The First Particle Physics Experiment at the ESS: Search for Axion-like Particles at the HIBEAM Beamline

The European Spallation Source (ESS) in Lund will be the world’s brightest neutron source.

As such, it opens a discovery window at the intensity frontier for phenomena beyond the Standard Model of particle physics. This application proposes a search with early ESS data for axion-like particles (ALPs) coupling to neutrons.

The sensitivity improvement is up to four orders of magnitude compared to the current best laboratory experiments and by an order of magnitude compared with more indirect astrophysical bounds.

ALPs are a well-motivated and topical solution to the dark matter problem, a long-standing open question in modern physics.The presence of ALPs can appear as a pseudo-magnetic field and thus change the Larmor frequency in a magnetically controlled region. A Ramsey set-up is used to search for this effect.

This search is enabled by earlier investments which were made by several Swedish funding agencies (including VR) and the ESS. Investments were made in the HIBEAM beamline design and in neutron extraction and magnetics infrastructure.

The search would be the first fundamental physics experiment at the ESS.Finally, the proposed work would be carried out as part of the HIBEAM/NNBAR project for the ESS. HIBEAM/NNBAR is a Swedish-led initiative to bring a fundamental particle physics program to the ESS. Despite the Swedish investment in the ESS, there are no instruments/beamlines under Swedish scientists’ leadership.

This application helps remedy this omission.