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 � 1

argon has a naturally occurring beta- emitting isotope, 39 Ar AAr 39 Ar 1/1400 � 2

DarkSide-50 � 3

located at LNGS Hall C � 4

and installed in veto detector 1,000-tonne Water Cherenkov Cosmic Ray Veto 30-tonne Liquid Scintillator Neutron and γ Veto inner TPC � 5

liquid argon TPC concept >10 8 rejection from S1 PSD S2 e- electron recoil e- e- S1 nuclear recoil � 6

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) � 7

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 3 10 day] day] day] 0.6 First 100 days L/K First 100 days BR Ratio = 0.11 0.01 ± 2 × 10 Last 500 days Last 500 days kg × kg 0.4 Single S2 (500 d) kg × Single S2 (500 d) - e 10 [N S1 + S2 (500 d) [N S1 + S2 (500 d) × 0.2 / / Events - Events e N 1 0 [0.5 0 50 100 N - e 1 − 10 / Events 2 − 10 3 − 10 0 20 40 60 80 100 N - e � 8

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 DS-50 DATA Center PMT Getter Off 2 10 day] Getter On Fit - × 1 Ext. e kg - 10 2 Ext. e 's × - e N [0.05 1 / PE Events S2=30 − 1 10 2 − 10 0 0.5 1 1.5 2 2.5 3 N - e � 9

electron detection efficiency 0.5 0.45 0.4 0.35 Acceptance 0.3 0.25 0.2 Fiducialization 0.15 Trigger efficiency × 0.1 S2 Identification (f <0.15) × 90 0.05 0 10 20 30 40 50 60 70 80 90 S2 [PE] single electron � 10

electron recoil energy scale � 11

electron recoil energy scale � 12

background rates E [keV ] nr 1 2 3 4 5 6 7 8 9 10 11 12 131415 2 10 1 2 3 approximate - normalized at 10 e - E [keV ] ee 3 10 Data -40 2 DM spectra σ =10 cm day] χ day] 10 G4DS MC All 2 M =2.5 GeV/c χ Cryostat -rays γ 2 × × 2 10 M =5.0 GeV/c kg kg χ PMTs -rays γ 2 1 39 85 M =10.0 GeV/c Ar + Kr χ × × ee - 10 Events / [keV e Events / [N − 1 10 1 − 2 10 − 1 10 3 − 10 0 5 10 15 20 25 30 35 40 45 50 N - e � 13

background rates E [keV ] nr 1 2 3 4 5 6 7 8 9 10 11 12 131415 2 10 1 2 3 approximate - normalized at 10 e - E [keV ] ee 3 10 Data -40 2 DM spectra σ =10 cm day] χ day] 10 G4DS MC All 2 M =2.5 GeV/c χ Cryostat -rays γ 2 × × 2 10 M =5.0 GeV/c kg kg χ PMTs -rays γ 2 1 39 85 M =10.0 GeV/c Ar + Kr χ × × ee - 10 Events / [keV e Events / [N − 1 10 1 − 2 10 − 1 10 3 − 10 0 5 10 15 20 25 30 35 40 45 50 N - e � 14

continuum background AAr 39 Ar 1/1400 � 15

background rates E [keV ] nr 1 2 3 4 5 6 7 8 9 10 11 12 131415 2 10 1 2 3 approximate - normalized at 10 e - E [keV ] ee 3 10 Data -40 2 DM spectra σ =10 cm day] χ day] 10 G4DS MC All 2 M =2.5 GeV/c χ Cryostat -rays γ 2 × × 2 10 M =5.0 GeV/c kg kg χ PMTs -rays γ 2 1 39 85 M =10.0 GeV/c Ar + Kr χ × × ee - 10 Events / [keV e Events / [N − 1 10 1 − 2 10 − 1 10 3 − 10 0 5 10 15 20 25 30 35 40 45 50 N - e � 16

single electron events DS-50 DATA Center PMT Getter Off 2 10 day] Getter On Fit - × 1 Ext. e kg - 10 2 Ext. e 's × - e N [0.05 1 / PE Events S2=30 1 − 10 2 − 10 0 0.5 1 1.5 2 2.5 3 N - e � 17

background rates E [keV ] nr 1 2 3 4 5 6 7 8 9 10 11 12 131415 2 10 1 2 3 approximate - normalized at 10 e - E [keV ] ee 3 10 Data -40 2 DM spectra σ =10 cm day] χ day] 10 G4DS MC All 2 M =2.5 GeV/c χ Cryostat -rays γ 2 × × 2 10 M =5.0 GeV/c kg kg χ PMTs -rays γ 2 1 39 85 M =10.0 GeV/c Ar + Kr χ × × ee - 10 Events / [keV e Events / [N − 1 10 1 − 2 10 − 1 10 3 − 10 0 5 10 15 20 25 30 35 40 45 50 N - e � 18

4-7 e - excess • incorrectly modeled beta spectrum? • tritium? • other Kossert & Mougeot, Appl. Radiat. Isot., Vol. 101 (2015) � 19

background rate in DarkSide-50 arXiv:1202.6073, see Scott’s introductory talk � 20

what about a future detector? • we’ll imagine an optimized electron recoil detector spun-off of DarkSide-20k (next-gen DarkSide TPC) • ~200 kg fiducial mass E [keV ] nr 1 2 3 4 5 6 7 8 9 10 11 12 131415 2 10 1 2 3 E [keV ] ee 3 10 Data -40 DM spectra =10 cm 2 σ day] χ day] 10 G4DS MC All 2 M =2.5 GeV/c χ Cryostat -rays γ 2 × × 2 10 M =5.0 GeV/c kg kg χ PMTs -rays γ 2 1 39 85 M =10.0 GeV/c Ar + Kr χ × × ee - 10 Events / [keV e Events / [N 1 − 10 1 2 − 10 1 − 10 − 3 10 0 5 10 15 20 25 30 35 40 45 50 N - e � 21

assume no 85 Kr and 100x reduction in 39 Ar •better handling at URANIA (UAr extraction in Colorado) •and/or cryogenic distillation at ARIA r 25 M ~350 m SERUCI-0 pilot plant � 22

reduce other internal backgrounds below 39 Ar •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 � 23

ignore single e - and 4-7 e - excess thanks to C. Savarese � 24

approximate bkg rate in new experiment arXiv:1202.6073, see Scott’s introductory talk � 25