Following a decision taken during the June session of the CERN Council to launch a technical design study for a new high-intensity physics programme at CERN’s North Area, a recommendation for experiment(s) that can best take advantage of the intense proton beam on offer is expected to be made by the end of 2023.
The design study concerns the extraction of a high-intensity beam from the Super Proton Synchrotron (SPS) to deliver up to a factor of approximately 20 more protons per year to ECN3 (Experimental Cavern North 3). It is an outcome of the Physics Beyond Colliders (PBC) initiative, which was launched in 2016 to explore ways to further diversify and expand the CERN scientific programme by covering kinematical domains that are complementary to those accessible to high-energy colliders, with a focus on programmes for the start of operations after Long Shutdown 3 towards the end of the decade.
CERN is confident in reaching the beam intensities required for all experiments
To employ a high-intensity proton beam at a fixed-target experiment in the North Area and to effectively exploit the protons accelerated by the SPS, the beam must be extracted slowly. In contrast to fast extraction within a single turn of the synchrotron, which utilises kicker magnets to change the path of a passing proton bunch, slow extraction gradually shaves the beam over several hundred thousand turns to produce a continuous flow of protons over a period of several seconds. One important limitation to overcome concerns particle losses during the extraction, foremost on the thin electrostatic extraction septum of the SPS but also along the transfer line leading to the North Area target stations. An R&D study backed by the PBC initiative has shown that it is possible to deflect the protons away from the blade of the electrostatic septum using thin, bent crystals. “Based on the technical feasibility study carried out in the PBC Beam Delivery ECN3 task force, CERN is confident in reaching the beam intensities required for all experiments,” says ECN3 project leader Matthew Fraser.
Currently, ECN3 hosts the NA62 experiment, which searches for ultra-rare kaon decays as well as for feebly-interacting particles (FIPs). Three experimental proposals that could exploit a high-intensity beam in ECN3 have been submitted to the SPS committee, and on 6 December the CERN research board is expected to decide which should be taken forward. The High-Intensity Kaon Experiment (HIKE), which requires an increase of the current beam intensity by a factor of between four and seven, aims to increase the precision on ultra-rare kaon decays to further constrain the Cabibbo–Kobayashi–Maskawa unitarity triangle and to search for decays of FIPs that may appear on the same axis as the dumped proton beam. Looking for off-axis FIP decays, the SHADOWS (Search for Hidden And Dark Objects With the SPS) programme could run alongside HIKE when operated in beam-dump mode. Alternatively, the SHiP (Search for Hidden Particles) experiment would investigate hidden sectors such as heavy neutral leptons in the GeV mass range and also enable access to muon- and tau-neutrino physics in a dedicated beam-dump facility installed in ECN3.
The ambitious programme to provide and prepare the high-intensity ECN3 facility for the 2030s onwards is driven in synergy with the North Area consolidation project, which has been ongoing since Long Shutdown 2. Works are planned to be carried out without impacting the other beamlines and experiments in the North Area, with first beam commissioning of the new facility expected from 2030.
“Once the experimental decision has been made, things will move quickly and the experimental groups will be able to form strong collaborations around a new ECN3 physics facility, upgraded with the help of CERN’s equipment and service groups,” says Markus Brugger, co-chair of the PBC ECN3 task force.