Long-lived particles have significant enough lifetimes as to, when produced in collisions, leave distinct signatures in the detectors. Driven by increasingly higher energies, particle colliders are optimized for increasingly heavier particles, which in turn, tend to be short-lived. This makes searches for long-lived particles challenging, usually requiring dedicated methods and hardware to spot them. However, taking upon the challenge brings enormous potential, since these particles feature in a variety of promising new physics models that could answer most of the open questions of the standard model, such as: neutrino masses, Dark Matter, or the matter-antimatter imbalance in the Universe.
With the LHC about to start its last data-taking period before being upgraded to the High-Luminosity LHC, it is time for the international high energy physics community to define the future of collider particle physics. The European Strategy for Particle Physics highlights an e+e- Higgs boson factory as the main priority and as a first step towards a very high-energy future hadron collider.
A staged Future Circular Collider (FCC), consisting of a luminosity-frontier highest-energy electron-positron collider (FCC-ee) followed by an energy-frontier hadron collider (FCC-hh), promises a far-reaching physics program for the post-LHC era. FCC-ee is a precision instrument to study the Z, W, Higgs and top particles, and offers unprecedented sensitivity to signs of new physics. Most of the FCC-ee infrastructure can later be reused for the subsequent hadron collider, FCC-hh.
Crucial physics cases connected to long-lived particles will be accessible at the FCC. The complementarity of the three different stages of the FCC provides unique potential to discover and pin down these particles, and potentially solve long-standing problems of the SM.
This talk will describe the current landscape and possible areas to contribute to in the next few years. Three interesting examples are highlighted: Heavy Neutral Leptons, Hidden Sectors connected to Dark Matter, and exotic Higgs boson decays. The exploration of long-lived particles at the FCC-ee motivates an out-of-the-box experimental optimizations that will also be discussed.
