A Facility to Search for Hidden Particles (SHiP) at the CERN SPS

A new general purpose fixed target facility is proposed at the CERN SPS accelerator which is aimed at exploring the domain of hidden particles and make measurements with tau neutrinos. Hidden particles are predicted by a large number of models beyond the Standard Model. The high intensity of the SPS 400~GeV beam allows probing a wide variety of models containing light long-lived exotic particles with masses below ${\cal O}$(10)~GeV/c$^2$, including very weakly interacting low-energy SUSY states. The experimental programme of the proposed facility is capable of being extended in the future, e.g. to include direct searches for Dark Matter and Lepton Flavour Violation. The facility will be serviced by a new dedicated beam line branched off the splitter section on the North Area. It is followed by a new target station and a magnetic shield to suppress beam induced background. The proposed orientation of the beam line and the underground complex allows reserving more than 100~m of space beyond the experimental hall to host future extensions of the experimental program. In the first phase, the facility will host a detector to search for hidden particles and a compact tau neutrino detector. The hidden particle detector consists of a long, evacuated decay volume with a magnetic spectrometer, calorimeters and muon detectors at the far end. This allows full reconstruction and particle identification of hidden particle decays. The robustness against various types of background is guaranteed by background taggers and a dedicated timing detector. The tau neutrino detector consists of an emulsion target equipped with tracking in a magnetic field followed by a muon spectrometer. Under nominal conditions the current SPS is capable of providing an integrated total of 2$\cdot$10$^{20}$ protons on target in five years of operation. This allows access to a significant fraction of the unexplored parameter space for the Hidden Sector, at nearly zero background level, with sensitivities which are several orders of magnitude better than previous experiments. The associated tau neutrino detector will allow performing a number of unique measurements with tau neutrinos, including a first direct experimental observation of the anti-tau neutrino interactions. The SHiP facility will provide a unique experimental platform for physics at the Intensity Frontier which is complementary to the searches for New Physics at the Energy Frontier. A discovery of a very weakly interacting Hidden Sector would lead to a dramatic breakthrough in our understanding of particle physics and of the Universe. In addition, it would open up a new field of experimental particle physics, which would benefit from accelerators capable of exceeding the already outstanding performance of the SPS.