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Ultra-Low-Energy HPGe Detector for WIMP Searches. Starting Points (Collaboration ; Laboratories ; Research Program) Physics & Requirements for ULE-HPGe - focus on WIMP Searches R&D on ULE-HPGe Prototypes Status & Plans. Henry T. Wong / 王子敬 Academia Sinica / 中央研究院. @. - PowerPoint PPT Presentation
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Starting Points (Collaboration ; Laboratories ; Research Program)
Physics & Requirements for ULE-HPGe - focus on WIMP Searches
R&D on ULE-HPGe Prototypes Status & Plans
Ultra-Low-Energy HPGe Detector for WIMP Searches
@
Henry T. Wong /王子敬Academia Sinica /中央研
究院
TEXONO Collaboration
Collaboration : Taiwan (AS, INER, KSNPS, NTU) ; China (IHEP, CIAE, THU, NKU, NJU) ; Turkey (METU) ; India (BHU)
Close Partnership with : Korea (KIMS)
Facilities : Kuo-Sheng Reactor Lab (Taiwan) ; Yang-Yang Underground Lab (Korea) ; CIAE Neutron Beam (China)
Program : Low Energy Neutrino & Astroparticle Physics
Goals : Develop O[100 eV threhold1 kg mass1 cpd detector] for neutrino physics and dark matter searches
Kuo Sheng Reactor Neutrino Laboratory :
NPS-IV
28 m from core#1 @ 2.9 GW Different detectors for different physics
R&D : Coh. (N)
T < 1 keV Completed Results :(e) : T~1-100 keV [Lin ST’s talk]
Axions : T ~ keV-MeV [Chang HM’s talk ]
On-Going Data Taking & Analysis SM (e)
T > 2 MeV
Reactor Neutrino Interaction Cross-Sections
massquality Detector requirements
1 counts / kg-keV-day
Threshold ~ 100 eV
Operated by KIMS Collaboration, 700 m of rock overburden in east Korea
flagship program on CsI(Tl) for CDM searches [SK Kim’s talk]
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
“Ultra-Low-Energy” HPGe Detectors ULEGe – developed for soft X-rays detection ; easy & inexp
ensive & robust operation Prototypes built and studied :
5 g @ Y2L 4 X 5 g @ KS/Y2L 10 g @ AS/CIAE segmented 180 g @ AS/KS
Being built : 500 g single element Physics for O[100 eV threhold1 kg mass1 cpd dete
ctor] : N coherent scattering Low-mass WIMP searches This Talk Improve sensitivities on Implications on reactor operation monitoring Open new detector window & detection channel avai
lable for surprises
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-boun
d 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 & being studied :
5 g 10 g 4 X 5 g
Signal side
High Voltage side
A B
AB view
A B
43mm
43m
m10 m
m
20mm
20m
m
S3
S1
S2
S4
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) :
A PSD Scheme to differentiate Physics Vs Noise Events
Calibrations by keV lines & “0” from random trigger Achieved threshold < 100 eV with Fe55 source : lowest for bu
lk radiation detectors ! Threshold depends on background level
PSD Cut Threshold ~ 100 eV
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
NoiseCh #1 :
Ch #2 :
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
Dual Readout Event ID – correlate anode/cathodes in amplitude & timing
Signal
Noise
Anode :
Cathode :
e.g.
Seg. 180 g
Peak Position Correlations between Electrodes
Similar background at KS & Y2L for same detector Apparent difference between 5 g & 1 kg at T> 5 keV due to sca
ling with surface area instead, reproduced in simulations Best Background with 4X5 g comparable to CRESST-1 after co
rrections due to quenching factor Intensive studies on background understanding under way
5 g
4 X 5 g
1 kg
Sub-keV Background Measurements & Comparisons
WIMP Spin-Independent Couplings : Limits & Sensitivities
Standard conservative analysis – WIMP rates cannot be higher than total events measured
Quenching Factor Measurement for Ge at CIAE’s Neutron Facilities:
Goals for Oct 07 Runs : Use actual ULEGe 100-eV detector Use lower energy neutron beam wit
h a smaller tandem
With 13 MV Tandem
Detector Scale-up Plans:
500-g, single-element, modified coaxial HPGe design, inspired by successful demonstration of Chicago group (nucl-ex/0701012)
Dual-electrode readout and ULB specification Being built, available first-half 2008.
S0S1
p
Summary & Outlook (Score Card)
An O[100 eV threshold1 kg mass1 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