Water-based Liquid Scintillator (WbLS) Technology

Minfang YehNeutrino and Nuclear Chemistry

NNN2016, IHEP, Beijing, Nov. 2016

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Cerenkov (e.g. Super-K, SNO)

water-like WbLS• Cerenkov./Scint.

detection

Oil-like WbLS• Metal-loaded LS

Water-based Liquid Scintillator

Scintillator (e.g. SNO+, Daya Bay)

LS WbLS H2O

If you always do what you always did, you will always get what you always got. -Albert Einstein

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KamLAND

Daya Bay

SNO+

NoVA Borexino

An excellent detection medium for neutrinos in MeV range

Neutrino Interactions in Scintillator

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KamLAND

Daya Bay

SNO+

NoVA Borexino

An excellent detection medium for neutrinos in MeV range

Neutrino Interactions in Scintillator

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Scintillator ApplicationsProton decay 0νββ Solar neutrinos (w 7Li loading)Geo-neutrinosSupernova neutrinosDiffuse SN background neutrinos long baseline neutrino physics (w accelerator neutrino source)Sterile neutrinos (w neutrino source)Ion-beam therapy imagingTOF-PETSome details in arXiv:1409.5864

zsolvent WLS

fast and slow components

Scintillation Mechanism

WbLS follows the same scintillation transition mechanism with quenching from water

wiki

Stokes shift

fast

slow

Ranucci et al.

Birk’s Mechanism

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Water-based Liquid Scintillator

A novel scintillation liquid ranging from pure organic to pure water• Cherenkov (directional) and scintillation (isotropic)

- Energy measurement below Cherenkov threshold (p→K+ ̅)

• Particle identification- Timing separation of fast Cherenkov

from slow scintillation• Adjustable scintillation light yield (0%~15% LS)• Long attenuation length • Cost effective (~$30/ton) compared to LS ($3k/ton)• Environmental for confined space or close to

accelerator facility) A new metal loading technology to

hydrophobic elements: Te, Li, K, Pb,…,etc.

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LSND rejects neutrons by a factor of 100 at ¼ Cherenkov & ¾ Scintillation light (NIM A388, 149, 1997).

20%LS give ~50% light as a pure LS

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K+ μ+ e+

μ+

e+

Hit Time (Time of Flight Corrected) [ns]

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f PE

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p → K+ + ν e+ + νμ + νe _μ+ + νμ

12 ns 2.2 μs

WbLS Physics below Cherenkov

• A simulated event with 90 photons/MeV in a SK detector for (p→K+ ̅ ) mode• An order of magnitude improvement over the current SK sensitivity

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Metal-doped Liquid Scintillator

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Ex. 0.1% 6Li-doped LS

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Optical stability from 05/2015 to 09/2016

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Ex. 0.1% 6Li-doped LS)

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Light-yield (~8000 photons/MeV) stability from 05/2015 to 09/2016

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Ex. 0.1% K-doped LS

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0.1%K-WbLS 071420160.1%K-WbLS 08162016

• scintillator non-linearity (low-energy) • Key aspect for JUNO?

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Ex. 8.24% Pb-doped LS

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8.24%_Pb

• Solar neutrino target• Total gamma spectrometry

• Medical imaging, QA/QC phantom (2 patents)• Nonproliferation (SBIR)

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Ex. 8.24% Pb-doped LS

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~5000 photons/MeV

F. Reines

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Ex. 0.1 wt% Gd-LS

DayaBay

Accelerator n n

• 0.1% wt% Gd-doped LS (demonstrated by Daya Bay)• Radiopure (LZ) • PSD-improved and Cherenkov separation for detector operated on surface close to

reactor/beam facility (JSNS2 or other accelerator physics experiment)

JSNS2

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T2K ND-280NP-supportedHEP-project

WbLS Near Plan

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WATCHMAN-II (NA22)

Kick-off meeting, LBNL in 2015

two THEIA workshops (FroST) at FNAL and JGU Mainz in 2016

Multi-physics Program• Long-baseline physics (mass

hierarchy, CP violation)

• Neutrinoless double beta decay

• Solar neutrinos (solar metallicity, luminosity)

• Supernova burst neutrinos & DSNB

• Geo-neutrinos

• Nucleon decay

• Source-based sterile searches

THEIA Proto-Collaboration

THEIA

60m

A large Water Cherenkov Detector (THEIA)

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Simulated 2000 MeV proton beam in water

WbLS Proton-beam Measurements

WbLS Detectors Simulated 2000 MeV proton beam in 1%WbLS

NSRL at BNL

Ep = 210, 475, 2000 MeV

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L.J. Bignell et al 2015 JINST 10 P12009

NSRL

1% WbLS Property

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See scintillation light below Cherenkov thres. for 0.4% and 1% WbLS

LS light yield and kB consistent with other measurements in literature for LS and plastic scintillator (0.09<kB<0.19 mm/MeV)

Light yield of 1% WbLS is ~1% of LS (expect more in pure scintillator) kB of WbLS significantly larger than LS.

• Due to presence of surfactant and/or water?

Material Light yield (photons/MeV) kB (mm/MeV)

0.4%WbLS 19.9±2.3 0.70±0.14

1%WbLS 109±11 0.44±0.05

LS 9156±917 0.07±0.01

WbLS Light-Yield and Quenching

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L.J. Bignell et al 2015 JINST 10 P12009

WbLS Challenges and Development

The optical property is dominated by Rayleigh scattering (absorption length is >60m)• A (ionic/non-ionic) mixing system? • Further reduce the organic, but maintain the L.Y. by reducing quenching

WbLS is stable >1.5 ys; but material leaching could still affect the optical property• Online circulation to separate and purify the organic and aqueous phases

respectively (Nano-filtration) Demonstration of Cherenkov & scintillation separation

• CHESS at UC Berkeley• Tsinghua demonstrator• BNL 1-ton demonstrator

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0.22 um PVDF filtered omega water

Batch 9 original 030916

Batch 9 in PTFE bag (impure) 080916

0.22 um PVDF filtered Batch 9 080916

• 1% WbLS in a PTFE lined drum • PTFE is not pure (leaching)

• Optical reinstated after circulation via 0.22-µm PVDF filter

• PTFE is hydrophobic

Online Circulation with Filtration

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Contaminants such as iron ions degrade optical transparency of water detectors so they need to be constantly purified.  

How to do this for WbLS where the organic compounds need to stay in solution? 

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One could try and  separate the organic and water stream, purify the water stream, then remix.

THEIA recirculation conceptB. Svobada

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• Identification of appropriate Molecular Weight CutOff (MWCO) hydrophilic materials

• Concentration saturation effects• Surface charge effects (polar molecules can be attached to filters and create an electric field that opposes flow)

• Surface fouling• Remixing in such a way as to retain light yield

B. Svobada

...but there are many considerations

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Sterlitech CF042Nanofiltration Unit Modified atUC Davis for a permeateloop to overcome CPand for handling viscousLS compared to water

Recent success in separating outthe active WbLS components at alevel >99% with flow rates highenough to be used in THEIA

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CHESS:CHErenkov-Scintillation SeparationCHESS:CHErenkov-Scintillation Separation

12 1-inch H11934 PMTs (300ps FWHM, 42% QE)CAEN V1742 (5GHz)

675 samples (135ns window)CAEN V1730 (500MHz)

Orebi Gann research groupSupported by LBNL LDRD (FY ’15-16

Select vertical cosmic muon eventsImage Cherenkov ring in Q and T on fast-PMT arrayDetector resolution: 338±12 psAllows charge- and time-based separation

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LABTime-based

LABCharge-based

LAB/PPOTime-based

LAB/PPOCharge-based

Cherenkov detection efficiency

83 ± 3 % 96 ± 2 % 70 ± 3 % 63 ± 8 %

Scintillation contamination 11 ± 1 % 6 ± 3 % 36 ± 5 % 38 ± 4 %

CHESS:CHErenkov-Scintillation SeparationCHESS:CHErenkov-Scintillation Separation

Orebi Gann research groupSupported by LBNL LDRD (FY ’15-16

Full simulation includes detailed geometry, DAQ effects (TTS, pulse shapes, electronics noise…)

See dedicated talks at DNP, FROST (Oct ’16)arXiv:1610.02011, arXiv: 1610.XXXXXSubmitted to PRC, PRL

Charge-based separation in pure LAB

Time-based separation in LAB/PPO

Rise time = 0.75 ± 0.25 ns

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Simulated cosmic muon in water. Red points are absorbed & reflected photons

No black barrier

With black barrier

1000 liter WbLS Demonstrator Cherenkov separation as a function of %WbLS Installations of Teflon-barrier, water system,

degas, LN2 system, PMTs/electronics, DAQ Filled with water; followed by WbLS in 01/2017

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Summary

Scintillator maintains as a main-stream detection medium for neutrino detections• (Daya Bay), JUNO, LZ, JSNS2, etc.

Water-based liquid scintillator is • an ideal liquid for p→K+ ̅ by scintillation and Cherenkov detections

- Physics below Cherenkov• A cost-effect and physics-rich option to future large water Cherenkov detector (THEIA)

- HK? 2nd detector for DUNE?- Upgrades to any Gd-water detector (SK or WATCHMAN)

• A new step for metal-loaded nuclear and particle physics experiment

- 0 (SNO+), short-baseline neutrinos (PROSPECT), accelerator neutrinos, nonproliferation, medical imaging

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