Physics Beyond Colliders

Physics Beyond Colliders. It is a global study group and conceptual framework, primarily hosted at CERN, dedicated to exploring and developing high-precision, high-intensity experiments that complement the discovery potential of particle colliders like the Large Hadron Collider. The initiative aims to investigate fundamental questions in particle physics and cosmology through alternative methodologies, seeking evidence for phenomena such as dark matter, dark energy, and new forces that may be inaccessible to collider experiments alone. By leveraging existing accelerator complexes and proposing new fixed-target experiments, it represents a strategic pillar in the future of experimental high-energy physics.

● Introduction

The Physics Beyond Colliders initiative was formally launched in 2016, emerging from discussions within the European Strategy for Particle Physics and the broader international community. It operates under the auspices of CERN's Experimental Physics Department, coordinating efforts among theorists and experimentalists from institutions like Fermilab, KEK, and DESY. The program was established recognizing that while machines like the Large Hadron Collider are powerful tools for direct discovery, other frontiers require different techniques. Its foundational report, a key outcome of the 2019 CERN Workshop on Physics Beyond Colliders, outlined a roadmap integrating these efforts with the global particle physics agenda.

● Scientific Motivations

The core motivations stem from unresolved mysteries in the Standard Model and cosmology. A primary driver is the search for ultralight dark matter and wave-like dark matter candidates, such as axions and dark photons, which are poorly probed by high-energy collisions. Another key aim is to perform ultra-precise tests of flavor physics and charge-parity violation to uncover hints of new physics, as pursued by experiments like LHCb and Belle II. Furthermore, the initiative seeks to explore the nature of neutrino masses and their implications via intense beams, connecting to programs at J-PARC and the Deep Underground Neutrino Experiment. These efforts are tightly linked to theoretical work on models like the Minimal Supersymmetric Standard Model and string theory.

● Proposed Experiments and Facilities

The study group evaluates a diverse portfolio of proposed projects, many designed to use CERN's accelerator infrastructure. Notable fixed-target proposals include the Search for Hidden Particles experiment, which would use beams from the Super Proton Synchrotron to hunt for weakly interacting particles. Another is the Gamma Factory, a novel concept to produce intense photon beams using partially stripped ions in the Large Hadron Collider. Projects like the Muon g-2 experiment, with iterations at Fermilab and J-PARC, and the proposed Muon Collider, are also central to the roadmap. Other facilities under consideration include upgrades to the NA62 experiment at CERN and the MATHUSLA detector concept for the High-Luminosity Large Hadron Collider era.

● Complementary Approaches to Collider

Physics These non-collider methods provide essential synergy with frontier colliders. High-intensity experiments can probe extremely small couplings and very light particles in ways that high-energy colliders cannot, offering a complementary search strategy for phenomena predicted by theories like the QCD axion model. Precision measurements of fundamental constants, such as the anomalous magnetic moment of the muon, serve as indirect probes for new particles at mass scales potentially beyond the reach of the Large Hadron Collider. This philosophy of complementarity is also evident in global efforts in gravitational wave astronomy by collaborations like LIGO and Virgo, and in cosmic microwave background studies by the Planck satellite and Simons Observatory.

● Challenges and Future Prospects

Significant challenges include securing funding and beam time in a highly competitive global landscape, and the technical difficulties of achieving unprecedented levels of sensitivity and background suppression. Integrating these diverse projects into a coherent global strategy requires continued coordination through bodies like the International Committee for Future Accelerators and the European Strategy Group. The future prospects of Physics Beyond Colliders are intrinsically tied to the updates of the European Strategy for Particle Physics and the Snowmass Process in the United States. Successful implementation could lead to transformative discoveries in the search for dark sector particles and a deeper understanding of quantum gravity and the early universe, shaping the field for decades.

Category:Particle physics Category:Research projects Category:CERN