New Experiments With Spheres
The NEWS Project
Bei Cai for the NEWS collaboration
Queen’s University
SNOLAB Users Meeting Symposium
September 1-2, 2016
Spherical gas detector working principle
Drift region
Ampl region
rs
rc
E≈V/r2*rs
for rc>> rs
Bei Cai
• Large metallic sphere grounded
• Small sensor (1-16 mm) in the center of
detector on positive high voltage
• Filled with gas mixture
• Particle interaction creates electron-ion
pairs in the gas
• Electrons drift and create avalanches
toward center of detector
• Ions drift toward the ground and induce
current/charge on the electrode
• Measured signal is proportional to
particle energy
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Spherical gas detector
Drift region
Ampl region
rs
rc
E≈V/r2*rs
for rc>> rs
Bei Cai
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Simple detector design
Low radioactivity
Very low energy threshold
Low mass targets (H, He, Ne),
sensitive to low-mass WIMPs
• Flexible gas pressure and
interchangeable sensor size
• Single signal readout channel
• Good energy resolution
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Gas mixture
• Noble gases, hydrogen and nitrogen have low
electron attachment coefficients. Electrons
continuously migrate
• Quench gas is necessary
– Avalanche is based on secondary ionization. However
gas molecule may be raised to an excited state but not
ionized. This excited state decays by photon emission.
These photons interact with gas molecule and produce
secondary electrons, which distort proportionality of
the gas detector
– Quench gas is added to absorb these photons. Often
this quench gas is methane (CH4)
Bei Cai
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NEWS-LSM detector
Located at Modane
Underground Laboratory
4800 m.w.e.
NEWS-LSM detector and shielding
Low radioactivity copper, 60 cm
diameter, 6 mm sensor
Shields 4 to 7 cm Cu, 10 cm Pb, 30 cm PE
Operation and data taking conditions
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Use of 3.1 bar Ne/CH4 mixture with 0.7% CH4
Energy to ionize a single electron in Neon w = 36 eV
High Voltage on sensor set to 2520 V, no sparks
Gain around 3000
Sealed mode, no recirculation
Data taking continuously for 42 days
12.6 kg*day exposure
Acquisition threshold set at around
50 eV, no noise in stable conditions
• Loss of gain around 4% overall
monitored with 210Po alpha line
• Calibration in energy with 37Ar gas
source (from (n,a) reaction on 40Ca)
• Anticipated main backgrounds :
– Compton (volume)
– 210Pb decay products (surface)
Comparison of simulation with AmBe
neutron calibration data
Pusle simulations include radial field and diffusion
WIMP search
data
ROI
Side bands for background
(surface & Compton)
used for preliminary
analysis
Show strong component of
surface events in data
“Conservative” analysis
1) Apply threshold cut at 150 eV
2) Simulations and side bands are used to determine volume and
surface populations
3) Given expected shapes of background contributions in ROI, use
Boosted Decision Tree analysis to determine cuts to optimize
signal/background discrimination
Expected sensitivity (SI) of the NEWS-LSM
assuming events in ROI are pure backgrounds and behave in ROI as expected
SuperCDMS
Expected sensitivity of this experiment
CRESST
2016
DAMIC
Background free limit with
present exposure
LUX
Limit set on spin independent coupling WIMPs with standard assumptions on WIMP
velocities, escape velocity and with quenching factor of Neon nuclear recoils in Neon
calculated from SRIM
Inside a sound-proof room
15 cm stainless steel sphere
(S15)
NEWS at Queen’s
Pressure transducer
Gas line
To vacuum pumps
Detector sensor design
HV2
HV1
Bei Cai
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Raw pulse
Gain/stability studies
with Fe-55 X-rays
Fe-55 6 keV X-rays
Time bin (µs)
Ne+2%CH4
500 mbar
HV1 (ball) = 650 V
HV2 (umbrella) = 72 V
Alphas in S15
Ar+2%CH4, 1 bar
HV1=1 kV, HV2=167 V
Po-210 alpha rate < 3 mHz
Po-210
2% energy [email protected]
Po-218
Po-214
Bei Cai
Integral of pulse
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Laser calibration
• Nitrogen gas laser produces UV photons
• Photons extract surface atomic electrons
from stainless steel sphere
• Electron drift time and diffusion time
measurements – to be compared with
simulations with Magboltz
• Single electron measurement
• Looking into solid state laser to
study stability of detector gain
Bei Cai
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Laser calibration
N2 laser (60 electrons)
Ne+2%CH4
200 mbar
HV1 = 550 V
HV2 = 69 V
Fe-55 6-keV X-rays
Amplitude (ADU)
Bei Cai
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Electron drift/diffusion time study
• Timing difference between laser trigger pulse and gas detector
signal  electron drift time
• Width of the distribution  electron diffusion
Peak @ 15 µs
Sigma is 1 µs
Ne+2%CH4
1 bar
HV1 = 1050 V
HV2 = 170 V
Bei Cai
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Two new prototype
detectors at Queen’s
30 cm diameter high pressure
stainless steel vessel
and 50 cm diameter stainless
steel sphere
NEWS-SNO
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140 cm diameter copper sphere
Operates up to 10 bar pressure
Ne, He, CH4 gas mixture
Clean copper: 1 uBq/kg uranium and thorium content
Compact lead & polyethylene shield
Lead shield
Copper sphere
Bei Cai
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NEWS at SNOLAB
NEWS-SNO will be located in the
Cube Hall next to the DEAP-3600
and MiniCLEAN detectors
MiniCLEAN
40 cm PE shield
DEAP-3600
NEWS-SNO
35 ton lead shield
Bei Cai
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NEWS-SNO status
• Detector and shield designs are finalized
• Prototype copper sphere has been produced in France,
samples sent to PNNL for radiopurity assay
• Sensor design and test are ongoing
• Gas handling system is being implemented and tested at
Queen’s
• Radioactive source and laser calibration system are
being finalized
• SNOLAB Gateway 2 review is scheduled for this October
• Detector installation at SNOLAB is expected to start in
fall 2017
Bei Cai
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NEWS-SNO R&D programs
Queen’s University
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Single electron response study
Gain stability
Drift time & diffusion measurements
Surface background (implanted alpha sources) study
Calibration system and source deployment testing
LSM
• Internal surface cleanliness using high pressure water jet
• Further data taking with He and H rich gas
Grenoble
• Quenching factor measurement with ion beams below 1 keV
TUM
• Gas scintillation properties & Laser studies
PNNL
• Plan for electroforming of copper vessel for future NEWS detector
Bei Cai
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Projected NEWS-SNO spin-independent WIMP sensitivity
CDMSLite1
DAMIC
CRESSTII
H
2017
COGeNT
He
CDMSLite2
CDMS_Si
DAMA
NEWS-SNO
CRESST
Ne
DarkSide50-Ar
Edelweiss LE
CDMS-Edelweiss
CDMS reanalysis
Xenon
LUX
Multi-ball ACHINOS structure
Developed in Saclay in collaboration with University of Thessaloniki
Volume electric field tuned by the structure and ball size
Multichannel signal
Detector segmentation, directionality for dark matter
Bei Cai
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Additional physics prospects
• Neutrino-nucleus coherent elastic scattering
– D. Z. Freedman, Phys. Rev. D, 9(1389) 1974
• Dedicated supernovae detector
– Simple and cost effective - lifetime >>1 century
– Could be a worldwide network of several of such dedicated
Supernova detectors. To be managed by an international
scientific consortium and operated by students
– Y. Giomataris, J. D. Vergados, Phys. Lett. B, 23(634) 2006
• Competitive double beta decay experiment with Xe-136
at 50 bar
– I. Giomataris, J. Phys. Conf. Ser., 309(2011) 012010
Bei Cai
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Summary
• NEWS-SNO is a spherical gas detector to be
located at SNOLAB, sensitive to low mass WIMPs
• Installation is expected to start in 2017
• 12.6 kg*day of neon data using a 60 cm low
radioactivity prototype (NEWS-LSM) is currently
being analyzed
• Preliminary analysis results for WIMP sensitivity
are promising and pave the way to the larger
scale detector to be installed at SNOLAB
• Gas characterization and calibrations are ongoing
with small prototype detectors at Queen’s
University
Bei Cai
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Collaboration meeting at Modane, France in April 2016
NEWS Collaboration
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Queen’s University Kingston – GG, P di Stefano, R Martin, T Noble, B Cai,
A Brossard, A Akamaha, P Vasquez dS, Q Arnaud, K Dering, J McDonald, M Clark, and summer students
Copper vessel and gas set-up specifications, calibration, project management
Gas characterization, laser calibration, on smaller scale prototype
Simulations/Data analysis
IRFU (Institut de Recherches sur les Lois fondamentales de l’Univers)/CEA Saclay -I Giomataris, M Gros, C Nones, I
Katsioulas, T Papaevangelou, A Gigagnon, JP Bard, JP Mols, XF Navick,
– Sensor/rod (low activity, optimization with 2 electrodes)
– Electronics (low noise preamps, digitization, stream mode)
– DAQ/soft
LSM (Laboratoire Souterrain de Modane), IN2P3, U of Chambéry - F Piquemal, M Zampaolo, A DastgheibiFard
– Low activity archeological lead
– Coordination for lead/PE shielding and copper sphere
Thessaloniki University – I Savvidis, A Leisos, S Tzamarias, C Elefteriadis, L Anastasios
– Simulations, neutron calibration
– Studies on sensor
LPSC (Laboratoire de Physique Subatomique et Cosmologie) Grenoble - D Santos, JF Muraz, O Guillaudin
– Quenching factor measurements at low energy with ion beams
Technical University Munich – A Ulrich
– Gas properties, ionization and scintillation process in gaz
Pacific National Northwest Lab– E Hoppe
– Low activity measurements, Copper electroforming
Associated lab : TRIUMF - F Retiere
June 2016
– Future R&D on light detection, sensor
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