Phys. Rev. D 94, 092001 (2016)

C

n

v e r t w i t h t h e i r i

n

i z a t i

n

y i e l d XENON100 DarkSide-50

BG [evt/keVnr/kg/d] 0.5 in [0.7, 1.7] keVnr 0.2 @ 1.1 keVnr BG [evt/keVnr/kg/d] 0.07 in [3.4, 9.1] keVnr 0.5 @ 6 keVnr Analysis threshold 0.7 keVnr 0.6 keVnr

DS-50

0.5 1 1.5 2 2.5 3 [keV]

R

E

4 −

10

3 −

10

2 −

10

1 −

10 1 10 [1/keV/kg/day]

R

dR/dE

2

cm

41

=10 σ ,

2

=3 GeV/c

W

M Xe Ar

WIMP spectra in Xe and Ar Xe Ar XENON100

SLIDE 5

XY Reconstruction Introduction

23

e- e- e-

Ar

DARKSIDE-50

THE TIME-PROJECTION CHAMBER (TPC)

Nuclear Recoil (NR)

acquired charge ∫(S1) ≪ ∫(S2) ∫(S1) ≤ ∫(S2) time time

S2/S1 ratio and Pulse Shape Discrimination (PSD) WIMPs will generate nuclear recoils (NRs) Ar Ar Ar Ar Ar Ar Ar Ar Ar

n

Ar Ar Ar Ar Ar

e-

Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar

4

DM S1 e- e- e- Edrift Emult z∝tdrift

liquid argon (LAr)

x-y position

Ar

from S2 light fraction

Ar

S1 S2 S2 S1

acquired charge

Electron Recoil (ER)

Ar Ar Ar Ar

e- S2 e-

WIMP-like signal!

SLIDE 6

XY Reconstruction Introduction

23

e- e- e-

Ar

DARKSIDE-50

THE TIME-PROJECTION CHAMBER (TPC)

Nuclear Recoil (NR)

acquired charge ∫(S1) ≪ ∫(S2) ∫(S1) ≤ ∫(S2) time time

S2/S1 ratio and Pulse Shape Discrimination (PSD) WIMPs will generate nuclear recoils (NRs) Ar Ar Ar Ar Ar Ar Ar Ar Ar

n

Ar Ar Ar Ar Ar

e-

Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar

4

DM S1 e- e- e- Edrift Emult z∝tdrift

liquid argon (LAr)

x-y position

Ar

from S2 light fraction

Ar

S1 S2 S2 S1

acquired charge

Electron Recoil (ER)

Ar Ar Ar Ar

e- S2 e-

WIMP-like signal!

Cannot See! Cannot See!

SLIDE 7

LOW NE EVENTS IN DARKSIDE-50

BACKGROUND

▸ The events in Ne<4 are delayed electrons related to impurities. ▸ The origin of the excess at low Ne events (4<Ne<10) is

unknown and under investigation.

5

5 10 15 20 25 30 35 40 45 50

e

N

3 −

10

2 −

10

1 −

10 1 10

2

10 day] × kg ×

e

Events / [N

Data G4DS MC All

rays

γ Cryostat

rays

γ PMTs Kr

85

Ar +

39 2

cm

40

=10

χ

σ DM spectra

2

=2.5 GeV/c

χ

M

2

=5.0 GeV/c

χ

M

2

=10.0 GeV/c

χ

M

1 2 3 4 5 6 7 8 9 10 11 12 131415 ]

nr

E [keV 1 2 3 ]

ee

E [keV

10 1 10

2

10

3

10

Delayed electrons

SLIDE 8

DARKSIDE LOW MASS

CRITERIA FOR FUTURE LAr TPC

▸ Low activity of 39Ar ▸ Low impurity ▸ good electron lifetime ▸ low rate of the single

electron events

▸ Ultra-pure photo-sensor ▸ Pure (or no) cryostat

6 Membrane Cryostat AAr UAr

Field cage Light guide

Acrylic

Gas pocket SiPM array

Fiducial volume

SLIDE 9

39Ar SUPPRESSION

FURTHER DEPLETION OF Ar

Urania (Underground Argon):

Expansion of the argon extraction

plant in Cortez, CO, to reach capacity

f 100 kg/day of Underground Argon

Aria (UAr Purification):

Very tall column in the Seruci mine in

Sardinia, Italy, for high-volume chemical and isotopic purification of Underground Argon. A factor 10 reduction of 39Ar per pass is expected.

r

7

~350 m

SLIDE 10

]

2

[GeV/c

χ

M

1 −

10 × 5 1 2 3 4 5 6 7 8 910 ]

2

[cm

SI

σ Dark Matter-Nucleon

49 −

10

48 −

10

47 −

10

46 −

10

45 −

10

44 −

10

43 −

10

42 −

10

41 −

10

40 −

10

39 −

10

yr proj. × DS-LM 1 t DS-50 2018 DS-50 BQF DS-50 No QF COGENT 2013 LUX 2017 XENON1T 2017 PICO-60 2017 CDMSLite 2017 CRESST-III 2017 PandaX-II 2016 XENON100 2016 CDMS 2013 CRESST 2012 DAMA/LIBRA 2008 Neutrino Floor

LOW MASS WIMP SEARCH

SENSITIVITY

▸ Exposure: 1 tonne year ▸ 39Ar: 1µBq/kg (currently ~1mBq/kg in

DS-50) with 39Ar depletion in Aria plant

▸ SiPM: 50 times lower contribution than

currently achieved in DS-20k (cleaner and reduced electronics)

▸ Acrylic: 5 mm thickness with the activities

achieved by JUNO collaboration.

▸ No cryostat ▸ Analysis threshold: 2 Ne (~0.4 keVnr) ▸ No systematic uncertainties are included 8

1 tonne year projection threshold: 2 Ne

39Ar: 1µBq/kg

SLIDE 11

ASSUMPTIONS

▸ No BGs except the internal 39Ar BG, external gamma BGs

from the detector components, and coherent neutrino BGs (the neutrino electron scattering is an order smaller and ignored).

▸ Low Ne events will be suppressed via deep fiduciallization,

pulse shape, and reduced activity in the active volume.

9

SLIDE 12

42 −

10

41 −

10

40 −

10

39 −

10

38 −

10

37 −

10

36 −

10

= 1

DM

F DarkSide-50 DarkSide-LM Proj. Bq/PDM µ Ar 1

39

Bq/kg µ 1 XENON100 XENON10

10

2

10

3

10 ]

2

[MeV/c

χ

m

39 −

10

38 −

10

37 −

10

36 −

10

35 −

10

34 −

10

33 −

10

32 −

10

31 −

10

2

1/q ∝

DM

F DarkSide-50 DarkSide-LM Proj. Bq/PDM µ Ar 1

39

Bq/kg µ 1 XENON100 XENON10

]

2

[cm

e

σ Dark Matter-Electron

DARKSIDE-50

SUB-GEV DARK MATTER SEARCH

▸ Ultra-light DM (m𝜓≪1 GeV) scatter off

electrons

▸ DM signals are also ER. ▸ The same measured spectrum as the

WIMP search can be used.

▸ Two extreme cases of Dark Matter

form-factor are considered

▸ FDM=1 heavy mediator ▸ FDM∝ 1/q2 light mediator ▸ The dashed lines are with assumptions

f 1 uBq/kg for 39Ar, 1 uBq/PDM, Cu

cryostat, 80,000 kg day, and 2e- threshold

10

SLIDE 13

ε

2 −

10

1 −

10 1 ]

nr

/keV

[e

y

Q 1 2 3 4 5 6 7 8 9 10

]

nr

[keV

Ar

E 1 10

2

10

Ar Data ARIS SCENE AmBe - AmC - ARIS - SCENE Joshi et al. 2014 Joshi et al. 2014 Cross Calibrated

TODO

NR IONIZATION YIELDS

▸ MC + Ionization model [1] fit to

NR data from AmBe and AmC.

▸ Need calibration points at low

recoil energies

10 20 30 40 50 60 70 80 90 100

e

N 100 200 300 400 500 600 700 800 900

e

Events / N

AmBe Data

241

G4DS Fit Single S2 S1 + S2

10 20 30 40 50 60 70 80 90 100

e

N 10 20 30 40 50 60 70 80 90 100

e

Events / N

C Data

13

Am

241

G4DS Fit Single S2 S1 + S2 γ C

13

Am

241

AmBe neutron source AmC neutron source

number of electrons number of electrons

Argon

[1] F . Bezrukov, F . Kahlhoefer, and M. Lindner, Astropart. Phys. 35, 119 (2011).

11 Reduced Energy