Calibration of Single Phase Liquid Argon Detectors

Transcription

1 Calibration of Single Phase Liquid Argon Detectors Kimberly J. Palladino MIT MiniCLEAN Collaboration 1

2 Outline Single Phase Liquid Argon technique Calibration Goals Internal calibration sources External gamma sources External neutron sources Optical calibration 2

3 Single Phase Liquid Argon Scintillation in LAr at 128 nm, requires wavelength shifter, TPB, to allow PMT detection Pulse shape discrimination (PSD) based on triplet lifetime of 1.6 us and singlet lifetime of 6 ns Fprompt, PSD variable, low (~0.3) for electronic recoils, and high (~0.8) for nuclear recoils Position reconstruction based on charge distribution and timing in larger detectors 3

4 Calibration goals Single PE Energy Scale Energy Resolution Position Recon. PSD Surface Events 39 Ar/PSD Leakage Neutrons Internal Sources Gamma Sources Neutron Sources Light Injection Electronic recoils Nuclear recoils 4

5 39 Ar Naturally occurring 39 Ar in atmospheric argon with activity of 1 Bq/kg First forbidden beta decay with analytically defined spectral shape Spectrum known to 1% down to 10 kev Endpoint at 565 kev Half-life of 269 years Uniform distribution in detector Continuous calibration 5

6 39 Ar: Energy Scale Triplet tail from 39 Ar allows constant monitoring of the single photoelectron spectrum and every individual PMT s gain Continuous detector health, including triplet lifetime MiniCLEAN will see ~800 khz of 39 Ar Light-yield measured in going from PE to kevee 1 day gives a statistical LY measurement to better than 1% 6

7 39 Ar: Position Reconstruction Uniformity gives r 2 relation in differential rates Allows daily studies of radial bias and position reconstruction Large datasets outside WIMP ROI Energy dependent studies 7

8 39 Ar: Pulse Shape Discrimination Probe of the electronic recoil rejecting pulse shape discrimination variable (F prompt ) with all events outside the fiducial volume But surface alpha and neutron events will have to be taken into account MiniCLEAN planning an 39 Ar Spike, 5-10x natural abundance after Dark Matter run to demonstrate PSD in larger detectors and investigate potential backgrounds UV ablated NM Geochronology Research Laboratory Fast reactor irradiation of KF/KCl utilizing 39 K(n,p) 39 Ar as is done in radiometric dating 8

9 83 Kr m 83 Rb (trapped in charcoal) decays with a half-life of 86.2 days to 83 Kr m 75% of the time, which, as a Noble gas flows into the detector 83 Kr m energy spectrum after background subtraction in MicroCLEAN 83 Kr m subsequently emits two conversion electrons with a total energy of 41.5 kev and a half-life of 1.83 hours Calibrates energy as a function of position -> no sign of freeze out in MicroCLEAN Lippincott et al. Phys.Rev.C81: arxiv: Planned calibration for KATRIN arxiv.org: v1 and also studied for LXe detectors Kastens et al. JINST 5(2010) P05006 and Manalaysay et al. Rev. Sci.Instrum 81 (2010)

10 External Gamma Sources DEAP-3600 Additional energy and position calibration, especially for high radius events Tagged sources allow reduction of the 39 Ar background during calibration DEAP-3600 can study neck region events MiniCLEAN Isotopes 22 Na: e + and MeV γ used by both MicroCLEAN and DEAP-1, MiniCLEAN tagged source 60 Co: 1.17 and 1.33 MeV γ DEAP-3600 tagged source Also considered: 137 Cs: 662 kev γ 57 Co: 122, 136, 692 kev γ 10

11 Neutrons: D-D generator Nuclear recoil PSD and energy calibration, test neutron tagging and verify simulation physics Primary calibration through dd-interaction Using Schlumberger MiniTron allowing pulsed and DC mode operation At 40kV, the neutron yield is 10 3 n/uc resulting in 10 5 n/s at 50 uc 11

12 D-D Neutron Simulations MiniCLEAN studies show 1.1% of generated neutrons in fiducial volume and energy ROI, lower for larger, acrylic shielded DEAP-3600 J. Walding kevee, r<295 mm kevee, r>295 mm Liskien & Paulsen (1973) 12

13 D-D System Power supplies and control electronics operating since 2010 Moving from prototype canister (shown) to final canister Deployment system under construction at RHUL. Moveable with size of 1.0m x 0.8m x 2.8m 13

14 Neutrons: Hot PMT MiniCLEAN pursuing a Hot PMT calibration source to reproduce most dangerous neutron background Will mix 5.3 g of 238 U and 16g of 232 Th in melted PMT glass to produce 1 n/s M. Akashi-Ronquest Tagged source with scintillator to see alpha, n de-excitation gammas Currently prototyping with 2 lbs of uranium borosilicate with 16 g (1.8%) 238 U pre WW-II with more daughters, but expected rate of 3 n/s 14

15 Optical Calibration: DEAP-3600 Optics before and after TPB deposition LEDball in diffuser, lowered through neck: 425 nm before TPB deposition, 250 nm after Optics stability, timing Distributed light by fibers to PMTs,light will reflect into the detector Light leakage from neck: laser light injection 15

16 Optical Calibration: MiniCLEAN Probe visible and UV optics, and surface event position reconstruction 6 UV (254 nm) and 6 Blue (465 nm) LEDs, in the LAr with fibers running to face of pentagonal lightguides Kapustinsky pulser allows fast pulses as expected from prompt argon scintillation Kapustinsky trigger pulse 20 ns trigger pulse 16

17 Calibrators DEAP-3600 MiniCLEAN RHUL: dd-neutrons, LANL: 39Ar, gammas, Hot PMTs, 83Krm light injecton RAL: gammas, 83Krm MIT: dd-neutrons, 83Krm Sussex: light injection RHUL: dd-neutrons Queen s: 39Ar UNM: light injection SNOLab: 39Ar, gammas 17

18 Conclusion Both DEAP-3600 and MiniCLEAN have developed calibration plans with multiple handles on each experimental parameter 39Ar, though a background, is an excellent calibration source too! Both experiments will have exciting year s as they build, and calibrate, the detectors! 18

19 Collaborations 19

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