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Energy calibration of the SoLid detector.


Academic year: 2021

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Submitted on 29 Jan 2020

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Energy calibration of the SoLid detector.

David Henaff

To cite this version:

David Henaff. Energy calibration of the SoLid detector.. 16th International Conference on Topics in Astroparticle and Underground Physics, Sep 2019, Toyama, Japan. �hal-02458983�


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Energy calibration of the SoLid detector

David HENAFF on behalf of the SoLid Collaboration

SUBATECH, CNRS/IN2P3, Universit´e de Nantes, IMT Atlantique, Nantes, France


Energy calibration of the SoLid detector

David HENAFF on behalf of the SoLid Collaboration

SUBATECH, CNRS/IN2P3, Universit´e de Nantes, IMT Atlantique, Nantes, France


Physics motivations: Two outstanding issues in neutrino physics:


Recent short baseline neutrino

ex-periments revealed anomalies:

– Gallium Anomaly (GA): ∼ 10% deficit in the measured neutrino flux from sources calibrat-ing solar radiochemical experiments. [1]

– Reactor Antineutrino Anomaly (RAA): ∼ 6% (3 sigmas) deficit in measured antineutrino flux wrt updated predictions. [2]

Could indicate the presence of new neutrino state: sterile neutrino !

2. Distortion (”5 MeV bump”):

• Observed in the antineutrino energy spectrum by ex-periments that measured θ13. [3]

• Reactor prediction or experimental problem?

The SoLid experiment

In a nutshell:

Measurement of reactor νe flux and spectrum. • At very short baseline: Sensitive to sterile oscillation.

• BR2 research reactor at SCK·CEN: Highly enrichment in

235U constraints flux and spectrum predictions.

• Novel technology: PVT + ZnS scintillators: Different energy response than for liquid scintillators: More precise energy reconstruction.


• Close to a reactor and on surface: Huge reactor and cosmic backgrounds (n,γ,µ).

• Oscillation to be resolved in a few meters: Highly seg-mented detector.

The SoLid detector:

• Detection principle: Inverse Beta Decay (IBD): νe + p −→ e+ + n

• 3D reconstruction of interactions:

– 50 planes of (16 × 16) 5 × 5 × 5 cm3 cubes.

– Cube wrapped with 6LiF:ZnS sheets for neutron capture:

n +6 Li →3 H + α

– Scintillation photons captured by network of wavelength shift-ing fibres and read-out by 3200 SiPMs.

– PSD discrimination between Electromagnetic Signal (ES) and

Neutron Signal (NS).

Challenging calibrations

Unprecedented calibration:

• Sterile and distortion analyses require to have a 2% precision for the energy scale.

• 12800 cubes read-out by 3200 channels have to be calibrated individually to cor-rect inhomogeneity.

• 2 types of calibration performed γ and n: Measure the response of PVT and ZnS scintillators.

• Calibration based on Compton Edge (CE), no photo-peak due to size of cubes. • Need fast calibration to maximize physics data taking: High activity sources and specific DAQ configuration.

Typical calibration configuration:

• Dedicated in-situ robot for calibration purposes called CROSS.

– Allows us to place the source between modules. 9 positions per gap and 6 gaps. Neutron calibration:

Source AmBe 252Cf Activity [n/s] 1794 ± 35 3763 ± 44 Emean [MeV] 4.2 2.1

– Neutron activity measured by the National Physical Laboratory (UK) to reduce uncertainty on neutron re-construction efficiency.

– Full scan of the detector with one source in 3 days.

Gamma calibration:

Source: 22Na 137Cs 60Co 22Na 207Bi AmBe True energy of CE [MeV]: 0.341 0.477 1.04 1.054 0.858 + 1.547 4.2 – 22Na principal source, full scan in 1 day.

– Read-out only ± 5 planes around the source to avoid dead time.

– Threshold or random trigger depending on the energy of the source.

– Two different methods to control systematic uncertainties, agreement at 2%.

Light yield and resolution measurement

Light collection:

Deposited energy in PVT cube (MeV) Number of scintillation photons produced Number of scintilla-tion photon in fibre 1 Number of

scintilla-tion photon in fibre 4

Reach sensor 1 reach sensor 4

Detected in sensor 1 (PA) Detected in sensor 4 (PA)

Scintillation efficiency Light collection efficiency Fibre’s attenuation Sensor efficiency

. . .

. . .

. . .

Energy calibration:

SiPM calibration:

• 2nd generation Hamamatsu Sil-icon Photo-Multiplier

• Gain and cross-talk measured for each sensors

• SiPMs equalised for uniform single pixel avalanche amplitude response

Using calibration sources:

• Two methods have been developed to extract the Compton Edge value [JINST14 P02014]

Kolmogorov approach:

• Simulate a calibration run with Geant4

• Smear the true deposited energy for several LY and resolution val-ues

• Take parameters for which a Kolmogorov-Test is maximal

Analytical approach:

• Use the Klein-Nishina formula as true deposited energy p.d.f.

• Perform the convolution with an energy dependent gaussian to take into account of detector re-sponse

• Extract with a fit the CE and the resolution

Using muons:

• Muons crossing the detector dur-ing physics data-takdur-ing are used to monitor the energy scale


• Construct dE/dx distribution per channel

• Fit Landau gauss to each channel • Make MPV distribution to extract



• Achieve to calibrate 12.800 cubes in 1 day using Na22 source

• Control of the energy scale in the IBD energy range

• Linear detector response ob-served


• Full detector calibrated:

7→ Light Yield has been determined in all cube, 77PA/MeV with a resolution of 12% at 1 MeV. 7→ Linearity response of PVT has been proven

be-tween 1 and 8 MeV.

• Ongoing work:

7→ Calibration below 1 MeV is ongoing.

7→ Regular calibration campaign scheduled.


[1] Carlo Giunti and Marco Laveder. “Statistical significance of the gallium anomaly”. In: Phys. Rev. C 83 (6 2011), p. 065504.

[2] G. Mention et al. “Reactor antineutrino anomaly”. In: Phys. Rev. D 83 (7 2011), p. 073006.

[3] Y. Abe et al. “Improved measurements of the neutrino mixing angle θ13 with the Double Chooz


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