 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: )  Status & Plans Ultra-Low Energy Germanium Detectors for Neutrino-Nucleus Coherent Scattering and Dark Matter Searches Henry T. Wong / 王子敬 Academia Sinica / OCPA Workshop July 2008 Hong Kong

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

 28 m from 2.9 GW  Shallow depth : ~30 meter-water-equivalent  Reactor Cycle : ~50 days OFF every 18 months Kuo Sheng Reactor Neutrino Laboratory Front Gate

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

R&D :  Coh. ( N)  T < 1 keV Results :   ( e )  T ~ keV On-Going Data Taking & Analysis  SM  ( e)  T > 2 MeV Reactor Neutrino Interaction Cross-Sections massqualityDetector requirements 1 counts / kg-keV-day

Reactor Neutrino Spectra Evaluation… Reactor Operation Data Nuclear Physics

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

Magnetic Moment 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

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-  ~ U capture- per fission ] Direct Experiments at Reactors    GEMMA-07 (Ge+NaI):   e ) < 5.8 X  B KS Limit:   e  < 7.4 X  90% CL

“Ultra-Low-Energy” HPGe Detectors  ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation  Prototypes built and studied (starting 2003) :  5 Y2L  4 X 5 KS/Y2L  10 AS/CIAE  segmented 180 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

 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 :

Expected Interaction Rates at different Quenching Factors by-product : T>500 eV gives   e )  ~  B at ~ 1 cpd background e.g. at QF=0.25 & 100 eV threshold Rate ~ 11 kg -1 day KS c.f. N (Ge;1 accelerator ~ 0.1 kg -1 day -1 ; ne-p KS ~ 1 kg -1 day -1

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

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

 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) :

 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

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 :

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

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

 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

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.

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

WIMP Spin-dependent Couplings :

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

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

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. SS SS p

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

 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