Description
Different extensions of the standard model of particle physics, such as braneworld or mirror matter models, predict the existence of a neutron sterile state. Intitially designed to search for a sterile neutrino, the STEREO experiment at the high flux reactor of the Institut Laue-Langevin investigated the possibility for the neutron to swap between active and sterile states using the principle of a passing-through-walls neutron experiment. Reactor neutrons could swap into sterile neutrons, escape the reactor and regenerate into the STEREO detector. A dedicated analysis of the STEREO data showed no evidence for such a mechanism but allowed to improve the upper limit on the swapping probability by a factor of 13 with respect to previous dedicated experiments, to 3.1 × 10^−11 at 95% C.L [1]. The key parameters for this improvement are the neutron flux within the ILL reactor, which is the highest worldwide thanks to the low absorption cross section of heavy water, the shielding against the neutron background and the large active volume of STEREO for the regeneration and detection of hidden neutrons. This result demonstrates that short-baseline reactor neutrino experiments are very well suited for the quest of a neutron sterile state.
[1] H. Almazán et al., Searching for Hidden Neutrons with a Reactor Neutrino Experiment: Constraints from the STEREO Experiment, Phys. Rev. Lett. 128, 061801 (2022).
| Collaboration | STEREO |
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