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 CollaborationCollaboration : 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. m0 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

235U: 3.4 238U: 0.5 239Pu: 1.8 241Pu: 0.4 U (n,) 1.2

Inner Target Volume

Reactor Neutrino Spectrum

/fission

235U:3.4 238U:0.5 239Pu:1.8 241Pu:0.4 U (n,) 1.2

e) ~ 6.4X1012 / sec*cm2

Reactor Operation Data

R&D : Coh. (N)

T < 1 keV Results: (e)

T ~ 1-100 keV

Under Analysis SM (e)

T > 3 MeV

Reactor Neutrino Interaction Cross-Sections

massquality Detector 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]

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Neutrino Electromagnetic Properties : Magnetic Moments

• fundamental neutrino properties & interaction ; necessary consequences of neutrino masses/ mixings

• Astrophysics bound on

10-10 – 10-12 Bhowever, 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, WR …..)

Magnetic Moment Searches @ 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

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11)(2

ETmedT

de

Data Analysis

TEXONO data

background comparable to underground CDM experiment : ~ 1 day-1keV-1kg-1 (cpd)

DAQ threshold 5 keV analysis threshold 12 keV

Combined all information

i

f

i

f

ff

Spectrum ;

SM

i / f i / f

Reactor On/Off

Before/After cuts

e (SM) e e

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• Systematic effects

• Best-fit

The limit based on 570.7/127.8 days of Reactor ON/OFF: e) <7.4 X 10-11 B (90% CL) @ PRD 75 2007

Results on neutrino magnetic moment

Search of at low threshold high signal rate & robustness:

Gemma prelim. Result:e) <5.4 X 10-11 B (90% CL) @hep-ex0705.4576v1

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11)(2

ETmedT

de

Neutrino radiative decay

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ee scattering

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

SM MM

CsI(Tl) Array (~200 kg) : e)

Z =40 cm

Single Crystal QL Vs QR

(Raw Data)

Region of Interest for SM e)

Z = 0 cm

208Tl

40K 137Cs

Data analysis under way ..

(~40000/~12000 day-kg for ON/OFF in PII to PV)

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Status of neutrino-electron scattering

Background understanding

and suppression

--Multiple-hit analysis (Cosmic ray tagged, cascades of 208Th )

=>sin2w

more data

Global analysis of all spectra

Expect:

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“Ultra-Low-Energy” HPGe Detectors ULEGe – developed for soft X-rays detection ; easy & inexpensiv

e & robust operation Prototypes built and studied :

5 g @ Y2L 4 X 5 g @ KS/Y2L 10 g @ AS/CIAE Segmented 180 g @ KS PC-500 g single element @AS

Physics for O[100 eV threhold1 kg mass1 cpd detector] :

N coherent scattering Low-mass WIMP searches Improve sensitivities on [ search ~10-11 B ] Implications on reactor operation monitoring Open new detector window & detection channel available

for surprises

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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

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A fundamental neutrino interaction never been experimentally-observed

~N2 applicable at E<50 MeV ( Take Q.F. =0.25, S/N >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

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Characteristics of WIMP signal

• Scattering off nuclei• A2 dependence

– coherence loss– relative rates

• MW relative to MN

– large MW - 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

cour

tesy

of G

aits

kell

recoil energy, ER (keV)

dR/d

E R

from

Jun

gman

et a

l.Vary MW for MN=73

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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-neu

tralinos 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

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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

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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

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Similar background at KS & Y2L for same detector Apparent difference between 5 g & 1 kg at T> 5 keV due to scaling with surfa

ce area instead, reproduced in simulations Best Background with 4X5 g comparable to CRESST-1 after corrections due t

o quenching factor Intensive studies on background understanding under way

5 g

4 X 5 g

1 kg

Sub-keV Background Measurements & Comparisons

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Results on WIMP Spin-Independent Cross Section

Limits & Sensitivities

Standard conventional analysis – Maximum gap method ;

Optimal Interval method

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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

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WIMP scatters (< 1 evts /10 kg/ day)(< 1 evts /10 kg/ day) swamped by backgrounds ( > 10 ( > 106 6 evts/kg-d)evts/kg-d)

NeutronsNeutrons

Slow muons

Radioactive Nuclides in solids,surroundings 238U, 232Th chains, 40K

AirborneRadioactivity222Rn

Radioactive Nuclidesin detector, shield(especially 222Rn

daughters, including 210Pb t1/2=22 years)

Radioactive Nuclides

in atmosphere

Cosmic Rays

GammasGammas

ElectronsElectrons

Fast muonsFast muons

Shieldcontaminants

Backgrounds: cosmic rays and natural radioactivity

courtesy of S. Kamat

Neutron capture (α, n)

Muon capture Photo fission

Spontaneous fission

(α, n)

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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) :

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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 :

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

Signal

Noise

Anode :

Cathode :

e.g.

Seg. 180 g

Peak Position Correlations between Electrodes

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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

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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

Arrived in April 2008 @AS.

S0

S1

p

Most of energy deposited in the surface. A larger detector have a better suppression .

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Summary & Outlook

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 softwa

re 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