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:0712.1645)

Status & Plans

Ultra-Low Energy Germanium Detectors for Neutrino-Nucleus Coherent Scattering and Dark

Matter Searches

Henry T. Wong /王子敬Academia Sinica /中央

研究院@

OCPA WorkshopJuly 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 core#1 @ 2.9 GWShallow depth : ~30 meter-water-equivalentReactor 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 ~ 1-100 keV

On-Going Data Taking & Analysis SM (e)

T > 2 MeV

Reactor Neutrino Interaction Cross-Sections

massquality Detector requirements

1 counts / kg-keV-day

Reactor Neutrino Spectra Evaluation…

Reactor Operation Data

Nuclear Physics

e

Neutrino Electromagnetic Properties : Magnetic Moments

e.g.

requires m0

a conceptually rich subject ; much neutrino physics & astrophysics can be explored

-osc. : m, Uij

0: m, Uij , D/M

: m, Uij , 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 Searches @ 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-1keV-1kg-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- ~1.2 238U capture-per fission ]

22

11)(2

ETmedT

de

Direct Experiments at Reactors

GEMMA-07 (Ge+NaI): e) < 5.8 X 10-11 B

KS Limit:

e < 7.4 X 10-11 B

@ 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 g @ Y2L 4 X 5 g @ KS/Y2L 10 g @ AS/CIAE segmented 180 g @ AS/KS

Built & being studied : 500 g single element Goal O[100 eV threhold1 kg mass1 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

~N2 applicable at E<50 MeV where q2r2<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 KS @ different Quenching Factors

by-product : T>500 eV gives

e) ~ 10-11 B at ~ 1 cpd background

e.g. at QF=0.25 & 100 eV threshold Rate ~ 11 kg-1 day-1 @ KS

c.f. N (Ge;1 keV) @ accelerator ~ 0.1 kg-1 day-

1 ; ne-p (water) @ KS ~ 1 kg-1 day-1

e

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

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

S1

S2

S3

Input stage location of the preamplifier

CrystalHolder

Crystal

ENDCAPDiameter :

<85mm

DETECTOR VIEW INSIDE ENDCAP AND INPUT STAGE LOCATIONS

Cooling finger

S4

Copper shielding to be defined

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

NoiseCh

#1 :

Ch #2 :

Dual Readout Event ID – correlate anode/cathodes in amplitude & timing

Signal

Noise

Anode :

Cathode :

Peak Position+Amplitue Correlations in Electrodes

Threshold ~ 250 eV

Seg. 180 g

Calibration spectrum (55Fe) 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 keV50 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.

SS

p

Another Possible Design for O(1 kg) Segmented ULEGe :

※3X3X5 elements @ 20 g each (i.e. 900 g)

※Dual readout per element

※veto ring lids2D Projection

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

“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