Limits on Low-Mass WIMP Dark Matter with an Ultra-Low-Energy Germanium Detector at 220 eV Threshold Overview (Collaboration; Program; Laboratory) Physics Motivations & Detector Requirements Dark Matter Analysis & Results [PRD 79(R), 2009] Status & Plans Muhammed Deniz on behalf of TEXONO Collaboration Academia Sinica /TAIWAN METU/TURKEY

TEXONO Collaboration & Physics Program 2/14 Limits on Low-Mass WIMP Dark Matter Taiwan EXperiment On NeutrinO

Kou-Sheng Reactor Power Plant 3/14 Limits on Low-Mass WIMP Dark Matter

Laboratory & Inner Target Volume ULE-Ge surrounded by active NaI/CsI anti-Compton detectors  cosmic ray veto pannels  passive shielding 4/14 Limits on Low-Mass WIMP Dark Matter

Spin-Independent 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  Various gravitational effects favor lower recoil energy  Solar-system bound WIMPs; Dark Disk etc.  Some theoretical scenarios favor lower recoils  e.g. non-pointlike SUSY Q-balls; SM+scalar; axion-like models etc.  Less explored experimentally  better detector technology & background control. ~2006 Sensitivity Plot for Direct WIMP Search 5/14 Limits on Low-Mass WIMP Dark Matter

 ULE-HP Ge: developed for soft X-rays detection; easy & inexpensive & robust operation  Various Prototypes (5-500 g) built and studied:  This Analysis : 4 x 5g; 0.34 kg*day live time  Physics for O [100 eV threshold  1 kg mass  1 cpd/kg/keV detector]:  N coherent scattering  Low-mass WIMP searches  This Talk  Improve sensitivities on neutrino magnetic moments  Implications on reactor operation monitoring  Open new detector window & detection channel available for surprises Ultra-Low Energy HP-Ge Detectors 6/14 Limits on Low-Mass WIMP Dark Matter

 DAQ threshold at ~ 4.3  above mean of noise fluctuations  minimal DAQ dead time  Max. amplitude of physics events  good margins above threshold  Efficiency Evaluation  from ( mean, RMS ) of Max. Amplitude distribution of physics events. Candidate Events: selected by Anti-Compton [ACV :  ]  Cosmic-Ray [CRV:  ] Vetos  Pulse-Shape Discrimination [PSD: electronic noise] Critical Issues: Signal efficiencies for trigger, DAQ & Selection Non-Ge Efficiency [DAQ,ACV,CRV] : evaluated by Random Trigger events. Evaluation of Trigger Efficiency 7/14 Limits on Low-Mass WIMP Dark Matter

Noise  correlations in two readout of different gains & shaping times Specific Range of shaping time -- look for pulse fluctuations at specific and known times Energy defined by integration Signal PSD Selection: Suppress Electronic Noise 6s6s 12  s 8/14 Limits on Low-Mass WIMP Dark Matter

 PSD  = 220 eV Supported & statistics reinforced by 55 Fe calibration spectra  deviations from flat spectrum at low energy Physics events with CRV & ACV Tags  Survival Probabilities 55 Fe sources for calibration & PSD efficiency 55 Fe sources for calibration & PSD efficiency Noise edge ~ 300 eV PSD Selection Efficiency 9/14 Limits on Low-Mass WIMP Dark Matter PSD

Event kg -1 keV -1 day -1 E ( keV ) ULE-Ge (5g × KS GS HP-Ge (1 KS  Bkg ~ O (1 cpd/kg/keV )>10 keV, ~ to underground experiments.  ULE-Ge KS ~ GranSasso  Intensive studies on sub-keV background understanding Background Measurement & Comparisons 10/14 Limits on Low-Mass WIMP Dark Matter

 Standard conservative analysis  WIMP rates cannot be larger than total events measured [NO BACKGROUND SUBTRACTION]  Standard astrophysics parameters  Optimal Interval Method [Yellin PRD 2002]  Standard conservative analysis  WIMP rates cannot be larger than total events measured [NO BACKGROUND SUBTRACTION]  Standard astrophysics parameters  Optimal Interval Method [Yellin PRD 2002] neutron-induced background free The sensitivity: defining bins Quenching Factor Energy (eV) Raw Counts Background after CRV-ACV-PSD Net Efficiencies of signals Spin-independent Cross Section (cm 2 ) Limit at 90% C.L. 0.99x at 5 GeV 2.1x at 50 GeV 2.9x at 5 GeV 6.5x at 50 GeV Spin-dependent Cross Section (cm 2 ) Limit at 90% C.L. ~1 WIMP Spin-Independent Cross Section 11/14 Limits on Low-Mass WIMP Dark Matter

Formalisms [Tovey et al., PLB 2000] Ge matrix elements [Dimitrov et al., PRD 1995] Allowed regions of WIMP-nucleon couplings (proton and neutron) for WIMP mass of 5 GeV, at 90% C.L WIMP-Neutron Spin-dependent Cross Section 12/14 Limits on Low-Mass WIMP Dark Matter The isotopes of 73 Ge abundances ~8% provides additional probe to the spin-dependent couplings of WIMP due to unpaired neutron

From By-Product Physics to Dedicated Experiment:  Duplicate Experiment at “JinPing-Deep Underground Lab in SiChuan-China”  20 g ULE-Ge 2010; 500 g PC-Ge 2011  Tallest Peak 4193 m  Max. Rock Overburden: 2375 m  Road Tunnel Distance: 17.5 km 13/14 Limits on Low-Mass WIMP Dark Matter Hydroelectric Power Plant Hydroelectric Power Plant

Competitive limits at WIMP-mass of < 10 GeV obtained with 20 g ULE-Ge prototype at a shallow depth reactor laboratory, for both spin-independent and spin-dependent couplings; Studies on background understanding & suppression at sub-keV range; Data taking at KS with a 500-g Point-Contact Ge; construction of 900-g PC-Ge planning for next year; Evolving to dedicated dark matter searches at new deep underground laboratory at Sichuan ~2010. Goals : open new detection channel and detector window for neutrino and dark matter physics available for surprises Status and Plans 14/14 Limits on Low-Mass WIMP Dark Matter