Starting Points (Collaboration ; Laboratory ) 1-kg HPGe : Magnetic Moment Results
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Transcript of Starting Points (Collaboration ; Laboratory ) 1-kg HPGe : Magnetic Moment Results
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