New Results from STEREO: a Search for a Sterile Neutrino ∼ 1eV at Short Baseline Laura Bernard LPSC, Grenoble, France on behalf of the STEREO collaboration
Spokesperson: David Lhuillier (CEA) Contact: david.lhuillier@cea.fr Photo: ILL Photo: Stefan Schoppmann The STEREO Collaboration
Motivation: Flux Measurement − → ¯ ν e Disappearance at Short Baseline 2011: Re-evaluation of the ¯ ν e reactor flux prediction → Reactor Antineutrino Anomaly − All reactor short-baseline experiments are observing a deficit ( ∼ 6%) → confirmed by recent accurate measurements from Daya Bay, RENO & Double Chooz 1/18 Laura Bernard, MORIOND, March 19, 2019
Motivation: Flux Measurement − → Sterile Neutrino Hypothesis Phys.Rev.D83:073006 (2011) Introduction of a 4th neutrino adds a mixing with the ¯ ν e : P ν e → ν e (E ν e ,L) = 1 - sin 2 (2 θ new ) sin 2 � 1 . 27 ∆ m 2 new [ eV 2 ] L [ km ] � E ν e [ MeV ] Suggested oscillation parameter best fit by RAA : • ∆ m 2 new = 2.3 eV 2 • sin 2 (2 θ new ) = 0.14 3+1 scenario fits better the experimental data points : 3 ν R = Nexperimental / Npredicted 1.1 model 6 % 1 de fi cit 3+1 ν 0.9 model 0.8 0.7 0.6 Reactor Atmospheric Solar 0.5 anomaly anomaly anomaly 0.4 − 1 0 1 2 3 4 5 6 10 10 10 10 10 10 10 10 Reactor To Detector Distance(m) 2/18 Laura Bernard, MORIOND, March 19, 2019
Motivation: Spectral Distortions → Isotopes Contributions & Nuclear Models − Several experiments revealed a "bump" around 5 MeV w.r.t. predicted spectrum • Could be linked to underestimation of certain isotopes of uranium/plutonium • Can not explain the total deficit Double Chooz Collaboration (De Kerret, H. et al.) arXiv:1901.09445 [hep-ex] → Studies of decorrelation of isotopes − contributions at commercial reactors In conclusion: • Sterile neutrino ? • Wrong prediction ? → Need dedicated measurements: − • Confirm or rule out sterile ν hypothesis • Constrain the ¯ ν e energy spectrum 3/18 Laura Bernard, MORIOND, March 19, 2019
Experimental Site ILL research facility, Grenoble, France Research reactor core ∼ 58 MW th → 10 19 ¯ ν e s − 1 • Compact core ( ∅ 40cm × 80cm) • Highly enriched 235 U (93%) • Short baseline measurement: 9.4m < L core < 11.2m Challenging mitigation of the background • γ and neutron background from neighboring experiments • Surface-level experiment (15 m.w.e thanks to water channel) 4/18 Laura Bernard, MORIOND, March 19, 2019
The STEREO Experiment arXiv:1804.09052 (2018) Gamma-catcher scintillator liquid (no Gd) Designed to: 1- Probe the RAA 1 region by measuring oscillation-driven distortions of the ¯ ν e energy of the distance → Independent from predicted energy spectrum − 2- Provide a measurement of a pure 235 U ¯ ν e energy spectrum
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