Speaker
Description
The European Spallation Source (ESS), presently under construction in Lund, Sweden, is a multidisciplinary international laboratory that aims to become the world's most powerful pulsed neutron source. At its design performance, it will also be at the "intensity frontier" of particle-physics research and provide unique opportunities to solve open questions about the fundamental building blocks of the universe.
This contribution will focus on one part of the diverse particle-physics efforts at the ESS [1], namely the search for baryon-number violating (BNV) neutron conversion into anti- or "dark" matter by the NNBAR collaboration. Such BNV processes are important assumptions of modern theories to explain experimental findings in disagreement with the standard model(s), but they have yet to be observed in the laboratory.
The first stage of the NNBAR research program, the High Intensity Baryon Extraction and Measurement (HIBEAM) experiment at the fundamental physics beamline of the ESS, is dedicated to the search for neutron oscillations into "sterile" neutrons as members of a hypothetical dark sector of matter [2]. Design criteria for the experimental setup are a low background and a precise control of the magnetic field over a large flight path on the order of 50 meters to amplify oscillations in the proposed conversion mechanism.
In the second stage, the NNBAR experiment will be operated at the large beam port (LBP) of ESS, which was specifically designed to provide an unprecedented neutron flux for neutron-antineutron oscillation searches. In combination with innovative developments in neutron moderation and -guiding technology, it is foreseen to surpass the sensitivity of a pioneering experiment at the Institut Laue Langevin in Grenoble, France [3] by three orders of magnitude. The conversion search also requires the development of a detection system to unambiguously identify the signature 1.9-GeV multi-pion final state of a neutron-antineutron annihilation event on the large detection surface.
Experiments at the scale of the NNBAR program do not only provide unique opportunities, but also pose exciting engineering and safety challenges. Both stages of the NNBAR program are in the design phase, and an extensive simulation effort is being made to optimize all aspects of the experiment operation - from the neutron source to the data analysis. This contribution will give an overview of the goals and discuss the most recent developments.
[1] H. Abele et al., "Particle Physics at the European Spallation Source", arXiv:2211.10396
[2] Z. Berezhiani and L. Bento, "Neutron - mirror neutron oscillations: How fast might they be?" Phys. Rev. Lett. 96 (2006) 081801, doi:10.1103/PhysRevLett.96.081801, arXiv:hep-ph/0507031
[3] M. Baldo-Ceolin, et al., "A New experimental limit on neutron - anti-neutron oscillations", Z. Phys. C 63 (1994) 409–416. doi:10.1007/BF01580321
