Liquid Argon Detectors at the Single(ish) Electron Limit Graham - - PowerPoint PPT Presentation

Liquid Argon Detectors at the Single(ish) Electron Limit

Graham Giovanetti Princeton University

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2

1/1400

AAr 39Ar

argon has a naturally occurring beta- emitting isotope, 39Ar

DarkSide-50

3

4

located at LNGS Hall C

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1,000-tonne Water Cherenkov Cosmic Ray Veto 30-tonne Liquid Scintillator Neutron and γ Veto inner TPC

and installed in veto detector

liquid argon TPC concept

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S1 e- e- e- S2

electron recoil nuclear recoil >108 rejection from S1 PSD

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can we reduce the energy threshold?

S1 scintillation signal threshold at 2 keVee = 10 keVnr S2 ionization signal threshold at <0.1 keVee = 0.4 keVnr

• PMTs have negligible dark rate at 88 K
• center PMT sees ~23 photoelectrons per electron
• high trigger efficiency
• single electron sensitivity
• lose PSD, Z-reconstruction, and S2/S1

1 keVee ~ 5 keVnr ~ 25 e- ~ 10 S1 PE ~ 600 S2 PE

NB: very rough comparison, these don’t scale linearly

• Phys. Rev. Lett., vol. 121, 081307 (2018)
• Phys. Rev. Lett., vol. 121, 111303 (2018)

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• e

N 20 40 60 80 100 day] × kg ×

• e

N [0.5 / Events

3 −

10

2 −

10

1 −

10 1 10

2

10

3

10

First 100 days Last 500 days d) (500 Single S2 d) (500 S1 + S2

• e

N

50 100

day] × kg ×

• e

[N / Events

0.2 0.4 0.6 0.01 ± 0.11 = Ratio BR L/K First 100 days

Last 500 days d) (500 Single S2 d) (500 S1 + S2

day] kg [N / Events

can we reduce the energy threshold?

S1 scintillation signal threshold at 2 keVee = 10 keVnr S2 ionization signal threshold at <0.1 keVee = 0.4 keVnr

9

can we reduce the energy threshold?

0.5 1 1.5 2 2.5 3

• e

N

2 −

10

1 −

10 1 10

2

10 day] × kg ×

• e

N [0.05 / Events

PE S2=30 Center PMT

DS-50 DATA Getter Off Getter On Fit

• 1 Ext. e

's

• 2 Ext. e

S1 scintillation signal threshold at 2 keVee = 10 keVnr S2 ionization signal threshold at <0.1 keVee = 0.4 keVnr

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electron detection efficiency

10 20 30 40 50 60 70 80 90 S2 [PE] 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Acceptance

Fiducialization Trigger efficiency × <0.15)

90

S2 Identification (f ×

single electron

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electron recoil energy scale

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electron recoil energy scale

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background rates

approximate - normalized at 10 e-

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

1 −

10 1 10

2

10

3

10 day] × kg ×

ee

Events / [keV

14

background rates

approximate - normalized at 10 e-

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

1 −

10 1 10

2

10

3

10 day] × kg ×

ee

Events / [keV

15

continuum background

1/1400

AAr 39Ar

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background rates

approximate - normalized at 10 e-

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

1 −

10 1 10

2

10

3

10 day] × kg ×

ee

Events / [keV

17

single electron events

0.5 1 1.5 2 2.5 3

• e

N

2 −

10

1 −

10 1 10

2

10 day] × kg ×

• e

N [0.05 / Events

PE S2=30 Center PMT

DS-50 DATA Getter Off Getter On Fit

• 1 Ext. e

's

• 2 Ext. e

18

background rates

approximate - normalized at 10 e-

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

1 −

10 1 10

2

10

3

10 day] × kg ×

ee

Events / [keV

19

4-7 e- excess

• incorrectly modeled beta spectrum?
• tritium?
• ther

Kossert & Mougeot, Appl. Radiat. Isot., Vol. 101 (2015)

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background rate in DarkSide-50

arXiv:1202.6073, see Scott’s introductory talk

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what about a future detector?

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

1 −

10 1 10

2

10

3

10 day] × kg ×

ee

Events / [keV

• we’ll imagine an optimized electron recoil detector spun-off of

DarkSide-20k (next-gen DarkSide TPC)

• ~200 kg fiducial mass

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assume no 85Kr and 100x reduction in 39Ar

• better handling at URANIA (UAr extraction in Colorado)
• and/or cryogenic distillation at ARIA

25 M

SERUCI-0 pilot plant

r

~350 m

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reduce other internal backgrounds below 39Ar

• larger volume improves

fiducialization

• switch from PMTs to SiPMs
• optimize geometry to minimize

number of SiPMs

• eliminate TPC cryostat and

use a large argon buffer volume

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ignore single e- and 4-7 e- excess

thanks to C. Savarese

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approximate bkg rate in new experiment

arXiv:1202.6073, see Scott’s introductory talk