In 2020, the update of the European strategy for particle physics (ESPPU) stressed: „A diverse programme that is complementary to the energy frontier is an essential part of the European particle physics Strategy. Experiments in such diverse areas that offer potential high-impact particle physics programmes at laboratories in Europe should be supported, as well as participation in such experiments in other regions of the world.“
In 2022, CERN put in place a process to decide until end of 2023 whether the SPS North Area (NA) beamline TCC8 and experimental cavern ECN3, where currently the NA62 experiment is located, will be upgraded to a High-Intensity (HI) proton facility to realize a high-impact diversity programme. For ECN3, two competing proposals are currently under review:
* To improve the experimental precision on the rare kaon decay K+ --> pi+ nu anti-nu, which has been measured for the first time by NA62, and to measure rare KL decays with high precision, a HI Kaon Experiments (HIKE) programme, building on the NA62 experiment, is proposed to take data over one decade. Besides kaon running, it is foreseen to run a significant portion of time in beam-dump mode to search for feebly-interacting particles (FIPs) produced in the beam dump. Since HIKE is optimized for kaon physics, it is mainly sensitive to FIP production in the very forward direction. Therfore, a second detector for beam-dump mode running is proposed to be installed off-axis, close to the beam-dump target, called SHADOWS, to complement the FIP search sensitivity when running in beam-dump mode.
* In 2014, it was already proposed to build a dedicated HI proton beam-dump facility (BDF) in a new experimental cavern (ECN4) at the SPS NA with the Search for Hidden Particles (SHiP) experiment proposal. While the ESPPU highlighted the BDF as a forerunner in exploring the FIP parameter space, it could not recommend it at that time in light of financial constraints. An alternative location search at CERN concluded that the existing ECN3 was the best location for BDF/ SHiP offering a significant price reduction without compromising the physics sensitivity. The BDF design and the SHiP experiment are optimized for FIP searches in a close-to-zero-background environment and outperform all competing proposals in the target parameter range. The setup contains also a dedicated Scattering-and-Neutrino (SND) detector, the technology of which is already in use in SND@LHC. SND allows to search for scattering of light dark matter particles produced in the beam dump and offers a broad neutrino programme, in particular the first high-statistics tau- and anti-tau neutrino sample.
An overview of the projects will be given with a focus on BDF/SHiP.