A SHiP to explore new routes
SHiP (Search for Hidden Particles) is a proposed new facility for CERN's SPS accelerator. Its challenging goals include a direct search for hidden non-Standard-Model particles. Predicted by a large number of theoretical models, such particles could have slipped under the radar of the LHC experiments because of their specific features. In its first symposium held at CERN on 2 July, SHiP scientists showed the broader scientific community how they plan to unveil the hidden world.
The SHiP experiment is designed to be installed next to the SPS North Area.
Powerful accelerators like the LHC allow physicists to explore extensively the primordial phenomena at energy densities equivalent to those that existed just a few moments after the Big Bang. In this way, thanks to the high precision of the LHC experiments, scientists have been able to comprehensively confirm the predictions of the Standard Model (SM), including the existence of a Higgs boson. However, new physics – particles and phenomena that would explain the observed shortcomings of the SM and would also account for dark matter (which makes up 25% of the Universe) and dark energy (70% of the Universe) – seems to hide in as-yet unexplored regions.
Several theoretical models predict the existence of particles that would interact very weakly with SM particles, would be very rare and would typically have very long lifetimes. These particles, collectively called “hidden particles”, are the target of the newly proposed SHiP experiment. “A discovery of a very weakly interacting non-SM particle would lead to a dramatic breakthrough in our understanding of particle physics and the Universe,” explains Andrei Golutvin, SHiP Spokesperson. “The SHiP experiment aims to search for such exotic particles, including heavy neutral leptons, dark photons, light scalars, supersymmetric particles and axion-like particles.”
Designed to be installed next to the SPS North Area, the SHiP facility would be housed in a 120 m long and 20 m wide underground hall, which would follow a dedicated 150 m beam extraction line and a target complex on the Prévessin site. The SM particles produced when the protons from the SPS hit the SHiP target would start to interact and decay according to their respective couplings. However, given their very weak coupling, the hidden particles would continue to fly and would reach the SHiP apparatus, where they would decay and produce detectable particles.
Overview of the SHiP facility.
The accurate identification of a hidden particle candidate is only possible if the background can be suppressed to an unprecedented level. The target is a key element in the SHiP setup. “In order to minimise the neutrino background, the proposed target is designed using titanium-zirconium doped molybdenum, a material with a short nuclear interaction length and with dimensions that contain the proton shower,” explains Richard Jacobsson, who is coordinating the implementation of the detector and the facility. “Secondly, a 50 m long active shield based on magnetic sweeping deflects the muon flux away from the detector decay volume. A large contribution to the background suppression also comes from the slow extraction of the SPS proton beam, which allows us to dilute the 2.6 MW of beam power deposited on the target per spill and to significantly reduce the risk of background due to combinations of residual particles forming fake decay vertices.”
About 200 scientists from 14 countries worldwide have joined the SHiP effort so far. SHiP is currently under review by the SPS Committee, which will go on into the autumn. This week, the collaboration invited the wider scientific community to discuss the scientific case in a symposium held at CERN. “We were very encouraged by the discussions raised by the scientists who attended the symposium,” says Golutvin. “We are now confidently looking forward to the next phases of the project's feasibility assessment process.”
