and Spectrum from Daya Bay Jianrun Hu On behalf of the Daya Bay - - PowerPoint PPT Presentation

Jianrun Hu

On behalf of the Daya Bay Collaboration

Latest Results of the Neutrino Flux and Spectrum from Daya Bay

Institute of High Energy Physics, China Rencontres de Moriond, March 21st, 2019

Reactor Antineutrino

• Electron antineutrinos produced in commercial nuclear

reactor cores:

• Mainly from fission fragments of the fission isotopes 235U, 238U,

239Pu, and 241Pu.

2 Inverse 𝛾 decay (IBD):

• Prompt: 𝐹𝑞rompt = 𝐹𝑤 − 0.8𝑁𝑓𝑊
• Delayed: nGd (~8 MeV)

Antineutrino Flux and Spectrum

3

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA). Rdata/pred = 0.952 ± 0.014(exp.) ± 0.023(model) σf = (5.91± 0.09) ×10−43 cm2/fission arXiv:1808.10836

Antineutrino Flux and Spectrum

4 Chinese Physics C, 2017, 41(1)

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

Antineutrino Flux and Spectrum

5

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA). Grouping

• Fuel evolution:

Antineutrino Flux and Spectrum

6

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

• Fuel evolution:
• U235: may be

primarily responsible for RAA.

PRL.118.251801 U235: 7.8% deficit! Pu239: Consistent.

Disfavor equal deficit (2.8𝜏) and Pu239-only deficit (3.2𝜏).

Antineutrino Flux and Spectrum

7

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

• Fuel evolution:
• U235: may be

primarily responsible for RAA.

• Key improvements:

① More statistics, (IBD candidates): ~1.2 million → ~3.5 million. ② Improved uncertainty of nonlinearity energy model: ~1% → ~0.5%.

arXiv:1902.08241

Antineutrino Flux and Spectrum

8

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

• Fuel evolution:
• U235: may be

primarily responsible for RAA.

Previous uncertainty: ~2% Updated uncertainty: ~1% Improve

Antineutrino Flux and Spectrum

9

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

• Fuel evolution:
• U235: may be

primarily responsible for RAA.

Shape comparison

Antineutrino Flux and Spectrum

10

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

• Fuel evolution:
• U235: may be

primarily responsible for RAA.

• Shape comparison:
• Global deviation: 5.3𝝉.
• A bump is found (6.3𝝉)

between 4~6 MeV.

Antineutrino Flux and Spectrum

11

• Shape comparison:
• Global deviation:

2.9𝝉.

• A bump is found

(4.4𝝉) between 4~6 MeV.

• Flux comparison

between data and prediction:

• ~5% deficit in data!
• Reactor antineutrino

anomaly (RAA).

• Fuel evolution:
• U235: may be

primarily responsible for RAA.

• Shape comparison:
• Global deviation: 5.3𝝉.
• A bump is found (6.3𝝉)

between 4~6 MeV. RAA and spectral distortion Incorrect model? New physics? (Sterile Neutrino…)

12

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Reactor Antineutrino Production

• Electron antineutrinos can be produced in commercial nuclear reactor

cores, as neutron-rich fission fragments of the fission isotopes U235, U238, Pu239, and Pu241 beta decay.

• As the fuel burning, the fission fraction of U235 is decreasing, while the
• nes of Pu are increasing.

14 Contribution from different isotopes to the total neutrino flux.

• (A) All signals
• (B) Flasher removal
• (C) Water-pool muon veto
• (D) Coincidence pair
• (E) AD muon veto

Prompt-delayed pairs:

• 1 μs < Δt < 200 μs
• 0.7 MeV < Eprompt < 12 MeV
• 6 MeV < Edelayed < 12 MeV

n capture on Gd n capture on H

• Phys. Rev. D 95, 072006 (2017)

15

Gd-doped Liquid Scintillator (GdLS) LS

NIM A 811, 133 (2016)

Energy resolution: 𝜏𝐹/E ≅ 8.5%/√E[MeV] 192 8’’ PMTs

• Antineutrino detectors (ADs):
• “Three-zone” cylindrical

modules

NIM A 773, 8 (2015)

• Water Cherenkov detector and RPCs:
• Shield the ADs from natural

radioactivity and neutrons

• Veto cosmic-ray muons

Mineral Oil 16

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Reactor ҧ 𝜉𝑓 Flux Prediction

• Summation (ab initio) method
• > 6000 decay branches
• Missing data in the nuclear database
• ~30% forbidden decays
• ~ 10% uncertainty

19

• Conversion method
• Convert ILL measured 235U, 239Pu

and 241Pu 𝛾 spectra to ҧ 𝜑𝑓 with >30 virtual 𝛾-decay branches

• Old: ILL + Vogel (238U)

model (1980s)

• New: Huber + Mueller (238U)

model (2011)

• ~ 2.4% uncertainty

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• Converts reconstructed positron energy to its true energy

Full nonlinearity Scintillator nonlinearity

Uncertainty of absolute energy scale is reduced to ~0.5%

A direct measurement of the electronics nonlinearity

Two calibration campaigns:

• Direct measurement of electronics nonlinearity by a full FADC system
• Better understanding of the optical shadowing of γ-source enclosures

Electronics nonlinearity

12B spectrum

arXiv: 1902.08241

Prompt spectrum and background of EH1

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