On sub-keV Ge detectors and CDEX dark On sub...
Transcript of On sub-keV Ge detectors and CDEX dark On sub...
On sub-keV Ge detectors and CDEX dark matter searches
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Shin Ted Lin / Sichuan University for the CDEX Collaboration
EDU meeting @ Quy Nhon, VietnamJuly 28, 2017
On sub-keV Ge detectors and CDEX dark matter searches
Shin Ted Lin / Sichuan University , Chinafor the CDEX Collaboration
EDU meeting @ ICISE, Quy Nhon, Vietnam. July 27, 2017
OUTLINE
CDEX Collaboration
Programs : CDEX-1, CDEX-10, CDEX-10X, …
Results from CDEX-1 (Dark matter & Axions )
R&D on key Ge technologies
Outlook & Prospects
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Detection of dark matter with a point-contact germanium(PCGe) array
• Tsinghua University
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China Dark matter EXperiment (CDEX) - EST in 2009
• Sichuan University
• NankaiUniversity
• China Institute of Atomic Energy, CIAE
• Yalong River company (former:EHDC)
• Intensively collaborate with TEXONO group.
CDEX stages
• CDEX-1: Develop a large-mass PCGedetector prototype, data analysis methods, and its background understanding and suppression; since 2011.
• CDEX-10: Performances of a HPGearray detector system and its passive/ active shielding systems; since 2015.
• CDEX-10X: Fabrication of HPGe, Ge crystal growth, VFE and ULB-Cu; since 2016
• ……
• CDEX-1T: Multi-purpose experiment for dark matter and double beta decay.
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CDEX at China JinPing Underground Laboratory
CJPL: The deepest operation Underground Laboratory, located in Sichuan, China.
A new development of CJPL.
See Porf. Henry Wong’s talk July 28 . 5
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The space allocation of CJPL-I
Traffic Tunnel
LBF
CDEX
PandaX
Total space: 4000 m3
Lab Space: 6.5m(W) x6.5m(H) x 42m(L)
CDEX CJPL-LBF PandaX
9 km Ventilation system
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4*5g ULEGe
1kg pPCGe
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Detectors in CDEX -0/1
20 cm PE (B)
1 m PE20 cm Pb
>20 cm OFHC
1 kg-scale pPCGe : low energy threshold & good energy resolution.
NaI, enclosed the cryostat of Ge, served as anti-Compton detector.
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Abnormal surface signal of pPCGe
1kg pPCGe @ CJPL
n+ “inactive layer” is not totally dead; signals finite but slower rise time
Algorithm
Measure energy-dependent signal-retaining (eBS) & background-suppressing (lBS) efficiencies through at least two calibration data & solving the coupled equations.
The new promising analysis is established together with TEXONO group.
CDEX-1A
• C1A 1kg-PPCGe + NaI(Tl)
• Bulk/Surf Discrimination
Q.Yue et al., PRD 90(RC) 091701,2014
B/S disc. to get rid of the Surface events with slow rise-time and partial charge collection;
1/3 background lower with/without AC detector; The best sensitivity by PCGe and Exclude the regions
favored by CoGeNT.
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CDEX-1A 2016: Results of Light WIMPs Searches
Reference: PRD 93 092003 (2016) ; PRD(R) 90 091701(2014) ;
PRD 90 032003 (2014) ; PRD 88 052004 (2013)
Configurations:*335 kg-days of data @ CJPL (2016)*Baseline design with NaI(Tl) *Fiducial mass : 915 g *Analysis above : 475 eV*Q.F. adopted by TRIM software with 10% systematic uncertainty
~2 times more sensitive than 2014 SI & SD results AM analysis with >1+1 year data going on.
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CDEX-1A : Axion searches
M1 transition from 57Fe from Sun [axion-nucleons]
Compton, bremsstrahlung and axio-RD (recombination & de-excitaion) [axion-electron]
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CDEX-1A : Axion searches
Reference: Majorana demonstrator PRL 2017
S. Liu et al.(CDEX Collaboration), PRD 2017
Formula reference: Pospelov et al. PR D 78, 115012 (2008)
Competitive results below the axion mass of 1 keV.
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CDEX-10 : An array detector
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.
PCGe
~9 Kg of PCGe⊕
1.5 Ton of LN/LAr
TargetLN
Inner copper tankcap
Totally 10kg PPCGe under testing and run at CJPL!
Background control on CDEX-10X
• Cosmogenic Backgrounds/ Natural background sources/ Detector responses:
– The rate decreases with energy continuously from sub-keV to 20keV;
– CDEX PCGe: 68Ga ~ 1cpkd; Background Level: ~1cpkkd @ 20keV;
Shorten the Ge crystal and detector fabrication time to less than 0.5 year to lower the 3H continue background: 18 cpkd?? 1 cpkd;
Enrichment (76Ge) and/or UG Ge crystal growth + detector fabrication to lower the Ge-68 0.1cpkkd、 Reduce of 3H concentration further.
LB-VFE & ULB-Copper & A cylinder tank with 14 meter diameter: 1 0.1 cpkkd @20keV、Highly suppress radon gas level around Ge detector.
New technique on surface event at low E.Ground 0.5y +UL 2.5y
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R&D on the Key Ge technologies
• 76Ge enrichment;
• HPGe crystal growth;
• HPGe detector fabrication;
• ULB-VFE including substrate and cables;
• ULB-Copper production in underground
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CDEX-10X
Detector fabrication on two 0.5kg PCGe with <350eV;
Totally new design by CDEX and background control with pure cable, VFE substrate and structure materials;
R&D on two preamp types: JFET and ASIC;
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Detector Fabrication
Successful on 10 g/500 gEnergy resolution : 0.95% @ 59.5 keV(10 g) 0.17% @1173 keV(500 g).
500 g PCGe with home-made fabrication will be studied at CJPL soon.
0.169%@1173keV
0 100 200 300 400
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200
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Co
un
ts
Channel
241
Am
7#点电极
HV=350V,t=4us
Peak=323.99
1.48%@59.5KeV
Low Chan=10
Peak=50
~10KeV
0.95%
@59keV
PCGe Detector-19# (ø50mm)
Bias (V) 800 900 1000 1100 1200
Leakage
Current (pA)1 3 6 7 13
Bias (V) 1300 1400 1500 1600 1700
Leakage
Current (pA)19 39 97 188 922
Mass of 10 g
Front-End electronics design
PPC
HPGeASIC
VD
VO
Ct
G
T
Vacuum Chamber
Silicon
substrate
Wires
HVHV Feedthrough
Signal Feedthrough
Signal cables
HV cable
ROOM Temperature:
HV/
Preamplifier/
Fan out buffersJFET D
S
Cf
Ct
Rh
F
T
H1
H2
CuFlon
substrate
Heating
Resistor
LN Tank
~0.3m
OR
~1.5m
Readout Scheme
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• JFET based readout
Test on JFET bonded on CuFlon substrate
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10
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80 100 120 140 160 180 200 220 240 260 280 300
ENC(e)
温度(K)
ENC @ Cd=0 vs. Temperature
Preamp ASIC bonded on Test PCB
• CMOS ASIC based readout
0 5 10 155
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25
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Cin (pF)
EN
C (
e)
ENC=1.38*Cin+4.46
ENC=1.43*Cin+4.86
Temperature=77K
leakage =0.1pA
shaping time=8us
shaping time=12us
Experiment
R&D on Front-End electronics
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Best sensitive in the range
of 10GeV, ~10-44cm2
76Ge double beta decay
research(join LEGEND
Collaboration)
Projected results
A by-product result to see where we are.
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Outlook & Prospects
CDEX-1@CJPL has been commissioned from 2011.Results of light WIMPs and axion searches from CDEX-0/1 have been achieved. (PRD-2013, PRD*2-2014,PRD-2016, PRD-2017). Results of annual modulation based on background understanding are coming soon.
Three 3 kg arrays detector(with two) in LN@CJPL is intensively studied. Lower background level is going to be pursued.
R&D on the Key technologies for detector fabrication, crystal growth, upgraded electronics as well as electroformed copper.