Performance of the SoLid Reactor Neutrino Detector - PPNS 2018 - - - PowerPoint PPT Presentation

Performance of the SoLid Reactor Neutrino Detector

• PPNS 2018 -

Maja Verstraeten

• n behalf of the SoLid collaboration

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Overview

The sterile neutrino The SoLid neutrino detector @ the BR2 reactor Construction and QA Commisioning and callibration

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Overview

The sterile neutrino The SoLid neutrino detector @ the BR2 reactor Construction and QA Commisioning and callibration

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The sterile neutrino hypothesis

Reactor -and Gallium anomalies can be explained by an additional mass state Small correction to 3x3 neutrino mixing can explain unexpected active neutrino

• scillation data

Sterile neutrino not detectable through weak interaction. Only indirect measurement possible

/ measured predicted rate

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Sensitivity to a new neutral state

Oscillation dictated by properties of sterile neutrino Best fit gives Δm² ~ 1.73 eV² and sin²(2θ) ~ 0.1

Oscillation apparent over distance and energy Coverage in L/E requires a good position -and energy resolution

Indication of research space

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Reactor spectrum distortions

Energy spectrum distortions seen by all three reactor experiments with high significance (dubbed “the bump”) Amplitude of effect correlated with reactor power

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Overview

The sterile neutrino The SoLid neutrino detector @ the BR2 reactor Construction and QA Commissioning and callibration

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Challenges at VSBL

Detector

Oscillation search demands high spatial -and energy resolution Effective background rejection required, while facing low

• verburden and reactor radiation

Reactor

VSBL search demands compact reactor core with well understood fuel composition Reactor site poses safety -and security implications

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Challenges at VSBL SoLid solutions

SoLid detector

High segmentation gives 3D spatial information Suitable photo detectors give energy resolution Active and passive shielding

BR2 Research reactor

Belgian Reactor 2 (BR2) at SCK-CEN Twisted design of fuel matrix gives compact core High enriched uranium fuel Access ports for experiments, on axis with reactor core

Detector

Oscillation search demands high spatial -and energy resolution Effective background rejection required, while facing low

• verburden and reactor radiation

Reactor

VSBL search demands compact reactor core with well understood fuel composition Reactor site poses safety -and security implications

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BR2 nuclear site

Compact research reactor

⌀50 cm and heigth 90 cm Fuel 93.5% 235U Thermal power 50-80 MW Duty cycle 150 days/year (~1month cycles) SoLid at baseline 6-9 m

Low background site

Low neutron and gamma fluxes No surrounding experiments Overburden 10 m.w.e.

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SoLid Phase 1 detector

5cm cubes give resolution on 3D topological information 16x16 cubes stacked in planes Planes grouped per 10 in 5 modules, Modules installed on movable rail system 1.6t fiducial mass

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SoLid Phase 1 detector

Target sensitivity

Energy resolution IBD efficiency 30% Signal to background 3:1

Container 2.4x2.6x3.8 m³

Cooled to 10°C to reduce MPPC dark count rate (~1/10)

Shielding

Water walls: 50cm thick, 3.4m high, 28t Polyethylene ceiling: 50cm thick, 6t Cadmium sheets

→Full Geant4 simulation

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SoLid detection principle

Anti-electron-neutrinos detected through inverse beta decay (IBD) in the composite scintillator element Prompt positron signal

Positron energy contained in PVT cube Allows localisation of interaction Gives the anti-neutrino’s energy

Delayed neutron signal

Neutron captured in 6LiF:ZnS close to interaction

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SoLid signal

Example of prompt and delayed coincidence

First reactor cycle in december 2017 First prompt delayed candidates

Δt = 40µs

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Trigger sheme

Data-rate of digitised MPPCs of ~3 Tb/s total T riggers and sophisticated online data reduction to handle data rate

Counting peaks over threshold in local timewindow Dedicated PSD algorithm developed for neutron signals: ~80% effjcient.

Large bufger around neutron delayed signal (700µs and 7 planes) to collect prompt signal

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SoLid signal identification

Positron (EM) and neutron signals discriminated based on pulse shape (peaks over threshold) IBD signal identified by

Δt = tdelayed – tprompt Δr = |rdelayed – rprompt| Prompt energy Others include multiplicity, directionality and fiducial layer

Simple cut based analysis shows significat reduction in backgrounds

Prototype results

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Overview

The sterile neutrino The SoLid neutrino detector @ the BR2 reactor Construction and QA Commisioning and callibration

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Plane construction

~13 000 cubes manually washed, weighted, wrapped, stacked,... All cube components product information stored in database

PVT mass Li mass Total mass Fiducial mass

Frame

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Plane qualification

‘Calipso’ automated robot for X Y scanning of planes with calibration sources Practice run with SoLid electronics and software

Each cube scanned with at least two sources:

Gamma source to test cube & channel light yield. Neutron source to test cube neutron effjciency.

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Plane qualification – gamma source

Measuring the compton edge of 1270 keV gammas from 22Na demonstrates Light yield > 60PA/MeV. LY~30% higher than expectations. Homogeneous response

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Plane qualification – neutron source

Neutron source demonstrates high and homogeneous neutron reconstruction effjciency (trigger + ID) Comparison with MC indicate reconstruction effjciency > 60% (GEANT4 simulation) Identifjcation and correction of issues before plane installation in module

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Plane qualification

Difgerent source show high linearity

combined with 235U this gives a strong handle on 5 MeV distortion

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Overview

The sterile neutrino hypothesis The SoLid neutrino detector @ the BR2 reactor Construction and QA Commisioning and callibration

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Commissioning at BR2 reactor

Commissioning of the full detector completed begin of February 2018 Expected ~150 reactor on data in 2018

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MPPC equalisation

99% channels operational Amplitude response calibrated to high quality, spread ~1% Voltage scans used to calibrate individual MPPC breakdown voltages and amplifjcation responses Equalise for gain response (i.e 1 PA amplitude) of 32.0 ADC/PA - equivalent to 1.8 V over-voltage SoLid preliminary

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Calibration at BR2 reactor

Second calibration robot in situ: CROSS Sits above detector planes. Mechanically open gap between sets of ten planes Source free to move in gap

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Calibration at BR2 reactor – gamma

Per plane ~Homogeneous response Row with low LY identifjes coupling from fjber to MPPC

• r mirror with problems

Global data Preliminary results in 96% of cubes (Average of plane is used for non calibrated cubes) Clear attenuation pattern - will be corrected

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Calibration at BR2 reactor – neutron

Clear neutron identifjcation after neutron trigger Absolute neutron reconstruction effjciency over all detector cells (T rigger + ID) Neutron reconstruction effjciency during commissioning > 75%. Statistical error per cube wih mean value of 2.5% and max of 6%

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Calibration at BR2 reactor

Excellent agreement between calibration at 1.27 MeV and 4.4 MeV Good indication of linearity in energy response Need to validate with more sources

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Calibration with muons

SoLid prototype

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Physics data taking

Stable data taking since february Highly stable for both reactor on and ofg

Online, live, remote detector monitoring Online event reconstructjon for subsample of data Physics variables available

• nline

Recons ZnS rate

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Conclusion

Constructjon and installatjon of SoLid detector completed in December 2017 Commissioning of SoLid detector at BR2 research reactor fjnished early 2018 Channel response amplitude calibrated to ~1% First calibratjon results indicate a good uniformity and linearity

• f the signal

Trigger effjciency and light yield are higher than expected Physics data taking and fjrst analysis ongoing

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Thank you for your attention