Liquid Noble R&D for dark matter and double beta decay Tom - PowerPoint PPT Presentation

Liquid Noble R&D for dark matter and double beta decay Tom Shutt Case Western Reserve University T. Shutt - Argonne, 1/11/2013 1

Dark matter and ßß decay with liquid nobles Double beta decay EXO XMASS Dark matter LUX / LZ / XENON1T DarkSide XAX / MAX / Darwin XMASS DEAP / CLEAN Xe Ar Ne T. Shutt - Argonne, 1/11/2013 2

Challenges • Dark matter: Two phase Xe TPC — Improve S1/S2 discrimination: Common goal: • Cathode HV near 500 kV detector masses of tons • Highest light yield to tens of tons — Kr removal — Xe purity for charge + light — External detector — Reduce backgrounds in PMTs plus other components • Dark matter: Two phase LAr TPC — Reduce huge 39 Ar background • PSD discrimination • Removal • Xe ßß decay — Backgrounds, backgrounds, backgrounds — Light collection — Ba tagging T. Shutt - Argonne, 1/11/2013 3

Self shielding of gamma backgrounds PMT • Dark matter: single low-energy Compton scatter must enter and escape scatter = L λ e − L P ( L ) ∼ λ • 136 Xe ßß Decay — Q=2480 keV endpoint, above most lines, except: • 208 Tl: 2614 keV, 100% BR • 214 Bi: 2448 keV, 1.57% BR — Simple self-shielding: − x P ( L ) = P o e λ • Weaker than DM case • Conclusion: ßß experiment requires much lower backgrounds in components. T. Shutt - Argonne, 1/11/2013 4

S1/S2 Discrimination C.E. Dahl, J. Kwong Electron recoil band width S1 [PE] 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 /S1)-ER mean 0.4 0.2 0.0 b (S2 -0.2 10 log -0.4 99.75% -0.6 -0.8 Recombination -1.0 ZEPLIN III: ~99.99% ~5 kV/cm XENON100 -1.2 10 20 30 40 50 Energy [keVnr] • Sophisticated understanding of underlying processes in Xe. — Now: NEST simulation — Postdiction of Zeplin III result • High field helps oblem.( (figure(from(M.(Szydagis)( • Light collection helps XENON10(level((730(V/cm)( • Calibration is challenge: tritiated methane source XENON100(level((530(V/cm)( XENON10( ( (LUX) ZEPLINQIII(levels((3.4(and( 3.9(kV/cm)( • Situation in LAr is largely unknown. T. Shutt - Argonne, 1/11/2013 5 5 NEST

  = ¡fraction ¡of ¡“prompt”/total ¡light     Pulse shape DEAP-1 data discrimination in LAr 120-240 pe 60 keVr thres. 9 with 8 pe/keVee • Remarkably good: roughly matched to very large 39 Ar background • Very sensitive to amount of light collection • DEAP-1: believe threshold is ~60 keVr ~7 ~12 ~30 • R&D: map to low energy, high separation T. Shutt - Argonne, 1/11/2013 6

Light collection • LAr: — Waveshifters • Needed because of XUV photons: PMTs, reflectors • Doesn’t poison LAr for charge drift — Large phase space for optical design, especially single- phase detector. — R&D: geometry, quality of waveshifter film: reflectivity Rate (mBq/p.e.) 20 • LXe 661.7keV 15 — PTFE has remarkably high reflectivity in LXe, 10 apparently consistent with 100%. 5 DarkSide10: 8.9 pe/keV • Not the gas in gas Xe under same conditions. 0 1000 2000 3000 4000 5000 6000 7000 S1 (p.e.) — Why? LUX: 8 pe/keV — Can this be reproducibly controlled? T. Shutt - Argonne, 1/11/2013 7

LAr: 39 Ar reduction • Raw background ~ 1 Bq/kg • Minimal goal for TPC running: reduce by 10-100. — Factor of ~10 8 would allow lowest threshold • Old Ar in underground gas, requires extensive separation system - Princeton Underground Argon Measurements Rate/(Bq/keV) — <6.5 mBq/kg AAr, @KURF UAr, @Surface -2 10 — 143 of 150 kg collected, stable UAr, @Surface, Muon Vetoed UAr, @KURF production at 1/2 kg/day -3 10 — NSF funded expansion up to 50 kg/ day -4 10 -5 10 -6 10 0 200 400 600 800 1000 Energy/keV T. Shutt - Argonne, 1/11/2013 8

High voltage • High voltage on cathode sets drift field Example: LUX HV feedthrough (Yale) — Key driver of S2/S1 disc. in Xe, at least. LUX • Difficult in both LXe and LAr W — Not a distinguished history to date Ra — Need > 100kV in Xe to improve discrimination in fi LZ beyond ~99.5% No • Feedthrough design pursued by several fl groups /experiments — Core challenge: passage through gas phase • Alternative - generate in liquid (e.g., Crockcroft Walton) • Electroluminesence in detector also a 100 kV achieved in 2 / 2 feedthroughs with no sign of breakdown or aging challenge Design appears scalable to — Demonstrated in small detectors at needed field ~300 kV T. Shutt - Argonne, 1/11/2013 9

PMTs • Hamamatsu R11410mod, 3” with high QE is PMT 238 U 232 Th 40 K 60 Co new “default” [mBq/ [mBq/ [mBq/ [mBq/ — Backgrounds ~ 20 times lower than PMT] PMT] PMT] PMT] previous 2” tube (R8778) R8778 9.5±0.6 2.7±0.3 66±2 2.6±0.1 — Beginning to become non-dominant compared to current TPC mechanics R11410 • Reliance on Hamamatsu! <0.4 <0.3 <8.3 2.0±0.2 MOD • QUPIDs - no longer being developed(?) R11410mod • PMTs unlikely to be replaced for DM -> highest possible coverage • SiPMTs being pursed by EXO — Light yield -> resolution, but background essential. T. Shutt - Argonne, 1/11/2013 10

External detector system: LZ, DarkSide • Veto • Near-hermetic background measurement: systematics Active Xe Liquid Xe Skin Scint. • LZ n capture — Neutron and gamma vetoing — Xe “skin” — Gd-loaded LAB scintillator Ti PTFE γ — “Daya-Bay” architecture • DarkSide Dark Side — Neutron veto — B-loaded scintillator -> n-alpha • Doesn’t require high gamma efficiency — SS vessel with high PMT count LZ • Relative importance decreases as mass increases: self shielding T. Shutt - Argonne, 1/11/2013 11

Materials backgrounds • Ti - are LUX Ti backgrounds reproducible? How low are they? • How low can PMTs go? • Rn control — Rn in liquid, from all components: need few mBq in Xe TPC • Requires SNO/Borexino “lite” emanation program — Rn daughters on PTFE. • alpha-n • Pb recoil in single-phase - acute issue. — Rn daughters in PTFE? • Kr in Xe, 39 Ar in LAr • ßß decay: everything. PMTs far from being allowed, all materials require extreme cleanliness — Screening an enormous challenge. — Need whole-body screener with radically lower backgrounds T. Shutt - Argonne, 1/11/2013 12

Xe purification • Electron drift over meters is significant challenge in LXe — apparently harder than LAr. • Commercial heated getter removes impurities: challenge is liquid circulation • LUX, others: high efficiency dual-phase heat exchanger • Analytical techniques: simple RGA + novel cryo-trap (UMD) • Liquid purification — Pump — Variation of spark purifiers LZ 0.5 ppt Kr scheme 184 Temperature (K) 0 slpm 7.2 slpm 42.0 slpm 183 182 IR Shield Cryostat Can 181 Xenon Vessel Flange 180 Displacement Blocks 179 178 177 176 Power (W) 0 2000 4000 6000 8000 10000 IR Shield 40 Cryostat Can Xenon Vessel Flange 30 Displacement Blocks Heater Power open leak valve 20 10 T. Shutt - Argonne, 1/11/2013 0 13 0 2000 4000 6000 8000 10000 Time (s)

Kr separation from Xe: dark matter • Equivalent pp-solar neutrino rate is 0.3 ppt. — 0~.01 ppt for good pp-solar measurement • Commercial Xe typically ~100 ppb. • LUX - chromatography at ~< 2 ppt @ 8 kg/day • XMASS, XENON100 - distillation - XMASS: < 2 ppt at 4.7 kg/ day • Sub ppt: — Key is sampling system — Emanation / leaks need serious attention for sub ppts. • Pre-bake of all required plastic T. Shutt - Argonne, 1/11/2013 14