# Other science opportunities at the FCC-ee

## TL;DR

The FCC-ee collider offers high-energy physics research and unique opportunities in other scientific fields due to its design and capabilities.

## Contribution

The paper highlights novel scientific opportunities enabled by the FCC-ee beyond its primary physics goals.

## Key findings

- The FCC-ee can produce true muonium and a Bose-Einstein condensate of positronium.
- It can generate high-brightness photon beams down to 0.1 Å wavelengths.
- The collider supports radioactive isotope production and neutron sources via electron or photon beams.

## Abstract

The Future Circular Collider (FCC) integrated programme begins with the FCC-ee, an electron-positron collider, followed by the FCC-hh, a proton–proton collider installed in the same 91 km circumference tunnel near CERN. Spanning 15 years from the mid-to-late 2040s through the early 2060s, the FCC-ee will operate at centre-of-mass energies between approximately 90 and 365 GeV, consistently delivering the highest possible luminosities to four experiments in a sustainable and energy-efficient manner. A key element of its design is top-up injection from a full-energy booster housed in the same 91 km tunnel, along with the world’s most intense positron source and 20 GeV injector linacs. The FCC-ee injector complex, comprising a high intensity positron source, a damping ring, and a linac accelerating electrons and positrons up to 20 GeV, is expected to start operation several years earlier than the booster and the collider. The primary objective of the FCC-ee is its rich High Energy Physics programme based on electron-positron collisions at various centre-of-mass energies (Benedikt et al. in Eur Phys J C 85:1468 10.1140/epjc/s10052-025-15077-x, 2025). In addition, thanks to its large circumference, high beam energy, abundant positron production, and low-emittance beams, the FCC-ee also offers unique opportunities for various fields of physics and science. These include the potential production of true muonium, the creation of a Bose-Einstein condensate of positronium, Compton imaging with high-energy photons, the generation of spatially coherent photon beams, possibly down to 0.1 Åwavelengths—achieving several orders of magnitude higher average and peak brightness than any existing or planned light source—radioactive isotope production, and an electron- or photon-beam-driven neutron source. We present these and other science exploitations of the FCC-ee accelerator complex.