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