Download 1 kg -1 - Daya Bay Reactor Neutrino Experiment in Hong Kong

Ultra-Low Energy Germanium Detectors for
Neutrino-Nucleus Coherent Scattering
and Dark Matter Searches
 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
Henry T. Wong /王子敬
Academia Sinica /中央研究院
@
OCPA Workshop
July 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
Kuo Sheng Reactor Neutrino Laboratory
Front Gate
28 m from core#1 @ 2.9 GW
Shallow depth : ~30 meter-water-equivalent
Reactor Cycle : ~50 days OFF every 18 months
Front View (cosmic vetos,
shieldings, control room …..)
Configuration: Modest
yet Unique
Flexible Design: Allows
Inner Target Volume
different detectors conf. for
different physics
Reactor Neutrino Interaction Cross-Sections
quality
Detector requirements
mass
1 counts /
kg-keV-day
On-Going
Data Taking
& Analysis
R&D :
Coh. (nN)
T < 1 keV
Results :
SM s(ne)
mn(ne)
T > 2 MeV
T ~ 1-100 keV
Reactor Neutrino Spectra Evaluation…
Reactor Operation Data
ne
Nuclear Physics
Neutrino Electromagnetic Properties : Magnetic Moments
requires mn0
e.g.
 a conceptually rich subject ; much neutrino physics &
astrophysics can be explored
n-osc. : Dmn , Uij
0nbb : mn , Uij , nD/nM
mn
: mn , Uij , nD/nM , n  g
 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
Direct Experiments at Reactors
ds (ne)   2  1  1  m 2
m
dT
me2 T En  n
KS Limit:
mn(ne) < 7.4 X 10-11 mB
@ 90% CL
Search of mn at low energy
 high signal rate & robustness:
 mn>>SM [ decouple irreducible bkg  unknown sources ]
 T << En  ds/dT depends on total fn flux but NOT
spectral shape [ flux well known : ~6 fission-n  ~1.2
238U capture-n per fission ]
 GEMMA-07 (Ge+NaI): mn(ne) < 5.8 X 10-11 mB
“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 threhold1 kg mass1 cpd detector]
 physics :
 nN coherent scattering
 Low-mass WIMP searches
 Improve sensitivities on mn
 Implications on reactor operation monitoring
 Open new detector window & detection
channel available for surprises
Neutrino-Nucleus Coherent Scattering :
Standard Model
Cross-Sections:
 a fundamental neutrino interaction never been experimentallyobserved
 s~N2 applicable at En<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
Expected Interaction Rates at KS @
different Quenching Factors
e.g. at
c.f.
QF=0.25 & 100 eV threshold
Rate ~ 11 kg-1 day-1 @ KS
nN (Ge;1 keV) @ accelerator ~ 0.1 kg-1 day-1 ;
(water) @ KS ~ 1 kg-1 day-1
nne-p
e
 by-product : T>500 eV gives
mn(ne)  ~ 10-11 mB at ~ 1 cpd background
Sensitivity Plot for CDMWIMP direct search
Low (<10 GeV) WIMP Mass / Sub-keV Recoil Energy :
 Not favored by the most-explored specific models on galacticbound 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
43mm
4 X 5 g
DETECTOR VIEW INSIDE ENDCAP
AND INPUT STAGE LOCATIONS
Input stage
location of the
preamplifier
Signal side
S1
B
20mm
S2
A
S1
43mm
S2
10
mm
S3
S4
ENDCAP
Diameter :
<85mm
Crystal
Holder
AB view
Crystal
Copper
shielding to
be defined
Segmented 180 g
with dual readout
20mm
S4
A
S3
B
High Voltage
side
Cooling finger
R&D Program towards Realistic O(1 kg) Size
Experiments (both nN & CDM) :
 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
Yang-Yang Underground Laboratory
 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
Y2L
Single Readout Event ID – correlate channels with different gains & shaping times
e.g.
4 X 5 g
Sampling of Specific
Range for non-triggerChannel 2 – i.e. look for
+ve fluctuations at
specific and known times
Energy as defined by trigger-Channel 1
Noise
Ch #1 :
Ch #2 :
Signal
Dual Readout Event ID – correlate anode/cathodes in amplitude & timing
Peak Position+Amplitue Correlations in Electrodes
Calibration spectrum (55Fe) Raw/PSDs
Threshold
~ 250 eV
Seg. 180 g
Noise
Cathode :
Anode :
Signal
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
Sub-keV Background Measurements & Comparisons
4 X 5 g
(~1 yr apart)
1 kg
5 g
 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
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
g-induced bkg is flat while ninduced 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
Improved PSD ;
dual-readout
coincidence
Scale up to compact 1 kg ;
understand background
source (g/n) ; improved
shielding design
AS better
electronics
noise levels
Quenching Factor Measurement for Ge at
CIAE’s Neutron Facilities:
With 13 MV Tandem
Goals for 2008 Runs :
 Use actual ULEGe 100-eV detector
 Use lower energy neutron beam
(860 keV50 keV) with a pulsed-LE
tandem
Detector Scale-up
Plans:
p
S1
S0
 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.
Another Possible Design for O(1 kg) Segmented ULEGe :
※3X3X5 elements @ 20 g each (i.e. 900 g)
※Dual readout per element
※veto ring  lids
2D Projection
Summary & Outlook
An O[100 eV threshold1 kg mass1 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