Physics Opportunities with the Gamma Factory

We are delighted to introduce to the readership of Annalen der Physik this special issue, which comes in the wake of a workshop with the same title that was held virtually at the Mainz Institute for Theoretical Physics in November–December 2020. The Gamma Factory initiative, being developed within the Physics Beyond Colliders framework, proposes to create novel research tools at CERN by producing, accelerating, and storing highly relativistic, partially stripped ion beams in the Super Proton Synchrotron and the Large Hadron Collider (LHC) storage rings. By exciting the electronic degrees of freedom of the stored ions with lasers (i.e., primary photon beams), high energy narrow-band, fully polarized (secondary) photon beams will be produced. Their intensities, up to 1017 photons per second, will be several orders of magnitude higher than those of the presently operating light sources in the particularly interesting gammaray energy domain reaching up to 400 MeV, inaccessible with sources based on free-electron lasers. Multiple unprecedented opportunities in atomic, nuclear, particle, and applied physics may be afforded by utilizing the primary beams for spectroscopy of partially stripped ions circulating in the storage ring, as well as by the application of the secondary high-energy photon beams. The Gamma Factory provides a unique scenario of extending the use of the existing CERN accelerator infrastructure, going beyond its design goals, and allowing to open new crossdisciplinary research domains. It may enable groundbreaking