Speaker
Description
The FINESSE (Fundamental Interactions with Neutrons at ESS) programme is a proposal for a versatile beamline at the European Spallation Source dedicated to fundamental particle physics. Building on the concept previously developed under the HIBEAM/NNBAR programme, FINESSE extends and generalises this approach into a multi-purpose facility combining high-flux and low-background capabilities within a single instrument.
The beamline is based on an exchangeable guide concept, enabling two complementary operating modes: a high-flux configuration optimised for flux-limited experiments such as neutron--antineutron oscillation searches, axion-like particle searches, and neutron charge measurements; and a low-background configuration designed for precision measurements, including neutron decay studies and electric dipole moment (EDM) experiments.
FINESSE fully exploits the unique pulse structure of ESS and integrates advanced neutron optics, shielding, and magnetic-field control within a unified design.
With its broad scientific scope and staged implementation strategy, FINESSE represents a discovery-class facility capable of delivering a world-leading experimental programme in fundamental physics over the full lifetime of ESS.
The second stage, NNBAR, will exploit a large dedicated beam port in the ESS target station monolith. Its goal is to improve the current $n \rightarrow \bar{n}$ sensitivity by three orders of magnitude compared to the previous limit set at the Institut Laue-Langevin (ILL). The observation of neutron--antineutron oscillations, which violate baryon number $\mathcal{B}$ by two units, would have profound implications for fundamental physics, including the origin of the matter--antimatter asymmetry, the unification of forces, and the nature of neutrino masses.
To achieve this sensitivity, NNBAR will employ a state-of-the-art annihilation detector, high-performance magnetic shielding, advanced neutron optics, and a moderator system optimised to maximise the cold neutron flux. The Conceptual Design Report for the experiment was developed within the HighNESS project, funded by the European Union Horizon 2020 programme.
Together, FINESSE and NNBAR establish a coherent long-term strategy for fundamental neutron physics at ESS, combining discovery potential with precision measurements within a single, scalable infrastructure. This talk will present an overview of the two experiments, their current status, and the main technical challenges.