scintillating bubble chamber for wimp dark matter and
TRANSCRIPT
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Scintillating Bubble Chamber for WIMP Dark Matter and CEνNS Detection
Jianjie Zhang
Northwestern University
8/7/2017
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Outline
• Motivation: GeV WIMPs and reactor neutrinos
• The scintillating bubble chamber technique
• Results from a 30-gram xenon prototype• arXiv:1702.08861 [PRL 118, 231301]
• Current status and next steps: lowering thresholds, liquid Argon target
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What could you do with a liquid-noble bubble chamber?
• Discriminating• Only sensitive to nuclear recoils (neutrons, neutrinos, and
WIMPs), ~1010 ER discrimination• Scintillation channel eliminates bubble-nucleating
backgrounds at other energies (e.g. alpha decays, surface wetting phenomena)
• Scalable• Largest bubble chamber to date: 35 m3 (BEBC)• Ton-scale low-background bubble chamber in works (PICO)
• Low threshold• Sub-keV recoil energy threshold is moving from “plausible” to
“realistic”
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1 ton-year at 1-keVr threshold(76 8B neutrino events expected)
What could you do with an argon bubble chamber?
arXiv:1707.04591
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What could you do with an argon bubble chamber?
Up to an event-per-minute in a m3 target,only background is neutrons
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Bubble Chamber Thermodynamics
• What does it take to nucleate a bubble?
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Pl=25 psia, Tl=–45oC
Pb= 187psia
Xerc=13.3nm
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Bubble Chamber Thermodynamics
• What does it take to nucleate a bubble?
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Pl=25 psia, Tl=–45oC
Pb= 187psia
Xerc=13.3nm
0.61 keV
-0.07 keV
0.55 keV
Surface energy, Bulk energy, Reversible Work
= 1.09 keV total
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Bubble Chamber Discrimination
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Electron recoil sensitivity in C3F8 and CF3I from various PICO calibration and dark-matter chambers
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Nuclear Recoil Sensitivity
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Neutron Calibrations in C3F8 @ ET = 3.2 keV
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NU Xenon Bubble Chamber
-65 to -43 °Csuperheated
-105 °Cnormal
Mirrors
To hydraulic controller
PMT
Camera
LXeIR
illum
inatio
n
Vacuum cryostat
PiezoScintillation &Bubble
Muon paddle
Sapphire window
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Assembling*the*detector*
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NU Xenon Bubble Chamber
• First Bubbles June 2016
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June 2015
Sept 2015
Feb 2016
April 2016
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Sample Nuclear Recoil Event
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z
z
Dt
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Acoustic – Scintillation Coincidence
• < 1% accidental coincidence rate in calibration data
• Slope = speed of sound in xenon (to 20%)
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Xe
Gamma Rejection
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Xe
Preliminary [PRL 118, 231301]
Gamma rejection background limited.90% Poisson upper limit set without background subtraction
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Scintillation Spectrum for Bubble Events
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ET = 8.2 – 8.6 keVET = 8.6 – 15 keV
*Simulation assumes15-keV threshold for bubble nucleation
Based on rate alone, NR threshold is 19 ± 6 keV
Bubbles with no PMT Trigger
No ET dependence observed inother bins
*
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Current Status and Next Steps
• Simultaneous bubble nucleation and scintillation for nuclear recoils demonstrated
• Bubble nucleation by gammas <10-6 at ET=1.0 keV
• Nuclear threshold analysis ongoing at ET=1.0 keV• Now calibrating sensitivity to low-energy nuclear recoils
using (γ,n) sources
• Reconfiguring the xenon chamber to use liquid Aras target fluid
• Ready to scale up soon
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