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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 Ultra-Low Energy Germanium Detectors for Neutrino-Nucleus Coherent Scattering and Dark Matter Searches Henry T. Wong / 王子敬 Academia Sinica / 中央研究院 @ OCPA Workshop July 2008 Hong Kong
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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
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28 m from core#1 @ 2.9 GW Shallow depth : ~30 meter-water-equivalent Reactor Cycle : ~50 days OFF every 18 months Kuo Sheng Reactor Neutrino Laboratory Front Gate
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Configuration: Modest yet Unique Flexible Design: Allows different detectors conf. for different physics Inner Target Volume Front View (cosmic vetos, shieldings, control room …..)
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R&D : Coh. ( N) T < 1 keV Results : ( e ) T ~ 1-100 keV On-Going Data Taking & Analysis SM ( e) T > 2 MeV Reactor Neutrino Interaction Cross-Sections massqualityDetector requirements 1 counts / kg-keV-day
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Reactor Neutrino Spectra Evaluation… Reactor Operation Data Nuclear Physics
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Neutrino Electromagnetic Properties : Magnetic Moments e.g. requires m 0 a conceptually rich subject ; much neutrino physics & astrophysics can be explored -osc. : m , U ij 0 : m , U ij, D / M : m , U ij, D / M, fundamental neutrino properties & interaction ; necessary consequences of neutrino masses/ mixings ; in principle can differentiate Dirac/Majorana neutrinos explore roles of neutrinos in astrophysics
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Magnetic Moment Searches @ KS simple compact all-solid design : HPGe (mass 1 kg) enclosed by active NaI/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 -1 keV -1 kg -1 (cpd) DAQ threshold 5 keV analysis threshold 12 keV
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Search of at low energy high signal rate & robustness: >>SM [ decouple irreducible bkg unknown sources ] T << E d /dT depends on total flux but NOT spectral shape [ flux well known : ~6 fission- ~1.2 238 U capture- per fission ] Direct Experiments at Reactors GEMMA-07 (Ge+NaI): e ) < 5.8 X 10 -11 B KS Limit: e < 7.4 X 10 -11 B @ 90% CL
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“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 Goal O[100 eV threhold 1 kg mass 1 cpd detector] physics : N coherent scattering Low-mass WIMP searches Improve sensitivities on Implications on reactor operation monitoring Open new detector window & detection channel available for surprises
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a fundamental neutrino interaction never been experimentally- observed ~N 2 applicable at E <50 MeV where q 2 r 2 <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 Standard Model Cross-Sections: Neutrino-Nucleus Coherent Scattering :
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Expected Interaction Rates at KS @ different Quenching Factors by-product : T>500 eV gives e ) ~ 10 -11 B at ~ 1 cpd background e.g. at QF=0.25 & 100 eV threshold Rate ~ 11 kg -1 day -1 @ KS c.f. N (Ge;1 keV) @ accelerator ~ 0.1 kg -1 day -1 ; ne-p (water) @ KS ~ 1 kg -1 day -1
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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
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ULEGe-Prototype built & studied : 5 g 10 g 4 X 5 g Segmented 180 g with dual readout
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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 R&D Program towards Realistic O(1 kg) Size Experiments (both N & CDM) :
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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 Yang-Yang Underground Laboratory Y2L
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Single Readout Event ID – correlate channels with different gains & shaping times e.g. Energy as defined by trigger-Channel 1 Sampling of Specific Range for non-trigger- Channel 2 – i.e. look for +ve fluctuations at specific and known times 4 X 5 g Signal Noise Ch #1 : Ch #2 :
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Dual Readout Event ID – correlate anode/cathodes in amplitude & timing SignalNoise Anode : Cathode : Peak Position+Amplitue Correlations in Electrodes Threshold ~ 250 eV Seg. 180 g Calibration spectrum ( 55 Fe) Raw/PSDs
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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
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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 5 g 4 X 5 g (~1 yr apart) 1 kg Sub-keV Background Measurements & Comparisons
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Some first understanding on background: Expect self-shielding effects when detector scales up from O(10 g) to O(1 kg) IF bkg is external -induced bkg is flat while n- induced bkg increase with lower recoil energy.
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From Background to Limits: WIMP Spin-Independent Couplings : Standard conservative analysis – WIMP rates cannot be higher than total events measured
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WIMP Spin-dependent Couplings :
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Road Map: Threshold Vs Background AS better electronics noise levels Scale up to compact 1 kg ; understand background source ( /n) ; improved shielding design Improved PSD ; dual-readout coincidence
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Quenching Factor Measurement for Ge at CIAE’s Neutron Facilities: Goals for 2008 Runs : Use actual ULEGe 100-eV detector Use lower energy neutron beam (860 keV 50 keV) with a pulsed-LE tandem With 13 MV Tandem
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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. SS SS p
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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 2D Projection
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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 Summary & Outlook
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