SHiP – Search for Hidden Particles
The Search for Hidden Particles (SHiP) experiment is a new general-purpose experiment at the intensity frontier of particle physics, currently under preparation at CERN. Its primary goal is to search for new, very weakly interacting particles that may explain some of the outstanding mysteries of fundamental physics, including the nature of dark matter, the origin of neutrino masses, and the matter-antimatter asymmetry of the Universe.
Unlike experiments at the energy frontier, which aim to produce new heavy particles in high-energy collisions, SHiP exploits the enormous intensity of the CERN Super Proton Synchrotron (SPS) to search for lighter particles with extremely small couplings to known matter. Such particles, often referred to as feebly interacting particles (FIPs), could have escaped detection in previous experiments. Prominent theoretical candidates include heavy neutral leptons, dark photons, dark scalars, axion-like particles, and light dark matter.
The SHiP experiment at CERN
SHiP was approved in 2024 for the new High-Intensity ECN3 (HI-ECN3) facility at CERN. A 400 GeV/c proton beam from the SPS will be directed onto a thick target, producing large numbers of secondary particles, particularly charmed and beauty hadrons. Their decays may produce new weakly interacting particles, which can subsequently be detected through their visible decays or scattering interactions.
The facility is designed to deliver approximately 4 × 1019 protons on target per year, corresponding to a total of 6 × 1020 protons on target over 15 years of operation. The experiment is currently in its Technical Design Report (TDR) phase, with the detector TDRs planned for 2027. A staged installation and commissioning programme is foreseen, with first data taking currently targeted for the early 2030s.
The experimental setup combines an intense proton target, a hadron absorber and an active magnetic muon shield with two complementary detector systems: the Scattering and Neutrino Detector (SND) and the Hidden Sector Decay Spectrometer (HSDS).
The HSDS searches for long-lived new particles that decay into visible Standard Model particles inside a large, helium-filled decay volume. Tracking detectors, a magnetic spectrometer, precision timing detectors, calorimeters, and background rejection systems allow the reconstruction of rare decay signatures.
The SND, located upstream of the decay spectrometer, searches for light dark matter through scattering interactions and studies the intense neutrino flux produced in the target. In particular, SHiP will provide unprecedented opportunities to investigate tau neutrinos and antineutrinos, which remain the least precisely studied neutrino flavour.
Scattering and Neutrino Detector
The Scattering and Neutrino Detector combines a high-granularity silicon-tungsten calorimeter (SHGC) with a magnetised tracking calorimeter (SMTC). The SHGC consists of tungsten absorber plates interleaved with high-resolution silicon sensors. Its fine spatial granularity enables the reconstruction of particle interaction vertices, charged-particle tracks, and electromagnetic showers.
The downstream SMTC uses magnetised iron absorbers together with scintillating detectors to measure hadronic energy and reconstruct muon tracks, including their momentum and electric charge. Together, these detector systems provide the kinematic and topological information needed to identify neutrino interactions and distinguish potential dark matter scattering signals from Standard Model backgrounds.
A central challenge is the identification of light dark matter scattering off electrons, which can produce a single energetic electron without additional activity at the interaction vertex. The combination of precise tracking, vertex reconstruction, and calorimetry is essential for suppressing backgrounds from neutrino interactions.
Our contributions: detector development
At the University of Siegen, we contribute to the design and development of the SHiP Scattering and Neutrino Detector, with a particular focus on the silicon-tungsten high-granularity calorimeter. Our work includes detector optimisation, simulation studies, prototype development, and the preparation of laboratory and test-beam measurements.
The SHGC combines the high density and short radiation length of tungsten with the excellent spatial resolution of silicon sensors. Optimising the absorber thickness, sensor segmentation, and overall detector geometry requires balancing detector mass, tracking and vertexing performance, energy resolution, and technological constraints.
Our activities contribute to the detector design and performance studies for the 2027 Technical Design Report, followed by the development and validation of detector demonstrators and prototypes.
Our contributions: simulation and physics software
The Siegen group also plays a leading role in the development of simulation and physics software for SHiP. The experiment uses the FairShip software framework for detailed detector simulation, event generation, reconstruction, and physics studies. An accurate description of the experimental geometry and detector response is essential for predicting the sensitivity to new particles and understanding the expected backgrounds.
Our current work includes the modernisation of the SHiP software environment, the development of detector geometries, and advanced reconstruction algorithms. In particular, we are working on the integration of the ACTS tracking toolkit for charged-particle track reconstruction and vertexing, as well as the development of modern approaches to detector geometry description and simulation.
These developments aim to provide a flexible and maintainable software infrastructure for detector optimisation, large-scale Monte Carlo production, and the eventual analysis of SHiP data. They also benefit from common software developments across particle physics experiments.
Physics studies and sensitivity
In addition to detector and software development, our group participates in simulation-based studies of the SHiP physics potential. These include the reconstruction and identification of neutrino interactions, light dark matter scattering, and the optimisation of detector performance for rare-event searches.
The exceptionally large flux of neutrinos produced by the proton beam dump will allow detailed studies of neutrino interactions, including tau-neutrino cross sections and neutrino-induced charm production. The complementary signatures of visible decays and scattering interactions give SHiP sensitivity to a broad range of new physics models that are difficult to probe at collider experiments.
Previous work: SHiP-charm
Our earlier contributions to SHiP include studies of charm production in a thick target through the SHiP-charm experiment. Precise knowledge of charm production is important for predicting the fluxes of heavy neutral leptons and neutrinos expected at SHiP. The SHiP-charm programme included a dedicated test run in 2018, combining nuclear emulsions and electronic tracking detectors to reconstruct particle interactions and decays.
Outlook
With the approval of SHiP and the development of the HI-ECN3 facility, the experiment has entered a new phase of detailed detector design, prototyping, and preparation for construction. The current priority is the completion of the Technical Design Reports, followed by detector demonstration, test-beam validation, and preparation for installation and commissioning.
Our research in Siegen combines expertise in silicon detector technologies, calorimetry, particle reconstruction, and scientific software to contribute to this programme. SHiP offers an exciting opportunity to explore new physics at the intensity frontier while advancing detector technologies and computational methods for future particle physics experiments.