Speaker
Description
The European Spallation Source (ESS), currently under construction in Lund, Sweden, will provide the most intense pulsed neutron beam in the world. To make use of this unique infrastructure, the two-stage HIBEAM/NNBAR program [1,2] proposes to use neutron beamlines for precision studies of fundamental symmetries. While one of its principal goals is the first search in more than three decades for free neutron-antineutron oscillations, the HIBEAM beamline is envisioned for a broader program that also includes a newly proposed search for ultralight axion-like particles (ALPs) [3].
With the support of the Swedish Foundation for Strategic Research and Swedish Research Council, the collaboration is developing a 10-meter long dual-layer mumetal magnetic shield along with a coil system for Ramsey interferometry. In parallel, ongoing efforts aim to optimise the neutron optics, polarisation system and neutron detector for improved experimental performance and operational reliability. Informed by finite-element magnetostatics simulations and spin dynamics simulations, the design of the magnetic shield and its mechanical support is nearing completion, while ensuring consistency with ESS engineering and radiation safety constraints. Therefore, the procurement phase is commencing and the shield will thereafter be characterised and used in fundamental physics experiments.
In this talk, I will review the physical motivation behind searches for dark matter and axion-like particles. I will then describe the experimental setup in detail and outline the ongoing work on beamline design, with emphasis on magnetic field control, detector design and simulation-driven performance studies.
[1] V. Santoro et al. J. Phys. G: Nucl. Part. Phys. 52, 040501 (2025).
[2] V. Santoro et al. JNR 25(3-4):315 (2024).
[3] P. Fierlinger et al. Phys. Rev. Lett. 133, 181001 (2024).