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Double Beta Potential of Zeplin

Double Beta Potential of Zeplin. Can we do HDM search with CDM detectors? Very, very preliminary assessment Roland Lüscher. Zeplin: brief summary of DM programme Doing bb-search with a DM detector?. WIMP. Predicted DM spectrum. M D. M T. total event rate (point like nucleus). R o.

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Double Beta Potential of Zeplin

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  1. Double Beta Potential of Zeplin Can we do HDM search with CDM detectors? Very, very preliminary assessment Roland Lüscher • Zeplin: brief summary of DM programme • Doing bb-search with a DM detector?

  2. WIMP Predicted DM spectrum MD MT total event rate (point like nucleus) Ro event rate per unit mass dR -ER/Eor e = dE Eor R incident energy recoil energy kinematic factor = 4MDMT/(MD + MT)2 10 8 Raw spectrum 6 Event Rate (events/kg/day) 4 2 Noise corrected 0 Nuclear Recoil Limits -2 10 15 25 0 5 20 Event Energy (keV) Direct Detection • Kinematics: Background rejection tools: (1) Nuclear recoil discrimination (2) Directional signal

  3. 40keV Electron Recoil Gamma ray (or beta decay) Different dE/dX, Range, etc. WIMP v = 230km/s M≈ 200GeV Scintillation Phonon Ionisation Signal Channel Differences Ge, Si Pulse Shape Differences NaI, CsI, Xe Signal Channel Differences Xe 40keV Nuclear Recoil +- +- +- +- Background Discrimination • Nuclear recoil discrimination

  4. LXe: Why using it? • Heavy nuclei (A~130), sensitive to spin-independent interactions(Isi~A2). • Isotopes with large spin-dependent factors, Isd~0.3 for 129Xe (23Na in NaI or 73Ge in Ge ~0.1) ... • … as well as easier enrichement. • Scintillation in UV (l=175 nm), low visible energy threshold. • Large quenching factor for Xe recoils g(A)>0.2 (I in NaI: g(A)=0.09, Na: g(A)~0.3), low recoil energy threshold. • Low background • Scintillation properties enables Pulse-Shape Discrimination (PSD) between background (electron recoil) and nuclear recoil events. • Interesting ionisation properties … • Scale up possibilities (up to 1 ton ?)

  5. Triplet Singlet 3ns 27ns 2Xe 2Xe ZEPLIN I Xe+ Ionisation +Xe Electron/nuclear recoil Xe2+ Excitation +e- (recombination) Xe* Xe** + Xe +Xe Xe2* 175nm 175nm

  6. Counts vs. time Xe temp vs. time room temp vs. time Boulby stub 2 laboratory xenon purification Top of veto Pb shielding ZEPLIN I Installation

  7. ZEPLIN I Energy Resolution 57 Co Calibration 122 keV peak 136 keV peak (10%) Linear response 1.5 - 2.5 p.e./keV (57Co calibration is effective point source) Resolution 30 keV X-ray 92 keV recoil e- 106 keV recoil e-

  8. Z1 Energy Calibration Multi-source calibration Variation in yield commensurate with volume response matrix Geant4 Simulation of 57Co calibration With/without energy resolution

  9. Noise trigger Single PMT event Double PMT event Scan through one PMT plane Bulk events Turret events Fiducial volume cut Trigger condition is set to ‘free-run’ Uniformity, light collection • Part of detector response matrix • 17% best, 14% bulk • Falls to 4% below Xe delivery pipe • Light collection simulations allow S3 calculations • S3 cut < 0.408 (66% on 1: 0.5 + 0.5/3) • Fiducial volume 3.1kg • (excluding turrets + ~1cm below) Scan through detector girth

  10. cPCI DAQ system • Acqiris cPCI digitizers, 1ns sampling, 8 bits • Mean data rate: 2Hz • Max rate: 800 Hz (cal) Deadtime ~1 ms • Dual range DAQ: • one covers ‘high’ energy up to 150 keV (daily E cal) • 2nd is the dark matter interval, up to 40 keV. (less digital noise at low E)

  11. ZEPLIN I Discrimination 10-20keV • Using different fitting techniques • Exp, Mean, mean to 90%, median • Fitted ‘gamma’ density function in 1/t • Surface calibrations data to 7keV • Surface ambient neutrons to 4 keV Gamma source Neutron source

  12. Statistical methods • 91 day livetime, 280kg.days data •  calibration from veto-ed events • -density fit (actually in 1/t) as guide: smooth slope • Analysis: 2 over signal region, poisson stat on tail c2 Poisson

  13. ZEPLIN I limit • ‘Standard’ DM model • Nuclear physics: Quenching = 0.2, Form factor

  14. Dual Phase Xenon Applying an electric field e- • Prevents (part of) recombination • Measure both scintillation and ionisation Electro-luminescence Gas phase Active, liquid phase Primary-Scintillation e- or nucl. recoil g

  15. Dual phase discrimination .. but still keeping some interesting pulse shape properties on primary Active volume: 30kg LXe

  16. Zeplin 3 Gas phase Active volume 6kg Inverse field region … 31 PMTs

  17. Projected limits

  18. Zeplin Max - towards 1t ? Modular approach ? Zeplin-2 type Zeplin-1 type Zeplin-3 type

  19. LXe: Why using it? • Low background • Scintillation properties enables Pulse-Shape Discrimination (PSD) between background (alphas) and electron recoil events. • Interesting ionisation properties … • Scale up possibilities (up to 1 ton ?) • 3 candidates to look at: • 136Xe, with E0 = 2.48 MeV, 8.9% natural abundance • 134Xe, with E0 = 0.85 MeV, 10.4% natural abundance • 124Xe, with E0 = 0.82 MeV, 0.1% natural abundance • Phase-space factor, hence rate, is going with E05 • World yearly of enriched 124Xe is … 5 liters! - - ++

  20. bb in 136Xe Gotthard experiment: 5.3kg Xe TPC 62.5% 136Xe

  21. Limit on 136Xe bb? T 1/2 = (NA/0.136)Ae(M/(sB))1/2 A: Isotopic abundance 8.9% or 65% e: Detector efficiency nearly 1 M: Target mass 3.1 kg, 30kg, 250kg s: Energy resolution 40 keV (p.e. statistics) 60 keV (extrapol. from low E, 1.2√E) B: Background rate? ? ? What is it in Z1? Can I extrapolate to Z2? To Zmax?

  22. Z1: Background at high E Pulse Shape analysis at high Energy gammas Alphas (from different locations)

  23. Z1: possible limit on bb ‘Gamma-like’ background: ~ exponential shape Assuming a spectroscopic smearing due to the varying light collection efficiency through the active volume - a quick ‘back of the envelope’ estimate: 0.05 counts/kev/kg/year T1/2 > 1.9 x 1024 yr(90%CL, assuming enrichment of 65%, 1yr data) => 0.9 - 2.5 eV Dama, 6.5kg LXe DM detector, 68.8% 136Xe: T1/2 > 1.2 x 1024 yr PLB, 546 (2002) 23 Gotthard, 5.3kg Gxe TPC, 62.5% 136Xe: T1/2 > 4.4 x 1023 yr PLB, 434 (1998) 407

  24. Extrapolation to Z2 and ZMax Zeplin 2: 30kg, same background rate (?) > 5.9 x 1024 yr, < 0.5 - 1.4 eV Zeplin Max: 250kg module, same background rate (?) > 1.7 x 1025 yr, < 0.3 - 0.8 eV To be compared with: < 0.1eV (Cuore), < 0.02 eV (Genius, EXO) (for 1 ton, 1yr) 0.35 eV (Heidelberg-Moscow claim) Competitive with large scale bb expt. … … but only if we can B (factor 10)

  25. Conclusion 128Xe 129Xe 130Xe 131Xe 132Xe 134Xe 136Xe 1.9 26.4 4.1 21.2 26.9 10.4 8.9 Odd Even Can we do HDM search with Zeplin? May be, yes! Slight problem: isotopic enrichment would be needed … ……… buy one get, one free?!? Well, what about a free cookie? WIMP spin in/dependant cross section studies - - would require some isotopic separation!

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