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

Latest Results of the Neutrino Flux and Spectrum from Daya Bay Jianrun Hu On behalf of the Daya Bay Collaboration Institute of High Energy Physics, China Rencontres de Moriond, March 21 st , 2019

Reactor Antineutrino • Electron antineutrinos produced in commercial nuclear reactor cores: • Mainly from fission fragments of the fission isotopes 235 U , 238 U , 239 Pu , and 241 Pu . Inverse 𝛾 decay (IBD): • Prompt: 𝐹 𝑞rompt = 𝐹 𝑤 − 0.8𝑁𝑓𝑊 • Delayed: nGd (~8 MeV) 2

Antineutrino Flux and Spectrum • Flux comparison between data and prediction: • ~5% deficit in data! • Reactor antineutrino anomaly ( RAA ). R data/pred = 0.952 ± 0.014(exp.) ± 0.023(model) σ f = (5.91 ± 0.09) × 10 −43 cm 2 /fission arXiv:1808.10836 3

Antineutrino Flux and Spectrum • Flux comparison between data and prediction: • ~5% deficit in data! • Reactor antineutrino anomaly ( RAA ). • Shape comparison: • Global deviation: 2.9 𝝉 . • A bump is found ( 4.4 𝝉 ) between 4~6 MeV. Chinese Physics C, 2017, 41(1) 4

Antineutrino Flux and Spectrum • Flux comparison between data and prediction: • ~5% deficit in data! • Reactor antineutrino anomaly ( RAA ). • Shape comparison: • Global deviation: 2.9 𝝉 . Grouping • A bump is found ( 4.4 𝝉 ) between 4~6 MeV. • Fuel evolution: 5

Antineutrino Flux and Spectrum U235: 7.8% deficit! • Flux comparison between data and prediction: • ~5% deficit in data! • Reactor antineutrino anomaly ( RAA ). • Shape comparison: • Global deviation: 2.9 𝝉 . • Pu239: A bump is found Consistent. ( 4.4 𝝉 ) between 4~6 MeV. • Fuel evolution: • U235: may be PRL.118.251801 primarily responsible for Disfavor equal deficit (2.8 𝜏 ) and RAA . Pu239-only deficit (3.2 𝜏 ). 6

Antineutrino Flux and Spectrum • Flux comparison • Key improvements: between data and ① More statistics, (IBD candidates): prediction: ~1.2 million → ~3.5 million. • ~5% deficit in data! ② Improved uncertainty of • Reactor antineutrino nonlinearity energy model: ~1% anomaly ( RAA ). → ~0.5%. • Shape comparison: • Global deviation: 2.9 𝝉 . • A bump is found ( 4.4 𝝉 ) between 4~6 MeV. • Fuel evolution: • U235: may be primarily responsible for RAA . arXiv:1902.08241 7

Antineutrino Flux and Spectrum • Flux comparison between data and prediction: • ~5% deficit in data! Previous • Reactor antineutrino uncertainty: anomaly ( RAA ). ~2% • Shape comparison: • Global deviation: 2.9 𝝉 . Improve • A bump is found ( 4.4 𝝉 ) between 4~6 MeV. • Fuel evolution: Updated • uncertainty: U235: may be ~1% primarily responsible for RAA . 8

Antineutrino Flux and Spectrum • Flux comparison Shape comparison between data and prediction: • ~5% deficit in data! • Reactor antineutrino anomaly ( RAA ). • Shape comparison: • Global deviation: 2.9 𝝉 . • A bump is found ( 4.4 𝝉 ) between 4~6 MeV. • Fuel evolution: • U235: may be primarily responsible for RAA . 9

Antineutrino Flux and Spectrum • Flux comparison • Shape comparison: between data and • Global deviation: 5.3 𝝉 . prediction: • A bump is found ( 6.3 𝝉 ) • ~5% deficit in data! between 4~6 MeV. • Reactor antineutrino anomaly ( RAA ). • Shape comparison: • Global deviation: 2.9 𝝉 . • A bump is found ( 4.4 𝝉 ) between 4~6 MeV. • Fuel evolution: • U235: may be primarily responsible for RAA . 10

Antineutrino Flux and Spectrum • Flux comparison • Shape comparison: between data and • Global deviation: 5.3 𝝉 . prediction: • A bump is found ( 6.3 𝝉 ) • ~5% deficit in data! between 4~6 MeV. • Reactor antineutrino anomaly ( RAA ). • Shape comparison: • Global deviation: Incorrect 2.9 𝝉 . model? RAA and • A bump is found spectral ( 4.4 𝝉 ) between distortion New physics? 4~6 MeV. (Sterile • Neutrino … ) Fuel evolution: • U235: may be primarily responsible for RAA . 11

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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 ones of Pu are increasing. Contribution from different isotopes to the total neutrino flux. 14

• (A) All signals Prompt-delayed pairs: • (B) Flasher removal • 1 μ s < Δ t < 200 μ s • (C) Water-pool muon veto • 0.7 MeV < E prompt < 12 MeV • (D) Coincidence pair • 6 MeV < E delayed < 12 MeV • (E) AD muon veto n capture on H n capture on Gd Phys. Rev. D 95 , 072006 (2017) 15

• Water Cherenkov detector and RPCs: • Antineutrino detectors (ADs): “T hree- zone” cylindrical • S hield the ADs from natural • radioactivity and neutrons modules • Veto cosmic-ray muons Energy resolution: 𝜏 𝐹 / E ≅ 8.5%/ √ E[MeV] Gd-doped 192 8 ’’ Liquid LS PMTs Scintillator (GdLS) Mineral Oil NIM A 811 , 133 (2016) NIM A 773 , 8 (2015) 16

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𝜉 𝑓 Flux Prediction Reactor ҧ • Summation (ab initio) method • > 6000 decay branches • Missing data in the nuclear database • ~30% forbidden decays • ~ 10% uncertainty • Conversion method • Convert ILL measured 235 U, 239 Pu and 241 Pu 𝛾 spectra to ҧ 𝜑 𝑓 with >30 virtual 𝛾 -decay branches • Old: ILL + Vogel ( 238 U) model (1980s) • New: Huber + Mueller ( 238 U) model (2011) • ~ 2.4% uncertainty 19

arXiv: 1902.08241 • Converts reconstructed positron energy to its true energy Two calibration campaigns: • Direct measurement of electronics nonlinearity by a full FADC system • Better understanding of the optical shadowing of γ -source enclosures Scintillator Electronics A direct measurement of the nonlinearity nonlinearity electronics nonlinearity 12 B spectrum Full nonlinearity Uncertainty of absolute energy scale is reduced to ~0.5% 20

Prompt spectrum and background of EH1 21