Nuclear Physics Division

Reactor antineutrino anomalies are a decade-long puzzle in neutrino physics. They are manifested by deviations of the order of a few percent between measurements and predictions. These deviations have been observed in the number of antineutrinos measured by more than a dozen experiments at nuclear reactors, and in the shape of the kinetic energy distributions by the seven most recent ones. They could have been the way to a new physics beyond the standard model, but the recent experiments, including the STEREO experiment carried by IRFU, have closed this door.

In a work just published in Physical Review Letter [1], a team of physicists from IRFU and the Laboratoire National Henri Becquerel of DRT have shown that these anomalies could come from biases in the measurements of fission electrons used as a reference for the prediction. They have developed a beta strength function  model to reduce the biases in the calculation of the energy spectra of electrons from fission of fissile reactor nuclei. The two "anomalies" on the antineutrino flux and the "bump" at 5 MeV in the antineutrino energy spectrum are now reproduced by their model. This allows to propose an explanation to solve an enigma of more than 10 years.

The final piece of a longstanding adventure started in 2014 with an experiment led by Irfu and RIKEN Nishina Center has been set with the publication of a paper containing the comparative study of dineutron correlation in ¹¹Li, ¹⁴Be and ¹⁷B [1]. This paper published in Phys. Lett. B completes a series of publications on the topic [2,3] issued from the same experiment using the MINOS device designed and built at Irfu. It suggests that such kind of correlations is a universal feature of Borromean halo nuclei.