STEREO

D. Lhuillier, CEA - Saclay

D. Lhuillier - AAP 2015 - Arlington VA

1

07/12/2015

ILL Site

D. Lhuillier - AAP 2015 - Arlington VA

2

07/12/2015

ILL site, Grenoble - France:

• 57 MW, compact core < 1m
• [8.9–11.1] m from core, possible extension to 12.3 m.
• High level of reactor background
• 15 mwe overburden

Goal: look for relative spectrum distortions in identical cells

6 target cells

Strategy of the Stereo Measurement

D. Lhuillier - AAP 2015 - Arlington VA

3

07/12/2015

• Oscillation pattern based on relative shape in identical cells
• Take advantage of Gd-doped liquid scintillator technology to measure accurate spectra shape.

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• Cosmic rays induced background is the final limitation:
• Overburden from water channel
• Online rejection using PSD (stat)
• Subtraction of residual background using reactor OFF periods (syst)

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• Massive shielding against reactor induce accidentals (stat uncertainty)

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• Sensitive test of the sterile neutrino hypothesis
• New reference measurement of pure ²³⁵U neutrino spectrum.

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Detector Design

D. Lhuillier - AAP 2015 - Arlington VA

4

07/12/2015

Reflective plates to suppress dependence on vertex position

Double wall vessel

Central cells in acrylic, filled with Gd-doped LS (90 x 90 x 37.5 cm)

PMTs coupled to LS via a thick acrylic buffer for a better homogeneity

Outer crown (no Gd) to improve energy reconstruction and detection efficiency

Detector Design

D. Lhuillier - AAP 2015 - Arlington VA

5

07/12/2015

• Detector vessel is built. Working on top lid machining and inner coating
• The acrylic buffers will be delivered this week
• Delivery of all remaining components expected on late February 2016
• Assembly at CNRS-LPSC in Grenoble before transportation to ILL in April 2016.

Detector vessel

Acrylic buffers

Liquid Scintillator

D. Lhuillier - AAP 2015 - Arlington VA

6

07/12/2015

• LAB 75% → protons target
• PXE 20% + DIN 5% → light yield and PSD
• Gd-complex 0.2% + 1 %THF → neutron capture
• PPO + Bis-MSB → wavelength shifters

λ ≳ 5 m

Stable

Transparent

proton recoilsc

electron recoils

PSD

PMTs

D. Lhuillier - AAP 2015 - Arlington VA

7

07/12/2015

• 8” PMT: New Hamamatsu R5912-100 with improved Quantum Efficiency, 30% at 420 nm
• Tests are handled by MPIK Heidelberg in their Faraday lab
• New PMTs basis with decoupling system delivered by LPSC-Grenoble

• All components tested and to be delivered this month.

Detector Response

D. Lhuillier - AAP 2015 - Arlington VA

8

07/12/2015

• 400 pe/MeV expected
• Resolution 11.5% (RMS for 2 MeV positrons)
• Neutron efficiency 60% with a delayed signal above 5 MeV

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• Outer crown:
• Reduces the difference on neutrons efficiency between center and border cells to 4%
• Keep the response to prompt signals identical in central and border cells

Detector Response

D. Lhuillier - AAP 2015 - Arlington VA

9

07/12/2015

• Linearity of the PMTs and electronics validated in the physics range of interest.

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• The quenching of low energy recoiling electrons introduces a dependence on the way the total energy of an event is deposited.

• Circulation of radioactive sources inside and around the detector.

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• Monitoring of the detector response by a set a LEDs.

Calibration

D. Lhuillier - AAP 2015 - Arlington VA

10

07/12/2015

3 light injection points per detector cell

+ 12 in the outer crown

Circulation of radioactive sources in calibration tubes

Calibration

D. Lhuillier - AAP 2015 - Arlington VA

11

07/12/2015

• Extra information from the deployment of sources underneath and around the detector vessel. Outer crown can be used to veto Compton events
• Possibility to tag the direction of a 511 keV γ-ray using a 22Na source coupled with a small LYSO crystal
• Setup under test with a mockup of the detector vessel.

Prototype Cell

D. Lhuillier - AAP 2015 - Arlington VA

12

07/12/2015

• The response of a prototype cell has been tested this year.
• Same height and width than final config, ½ length.
• Equipped with acrylic buffer and reflective plates
• Light signals induced in the whole volume by:
• Source outside the vessel
• Movable light diffuser
• Source in central calibration tube

Prototype Cell

D. Lhuillier - AAP 2015 - Arlington VA

13

07/12/2015

Heigth (cm)

Detected charge (a.u.)

⁶⁰Co in central tube

Top

Center

• Small vertex dependence (~5%):
• Validates the reflective plates
• Negligible impact on energy resolution
• Good agreement with the simulation

Electronics

D. Lhuillier - AAP 2015 - Arlington VA

14

07/12/2015

• Dedicated electronics hosted in TCA crate
• Front-end boards are already tested and validated
• 8-channel FADC 14 bits 250 MHz sampling
• Qtot, Qtail, tCFD and pulse
• Gain x1 and x20 for single PE
• First level programmable trigger (FPGA) validated with muon veto
• Trigger board: second level programmable trigger (FPGA) taking into account the 3 detectors : Target cells, outer crown, veto
• LED driver for light calibration

• All cards already delivered and tested

TCA crate

Trigger board

Front-end

Data Acquisition

D. Lhuillier - AAP 2015 - Arlington VA

15

07/12/2015

• Configuration and data collection done using standard ILL software NOMAD
• Development of low level driver done at LPSC fully operational
• Slow-control, monitoring, alarm system under development

Internal Shielding

D. Lhuillier - AAP 2015 - Arlington VA

16

07/12/2015

• 65 T of lead against external γ-rays
• 6 T Polyethylene against fast neutrons
• B4C layers against thermal neutrons
• Soft Iron + μ Metal layers to shield stray B-field

Muon Veto

Internal shieldings

Magnetic shieldings

Overview

• Seismic study finalized, Fire study still in progress

• Muon veto umbrella to tag cosmic ray induced background

Muon Veto

D. Lhuillier - AAP 2015 - Arlington VA

17

07/12/2015

• Water-Cerenkov detector
• 4x2.6x0.25 m³ water + wavelength shifter (4MU)
• 20 PMTs on the top
• Tyvek diffuser

• Results from prototype
• Excellent overall efficiency 98.5% and stable
• PMTs mapping to reduce sensitivity to γ-rays
• Final detector fabricated and soon delivered

Site Characterization

D. Lhuillier - AAP 2015 - Arlington VA

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07/12/2015

Stereo

Extensive γ, μ and n measurements on site performed in 2014-15:

• Ge, NaI,³He and fast-n detectors inside various shielding
• Data analysis coupled simulation of the detector setups
• MCNPX simulations of the reactor and main neutron lines
• Energy spectrum and location of all sources
• Design of shielding to meet the specifications of <100 Hz in prompt window and 1 Hz in delayed window.

Modular PE shielding

Directionality studies

Deconvoluted γ-spectrum

Complete reactor simulations

Shielding Configuration

D. Lhuillier - AAP 2015 - Arlington VA

19

07/12/2015

• Old “H7” line removed

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• Combination of heavy concrete, lead and B4 barriers to block γ and n fluxes.

STEREO

Shielding Configuration

D. Lhuillier - AAP 2015 - Arlington VA

20

07/12/2015

Neutron absorbers added in neighbor primary casemate

STEREO

Shielding Configuration

D. Lhuillier - AAP 2015 - Arlington VA

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07/12/2015

Last front wall installed in Sept. 2015

10 cm lead + 10 cm PE

STEREO

Shielding Configuration

D. Lhuillier - AAP 2015 - Arlington VA

22

07/12/2015

Final reinforcement of the side wall foreseen this winter.

STEREO

Sensitivity

D. Lhuillier - AAP 2015 - Arlington VA

23

07/12/2015

• 400 ν per day during 300 days

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• Signal/Background = 1.5

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• Detection and reconstruction effects from GEANT4 simulation

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• Neutrino flux uncertainties + 4% norm uncertainty

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• Visible E_e+ > 2 MeV

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• E_n > 5 MeV 🡪 ε_det=60%

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• δE_scale = 2%

New Reference ²³⁵U Spectrum

D. Lhuillier - AAP 2015 - Arlington VA

24

07/12/2015

• 120 000 ν expected
• Highly enriched fuel

🡪 pure 235U fission spectrum

Daya Bay Aug. 2015

RENO Nov. 2015

Caution: RENO normalization?

• Measurement complementary to Double Chooz, Daya Bay and Reno near detectors.

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• Could bring new insight into the deviation at 5 MeV (see Julia’s talk)

5 MeV Bump

D. Lhuillier - AAP 2015 - Arlington VA

25

07/12/2015

• Evolution of the sensitivity when introducing the 5 MeV Bump as a new uncertainty in the predicted spectrum (50% of the amplitude).

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• To first order the oscillation phase is not compatible with an isolated deviation around 5 MeV.

Conclusion

D. Lhuillier - AAP 2015 - Arlington VA

26

07/12/2015

• Sensitivity contours cover the Reactor Anomaly. Emphasis on control of the detector response to control shape distortions.

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• Final design validated by prototypes and seismic studies

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• Several external shielding walls have already been installed

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• Most parts of detector are under fabrication or already delivered, the schedule is now driven by the delivery of some shielding parts and the final safety agreement.

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• The detector integration will take place at LPSC-Grenoble in Feb-March 2016

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• First data expected in summer 2016