Low Energy Neutrino Low Energy Neutrino and Dark Matter Physics with and Dark Matter Physics with

Germanium DetectorsGermanium DetectorsLi Hau-Bin (Li Hau-Bin (on behalf of TEXONO Collaboration)on behalf of TEXONO Collaboration)Academia SinicaAcademia Sinica

● Overview :Kuo-Sheng Reactor Neutrino Laboratory (KSNL)● Germanium detectors● Neutrino programs at KSNL● Dark Matter searches at KSNL

and China Jin-Ping Underground Laboratory (CJPL) ● Summary

2017 May 16

TEXONO CollaborationTEXONO Taiwan EXperiment On NeutrinO (since 1997)

Neutrino Physics at Kuo-Sheng Reactor Neutrino Laboratory (KSNL)● Taiwan (AS, INER, KSNPS) ● Turkey (METU, DEU) ● India (BHU)

22

Kuo Sheng Reactor Neutrino Laboratory

● 2 reactor core, 2 GW.● Lab. : 28 m from nearest core.● 30mwe concrete over burden.

33

Kuo Sheng Reactor Neutrino Laboratory

Flexible Design: Allows different detectors conf. for different physics

44

Kuo Sheng Reactor Neutrino Laboratory

55

● Active cosmic shielding with plastic scintillator.● NaI(Tl) as anti-Compton detector.● Flexible design.

Ge detector● Neutrino physics at sub-keV :

neutrino magnetic-moment,

νN-coherent scattering, reactor-monitoring.● Low-mass ( ~10 Gev) WIMP Search. ● Allow Low Threshold Measurements(~100eV).● However, no γ/nuclei recoil separation.

66

lower thresholdlower threshold

low

er backg

rou

nd

low

er backg

rou

nd

Various Ge detectorsp- PCGe

[~ 1 kg]

p+

n+(~1mm Li diffused)

4x5g ULEGe

n- PCGe[500 g]

n+

p+(~0.5 μm Boron implanted) 500 g

p-PCGe : ~kg, threshold ~300 eVwith bulk/surface feature

n-PCGe : ~kg, threshold ~300 eVwithout bulk/surface feature

ULEGe : ~g, threshold ~100 eV

77

Physics goals/challenge for sub-keV Ge Detectors

mass ~1kg : threshold ~few✕100 eV : bgk ~few cpkkd● Quenching Factors.● Energy Definition & Calibration.● Trigger Efficiencies near threshold.● Physics vs. Noise Pulse-Shape Selection : algorithms & efficiencies.

● Bulk vs. Surface Events Selection : algorithms & efficiencies.

● Background understanding

88

Quenching FactorQuenching Factor

Trigger, various efficienciesTrigger, various efficiencies

Challenge for sub-keV Ge

99

deviate from linearity deviate from linearity of pulse-amplitude of pulse-amplitude

● Quenching factor at sub-keV are not well known.● Energy and efficiencies should be measured/defined

carefully at sub-keV range.● non-linearity had been checked.

310

eV

370

eVpulse-amp. in unit of noise RMS

a bless (most background are surface) and a curse,need to know (at low E):

● efficiency ε● leakage 1-λ

Bulk/Surface

N-type detector(submicron inactive surface layer)do not show these anomalous surface events

risetime vs. energyP-type detector

1010

surface● partial energy deposit● diffuse and drift → slow

bulk● full energy deposit● drift → fast

Neutrino interaction with electrons

non-standard model termwhen transfer energy < binding energy

of e- , :MCRRPA: Multi Configuration Relativistic Random Phase Approximation

• MCRRPA describes well Ge response function up to 80 eV

• Above 80eV Ge-crystal can treated as atom-like

• Below 80eV condense state should considered.

• Above 80 eV, error < 5 %

Phys. Rev. D  91, 013005, 2015.

Ge photo Absorption

high energy :

1111

SM : NSI/BSMν

e-e- scattering with 200 kg CsI

[PRD10,PRD10,PRD12]

Neutrino Magnetic Moment1 kg HPGe[PRL03,PRD05,PRD07]

Neutrino milli-chargesub-keV ULEGe, PCGe[PRD14]

ν-Nuclei Coherent Scattering [goal]sub-keV ULGe, PCGe Dark Matter Searches at KSNL [PRD09,PRL13,AP14] CDEX at CJPL [PRD13,PRD14,PRD14]

TEXONO Physics Program :various neutrino spectrum by Ge detector

1212

1313

Neutrino magnetic moment

Best-fit 2σ band

+ (dσ/dT)mm ~ 1/T – 1/Eν

Eν (keV)

T

ON-OFF data

minimize effect of uncertainties of E

ν

when look at low T

Neutrino milli-chargefree electron : Atomic Ionization Differential Cross-Section

with full atomic physics many-body “MCRRPA” calculationenhancement at sub-keV

best-fit results on 0.5 kg PCGethreshold = 300 eV

→ δQ < 2.1 x 10-12e at 90 % C. L.

● positive signals : known K/L ratio(different from cosmic-activationelectron-capture background)

● goal δQ ~ 10-14e at 100 eV threshold

1414

Sterile Neutrino Magnetic MomentIn Radiative Decay

Under the assumption of sterile neutrino as cold dark matter, following parameters are adopted, Dark matter density = 0.4 GeVcm-3 , Maxwellian velocity distribution with mean velocity = 220.0 km/s and Vesc = 533 km/s

Phys. Rev. D  93, 093012, 2016.

1515

νN coherent scattering● ν+A→ν+A : Never been experimental observed.

●

● Neutral current process.

● σ ∝ N2 for Eν<50MeV (Coherent)

● sensitive probe for BSM ● reactor monitoring● important process in stellar

collapse & supernova explosion

● for reactor neutrino on Ge, Tmax ~ 2 keV

Tmax ~ 500 eV after Q. F. ~ 0.21616

ν

ν

νN coherent scatteringPartial coherency, the relative change in cross sectionThe cross-section ratio between A and neutron is :

1818

νN coherent scatteringC

ou

nt

day

-1

kg

-1

keV

-1

current sensitivities

backgroundunderstanding

physics/noiseunderstanding

integral events rate(with energy resolution) :6.6 count day-1 kg-1 at 100 eV threshold0.59 count day-1 kg-1 at 200 eV threshold

estimated events rate at KSNL

Partner : CDEX Collaboration

CDEX China Dark Matter Experiment (birth 2009) Dark Matter Searches at China Jin-Ping Underground Laboratory (CJPL)

● China (THU, CIAE, NKU, SCU,YLJHD)

● Ge as primary detector.● same detector technique, i. e. bulk/surface seperation,

phys/noise seperation.

1919

China Jin-Ping Underground Laboratory (CJPL) 中國四川錦屏

● 2400+ m rock overburden, drive-in road tunnel access● 6x6x40 m cavern ready [THU & EHDC]● Deepest Underground Lab.

2400m2400m

8750m8750m

Hall AHall A

6x6x40m6x6x40m

2020

Cosmic flux at CJPL

● 61.7 ± 11.7 /(m2∙yr) [~8000/(m2∙yr) at Gran Sasso,

~950 /(m2∙yr) at Homestake]

ref : arXiv:1305.0899

● Consistent with expectation : ≈ 2.0 ± 0.4 x 10-

10cm-2s-1

≈ 10-8 of ground level2121

(Unit : Bq/kg) K-40 Ra-226(609keV)

Th-232(911keV)

Rock Sample < 1.1 1.8±0.2 < 0.27

Ground Level ( Beijing ) ~600 ~25 ~50

CJPL lab.

CDEX & CJPL-I

CDEX-1 experiment Low background facility

CDEX

LBFPandaX

PandaX

CDEX-1 Dark Matter Search

335 kg-days of data Baseline design with NaI(Tl) Fiducial mass : 915 g, Analysis threshold ~ 475 eVQ.F. adopted by TRIM software with 10% systematic uncertainty

[ PRD 93 092003 (2016) ; PRD(R) 90 091701(2014) ; PRD 90 032003 (2014) ; PRD 88 052004 (2013) ]

CDEX-1 Axion : preliminary resultsM1 transition from 57Fe from Sun [axion-nucleons]

Compton, bremsstrahlung and axion-RD (recombination & de-excitaion) [axion-electron]

Competitive results below the axion mass of 1 keV.

Phys. Rev. D  95, 052006, 2017.

galatical axion

CDEX-1 : status & plansDM resultsaxion resultsnew B/S methoddead layerDM annual modulationbackground : experiment and simulation

homemade Ge crystal, detector fabricationtransportation of Ge (cosmic-ray environment)low background electronicshomemade Cu material (underground)liquid-N for shielding and cooling

Bulk/Surface separation : a better way

using bulk-ratio and surface ratio to solve the distribution :

27

Ge Crystal Growth Facilities at THU

Ge Detector Fabrication at THU

main considerations : cost and cosmic activation

CDEX-10 Array detectors

Inner copper tankcap

PCGe

~9 kg of PCGe＆

1.5 T of LN/LAr

• Test of cryogenic system has been done and shipped to CJPL in March 2016.

• A germanium array with LN in cryogenic system is commissioning.

• The performance of LAr is under study.

3 kg + 3 kg prototype: ready to take data, threshold < 300 eV

CDEX-1t at CJPL-II

Experimental Pit

Experimental Hall

• Best sensitive in the raBest sensitive in the range of nge of

10GeV,10GeV, ~10~10 -44-44cmcm22

• 7676Ge double beta decayGe double beta decay research research

CJPL-I CJPL-II

Rock Work 4100 m3 210000+151000m3

Electric Power 70x2 kVA 10x2 MVA

Fresh Air 2400 m3/h 15000x3 m3/h

CJPL-II : construction

summary

3333

● Results on neutrino electromagnetic properties.● Competitive results on light WIMPs with sub-keV Ge,

even at a surface KSNL(same hardware underground gain x10 sensitivities)

● CDEX-1 Axion results (competitive at sub-keV mass)● Establish B/S calibration schemes.

ongoing :● Backgrond understanding.● Detector properties near noise edge.● Goal : νN coherent scattering,

~100 eV threshold & ~ cpkkd

CDEX idea• 自行研制 10kg 高纯锗探测器阵列，降低三种本底来源 :

– 前端电子学、电缆、结构材料本底优化； ( 探测器、前端电子学、超高纯无氧铜、探测器模拟、低本底测量等 ) （可以采用现有晶体、 10X 晶体等开展前期研究）

指标： 1cpkkd 0.1cpkkd @ 20keV ；

– 非锗宇生放射性同位素 (H-3, Zn-65 等 ) ；（商业公司探测器制作、运输、自行组装测试、实验等）

指标： 3cpkkd 0.1cpkkd @ 3-5keV ；

– 宇生放射性同位素： Ge-68(Ga-68) ；（俄罗斯二氧化锗 -76购置、锗金属还原、锗金属运输到美国、……）

指标： 8cpkkd 0.1cpkkd @ 1.3keV 。