Free Neutron Oscillations Searches

The European Spallation Source ESS, presently under construction, in Lund, Sweden, is a multi-disciplinary international laboratory. It will operate the world's most powerful pulsed neutron source.  Taking advantage of the unique potential of the ESS, the NNBAR collaboration proposed a two-stage program of experiments to perform high precision searches for neutron conversion in a range of baryon number violation (BNV) channels culminating in an ultimate sensitivity increase for  neutron → antineutron  oscillations of three orders of magnitude over the previously attained limit obtained at the Institut Laue-Langevin ILL . The first stage of this program HIBEAM (High Intensity Baryon Extraction and Measurement) will employ the ESS fundamental physics beamline.  This stage focuses principally on searches for neutron conversion to sterile neutrons n'  that would belong to a ``dark" sector.

The second stage, NNBAR, will exploit a large beam port, specifically designed in the ESS target station monolith for this experiment, to deliver the maximum possible neutron flux and search directly for  neutron→ antineutron  oscillations. The HighNESS project, a 3 MEuro Research and Innovation Action within the EU Horizon 2020 program is now underway for the design of the ESS second neutron source which will be optimized to boost the performance of the NNBAR experiment. The 2020 Update for the European Strategy for Particle Physics explicitly highlights the need for programs at the so called intensity frontier at other European laboratories together with the energy frontier research at CERN. In this context, a fundamental physics program at the ESS, with a series of measurements and searches with unique potential and sensitivity represents a compelling possibility which should not be missed. This talk will focus on the HighNESS program and the ongoing developments in the NNBAR collaboration.