Neutrino Physics and Dark Matter Physics with Ultra-Low-Energy Germanium Detector  Overview of TEXONO Collaboration  Kuo-Sheng Reactor Neutrino Laboratory  Results on Neutrino Magnetic Moments & status on Neutrino-Electron Elastic Scattering  Physics & Requirements for ULE-HPGe  R&D projects on ULE-HPGe Prototypes  Plans Lin, Shin-Ted/ 林欣德 On Behalf of Taiwan Experiment On NeutrinO (TEXONO) Collaboration Institute of Physics, Academia Sinica 5th Italian-Sino Workshop on Relativistic Astrophysics 

TEXONO Collaboration Collaboration : Taiwan (AS, INER, KSNPS, NTU) ; China (IHEP, CIAE, THU, NJU) ; Turkey (METU) ; India (BHU) Close Partnership with : Korea (KIMS) Program: Low Energy Neutrino & Astroparticle Physics  Kuo-Sheng (KS) Reactor Neutrino Laboratory  oscillation expts.  m  0  anomalous properties & interactions  reactor : high flux of low energy electron anti-neutrinos  physics full of surprises, need intense -source ※ study/constraint new regime wherever experimentally accessible ※ explore possible new detection channels

Kuo-Sheng Nuclear Power Plant KS NPS-II : 2 cores  2.9 GW KS Lab: 28 m from core#1

Kuo Sheng Reactor Neutrino Laboratory Configuration: Modest yet Unique Flexible Design: Allows different detectors conf. for different physics Front View (cosmic veto, shielding, control room …..)  /fission 235 U: U: Pu: Pu: 0.4 U (n,  ) 1.2 Inner Target Volume

Reactor Neutrino Spectrum  /fission 235 U: U: Pu: Pu:0.4 U (n,  ) 1.2  e ) ~ 6.4 X / sec*cm 2 Reactor Operation Data

R&D :  Coh. ( N)  T < 1 keV Results:   ( e )  T ~ keV Under Analysis  SM  ( e)  T > 3 MeV Reactor Neutrino Interaction Cross-Sections massqualityDetector requirements

KS Experiment: Period I, II, III,IV,V-I Detectors FADC Readout [16 ch., 20 MHz, 8 bit] ULB-HPGe [1 kg] CsI(Tl) Array Multi-Disks Array [few Tb*6]

8 Neutrino Electromagnetic Properties : Magnetic Moments fundamental neutrino properties & interaction ; necessary consequences of neutrino masses/ mixings Astrophysics bound on   –  B  however, model dependence Anomalous  e scattering is valid for - both Dirac/Majorana - both Diagonal/Transition   i j Minimally Extended Standard Model: However, many models can enhance it significantly ( M, W R …..)

Magnetic Moment KS   e scattering with   simple compact all-solid design : HPGe (mass 1 kg) enclosed by active NaI/CsI anti-Compton, further by passive shielding & cosmic veto  selection: single-event after cosmic-veto, anti-Comp., PSD

Data Analysis  TEXONO data  background comparable to underground CDM experiment : ~ 1 day -1 keV -1 kg -1 (cpd)  DAQ threshold 5 keV analysis threshold 12 keV  Combined all information Spectrum ; SM     i / f  Reactor On/Off Before/After cuts  e ( SM)   e  e    

11 Systematic effects Best-fit  The limit based on 570.7/127.8 days of Reactor ON/OFF:   e ) <7.4 X  B (90% PRD Results on neutrino magnetic moment

Search of  at low threshold  high signal rate & robustness: Gemma prelim. Result:   e ) <5.4 X  B (90% Neutrino radiative decay

13 e e scattering However, SM >>MM at few MeV ! The differential cross section can be represented SMMM

CsI(Tl) Array (~200 kg) :  e) Z =40 cm Single Crystal Q L Vs Q R (Raw Data) Region of Interest for SM  e) Z = 0 cm 208 Tl 40 K 137 Cs Data analysis under way.. (~40000/~12000 day-kg for ON/OFF in PII to PV)

15 Status of neutrino-electron scattering Background understanding and suppression --Multiple-hit analysis ( Cosmic ray tagged,  cascades of 208 Th ) =>  sin 2  w   more data  Global analysis of all spectra Expect:

16 “Ultra-Low-Energy” HPGe Detectors  ULEGe – developed for soft X-rays detection ; easy & inexpensive & robust operation  Prototypes built and studied :  5 Y2L  4 X 5 KS/Y2L  10 AS/CIAE  Segmented 180 KS  PC-500 g single  Physics for O[100 eV threhold  1 kg mass  1 cpd detector] :  N coherent scattering  Low-mass WIMP searches  Improve sensitivities on   [   search  ~  B ]  Implications on reactor operation monitoring  Open new detector window & detection channel available for surprises

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

18 A fundamental neutrino interaction never been experimentally-observed   ~ N 2 applicable at E 1 at 250 eV of threshold; At threshold 100 eV-> 11 count /day/ kg)  a sensitive test to Standard 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)  involves new energy range at low energy, many experimental challenges & much room to look for scientific surprises Neutrino-Nucleus Coherent Scattering

19 Characteristics of WIMP signal Scattering off nuclei A 2 dependence –coherence loss –relative rates M W relative to M N –large M W - lose mass sensitivity –if ~100 GeV Present limits on rate –WIMP mass if not too heavy different targets accelerator measurements –galactic origin annual modulation directional courtesy of Gaitskell recoil energy, E R (keV) dR/dE R from Jungman et al. Vary M W for M N =73

20 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

21  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

22 Evaluation of Selection Efficiency:  Select clean sample of physics events with cosmic-ray and anti-Compton tags  Study survival probabilities of these with the independent selection cuts on Ge-signals Good efficiency > 200 eV for low background KS data with 4X5 g

23  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 after corrections due to quenching factor  Intensive studies on background understanding under way 5 g 4 X 5 g 1 kg Sub-keV Background Measurements & Comparisons

24 Results on WIMP Spin-Independent Cross Section Limits & Sensitivities Standard conventional analysis – Maximum gap method ; Optimal Interval method

25 WIMP-neutron cross section WIMP Spin-dependent Cross Section Limits & Sensitivities Allowed regions of WIMP-nucleon couplings (proton and neutron) with a WIMP mass of 5 GeVc^-2, at 90%C.L

26 ( 10 6 evts/kg-d) WIMP scatters ( 10 6 evts/kg-d) Neutrons Slow muons Radioactive Nuclides in solids, surroundings 238 U, 232 Th chains, 40 K Airborne Radioactivity 222 Rn Radioactive Nuclides in detector, shield (especially 222 Rn daughters, including 210Pb t1/2=22 years) Radioactive Nuclides in atmosphere Cosmic Rays Gammas Electrons Fast muons Shield contaminants Backgrounds: cosmic rays and natural radioactivity courtesy of S. Kamat Neutron capture ( α, n) Muon capture Photo fission Spontaneous fission ( α, n)

27  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) :

28 Single Readout Event ID – correlate two 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 :

29 Dual Readout Event ID – correlate anode/cathodes in amplitude & timing SignalNoise Anode : Cathode : e.g. Seg. 180 g Peak Position Correlations between Electrodes

30 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 with a smaller tandem With 13 MV Tandem

31 Detector Scale-up Plans:  500-g, single-element, modified coaxial HPGe design, inspired by successful demonstration of Chicago group (nucl-ex/ )  Dual-electrode readout and ULB specification  Arrived in April S0S0 S1S1 p Most of energy deposited in the surface. A larger detector have a better  suppression.

32 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  Mass Scale-Up: recent demonstration of realistic design  Threshold – ~300 eV at hardware level, intensive studies on software techniques to aim at ~100 eV, & on their stabilities and universalities  Prototype data at reactor already provide competitive sensitivities for WIMP search at mass<10 GeV.  Sub-keV Background understanding and suppression – under intensive studies