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Starting Points (Collaboration ; Laboratory ) 1-kg HPGe : Magnetic Moment Results

Ultra-Low Energy Germanium Detectors for Neutrino-Nucleus Coherent Scattering and Dark Matter Searches. Starting Points (Collaboration ; Laboratory ) 1-kg HPGe : Magnetic Moment Results Physics & Requirements of ULEGe Detectors R&D on ULEGe Prototypes

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Starting Points (Collaboration ; Laboratory ) 1-kg HPGe : Magnetic Moment Results

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  1. Ultra-Low Energy Germanium Detectors for Neutrino-Nucleus Coherent Scattering and Dark Matter Searches • Starting Points (Collaboration ; Laboratory ) • 1-kg HPGe : Magnetic Moment Results • Physics & Requirements of ULEGe Detectors • R&D on ULEGe Prototypes • Results on Cold Dark Matter Searches (arXiv:0712.1645) • Status & Plans Henry T. Wong /王子敬 Academia Sinica /中央研究院 @ OCPA Workshop July 2008 Hong Kong

  2. TEXONO Collaboration Collaboration : Taiwan (AS, INER, KSNPS, NTU) ; China (IHEP, CIAE, THU, NJU) ; Turkey (METU) ; India (BHU) Program: Low Energy Neutrino & Astroparticle Physics Kuo Sheng (國聖)Power Reactor : KS NPS-II : 2 cores  2.9 GW

  3. Kuo Sheng Reactor Neutrino Laboratory Front Gate • 28 m from core#1 @ 2.9 GW • Shallow depth : ~30 meter-water-equivalent • Reactor Cycle : ~50 days OFF every 18 months

  4. Front View (cosmic vetos, shieldings, control room …..) Configuration: Modest yet Unique Flexible Design: Allows different detectors conf. for different physics Inner Target Volume

  5. quality Detector requirements mass On-Going Data Taking & Analysis • SM s(ne) • T > 2 MeV • R&D : • Coh. (nN) • T < 1 keV Results : • mn(ne) • T ~ 1-100 keV Reactor Neutrino Interaction Cross-Sections 1 counts / kg-keV-day

  6. Reactor Neutrino Spectra Evaluation… Reactor Operation Data Nuclear Physics

  7. Neutrino Electromagnetic Properties : Magnetic Moments requires mn0 e.g. • a conceptually rich subject ; much neutrino physics & astrophysics can be explored n-osc. : Dmn , Uij 0nbb : mn, Uij , nD/nM • mn: mn, Uij , nD/nM , n  g • fundamental neutrino properties & interaction ; necessary consequences of neutrino masses/ mixings ; in principle can differentiate Dirac/Majorana neutrinos • explore roles of neutrinos in astrophysics

  8. Magnetic Moment Searches @ KS • simple compact all-solid design : HPGe (mass 1 kg) enclosed by activeNaI/CsI anti-Compton, further by passive shieldings&cosmic veto • selection: single-event after cosmic-veto, anti-Comp., PSD • TEXONO data (571/128 days) ON/OFF)[PRL 90, 2003 ; PRD 75, 2007] • background comparable to underground CDM experiment : ~ 1 day-1keV-1kg-1 (cpd) • DAQ threshold 5 keV analysis threshold 12 keV

  9. Direct Experiments at Reactors KS Limit: mn(ne)< 7.4 X 10-11mB @ 90% CL • Search of mn at low energy •  high signal rate & robustness: • mn>>SM [ decouple irreducible bkg  unknown sources ] • T << En ds/dT depends on total fn flux but NOT spectral shape[ flux well known : ~6 fission-n ~1.2 238U capture-nper fission ] GEMMA-07 (Ge+NaI): mn(ne) < 5.8 X 10-11mB

  10. “Ultra-Low-Energy” HPGe Detectors • ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation • Prototypes built and studied (starting 2003) : • 5 g @ Y2L • 4 X 5 g @ KS/Y2L • 10 g @ AS/CIAE • segmented 180 g @ AS/KS • Built & being studied : 500 g single element •  GoalO[100 eV threhold1 kg mass1 cpd detector]physics : • nN coherent scattering • Low-mass WIMP searches • Improve sensitivities on mn • Implications on reactor operation monitoring • Open new detector window & detection channel available for surprises

  11. Standard Model Cross-Sections: Neutrino-Nucleus Coherent Scattering : • a fundamental neutrino interaction never been experimentally-observed • s~N2applicable at En<50 MeV where q2r2<1 • a sensitive test to Stardard Model • an important interaction/energy loss channel in astrophysics media • a promising new detection channel for neutrinos; relative compact detectors possible (implications to reactor monitoring); &the channel for WIMP direct detection ! • involves new energy range at low energy, many experimental challenges & much room to look for scientific surprises

  12. e.g. at QF=0.25 & 100 eV threshold • Rate ~ 11 kg-1 day-1 @ KS • c.f.nN (Ge;1 keV) @ accelerator ~ 0.1 kg-1 day-1 ; • ne-p (water) @ KS ~ 1 kg-1 day-1 Expected Interaction Rates at KS @ different Quenching Factors by-product : T>500 eV gives mn(ne)  ~ 10-11mBat ~ 1 cpd background

  13. Sensitivity Plot for CDM-WIMP direct search • Low (<10 GeV) WIMP Mass / Sub-keV Recoil Energy : • Not favored by the most-explored specific models on galactic-bound SUSY-neutralinos as CDM ; still allowed by generic SUSY • Solar-system bound WIMPs require lower recoil energy detection • Other candidates favoring low recoils exist: e.g. non-pointlike SUSY Q-balls. • Less explored experimentally

  14. ULEGe-Prototype built & studied : 5 g 10 g 4 X 5 g Segmented 180 g with dual readout

  15. R&D Program towards Realistic O(1 kg) Size Experiments (both nN & CDM) : • measure & study background at sub-keV range at KS & Y2L ; design of active & passive shielding based on this. • compare performance and devise event-ID (PSD & coincidence) strategies of various prototypes • devise calibration & efficiency evaluation schemes applicable to sub-keV range • measure quenching factor of Ge with neutron beam • study scale-up options ULEGe-detector • Keep other detector options open

  16. Yang-Yang Underground Laboratory • Operated by KIMS Collaboration, 700 m of rock overburden in east Korea • flagship program on CsI(Tl) for CDM searches • TEXONO  Install 5 g ULB-ULEGe at Y2L ; Study background and feasibility for CDM searches ; may evolve into a full-scale O(1 kg) CDM experiment Y2L

  17. Single Readout Event ID – correlate channels with different gains & shaping times e.g. 4 X 5 g Sampling of Specific Range for non-trigger-Channel 2 – i.e. look for +ve fluctuations at specific and known times Energy as defined by trigger-Channel 1 Noise Signal Ch #1 : Ch #2 :

  18. Dual Readout Event ID – correlate anode/cathodes in amplitude & timing Peak Position+Amplitue Correlations in Electrodes Calibration spectrum (55Fe) Raw/PSDs Threshold ~ 250 eV Seg. 180 g Noise Signal Cathode : Anode :

  19. KS In Situ Data - Calibration, PSD & Efficiency Evaluation • Linear 0-60 keV, better than 1% • Stability better than 5% • Threshold 220 eV at 50% efficiency by two independent methods

  20. Sub-keV Background Measurements & Comparisons 4 X 5 g (~1 yr apart) 1 kg 5 g • Similar background at KS & Y2L for same detector • Apparent difference between 5 g & 1 kg at T> 5 keV due to scaling with surface area instead, reproduced in simulations • Best Background with 4X5 g comparable to CRESST-1 • Intensive studies on background understanding under way

  21. Some first understanding on background: • Expect self-shielding effects when detector scales up from O(10 g) to O(1 kg) IFbkg is external • g-induced bkg is flat while n-induced bkgincrease with lower recoil energy.

  22. From Background to Limits: WIMP Spin-Independent Couplings : Standard conservative analysis – WIMP rates cannot be higher than total events measured

  23. WIMP Spin-dependent Couplings :

  24. Improved PSD ; dual-readout coincidence Scale up to compact 1 kg ; understand background source (g/n) ; improved shielding design AS better electronics noise levels Road Map: Threshold Vs Background

  25. Quenching Factor Measurement for Ge at CIAE’s Neutron Facilities: With 13 MV Tandem • Goals for 2008 Runs : • Use actual ULEGe 100-eV detector • Use lower energy neutron beam (860 keV50 keV) with a pulsed-LE tandem

  26. p S1 S0 Detector Scale-up Plans: • 500-g, single-element, modified coaxial HPGe design, following successful demonstration of Chicago group • Position-sensitive from drift-profile pulse shape • Dual-electrode readout and ULB specification • Delivered, being studied.

  27. 2D Projection • Another Possible Design for O(1 kg) Segmented ULEGe : • 3X3X5 elements @ 20 g each (i.e. 900 g) • Dual readout per element • veto ring  lids

  28. Summary & Outlook • An O[100 eV threshold1 kg mass1 cpd detector] has interesting applications in neutrino and dark matter physics, also in reactor monitoring • Open new detector window & detection channel : potentials for surprise • “Don’t know what to expect & what are expected” • Mass Scale-Up: recent demonstration of realistic design • Threshold– ~300 eV at hardware level; ~200 eV demonstrated with software; intensive studies under way goal: ~100 eV • Prototype data at reactor already provide competitive sensitivities for WIMP search at mass<10 GeV . • Sub-keV Background understanding and suppression – under intensive studies

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