New Results from STEREO: a Search for a Sterile Neutrino 1eV at - - PowerPoint PPT Presentation

New Results from STEREO: a Search for a Sterile Neutrino ∼1eV at Short Baseline

Laura Bernard

LPSC, Grenoble, France

• n behalf of the STEREO collaboration

Photo: ILL

Spokesperson: David Lhuillier (CEA) Contact: david.lhuillier@cea.fr

The STEREO Collaboration

Photo: Stefan Schoppmann

Motivation: Flux Measurement − → ¯

νe Disappearance at Short Baseline

2011: Re-evaluation of the ¯ νe 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

Laura Bernard, MORIOND, March 19, 2019

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Motivation: Flux Measurement − → Sterile Neutrino Hypothesis

Phys.Rev.D83:073006 (2011)

Introduction of a 4th neutrino adds a mixing with the ¯ νe :

Pνe→νe (Eνe ,L) = 1 - sin2(2θnew) sin2 1.27 ∆m2

new [eV 2]L[km]

Eνe [MeV ]

• Suggested oscillation parameter best fit by RAA :
• ∆m2

new = 2.3 eV2

• sin2(2θnew) = 0.14

3+1 scenario fits better the experimental data points : 3+1ν model 3ν model

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 10

− 1

10 10

1

10

2

10

3

10

4

10

5

10

6

Reactor To Detector Distance(m)

R = Nexperimental / Npredicted

Reactor

6 % deficit

anomaly anomaly anomaly Atmospheric Solar Laura Bernard, MORIOND, March 19, 2019

2/18

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 ¯

νe energy spectrum

Laura Bernard, MORIOND, March 19, 2019

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Experimental Site

ILL research facility, Grenoble, France

Research reactor core ∼ 58 MWth → 1019 ¯ νe s−1

• Compact core (∅40cm × 80cm)
• Highly enriched 235U (93%)
• Short baseline measurement:

9.4m < Lcore < 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)

Laura Bernard, MORIOND, March 19, 2019

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The STEREO Experiment

arXiv:1804.09052 (2018)

Gamma-catcher

scintillator liquid (no Gd)

Designed to: 1- Probe the RAA1 region by measuring oscillation-driven distortions of the ¯ νe energy

• f the distance

− → Independent from predicted energy spectrum 2- Provide a measurement of a pure 235U ¯ νe energy spectrum