Gamma-gamma collider with cms< 12 GeV based on European XFEL

• Applicant: Professorin Dr. Gudrid Moortgat-Pick
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430227464

So far, two-photon physics has been studied at e+e– (pp) storage rings in collisions of virtual photon (γ*γ*), which make up the field of relativistic charged particles. The corresponding γ* γ* luminosity is considerably smaller than that in e+e-collisions, however, many two-photon processes have been studied. Unlike e+e– collisions, where only resonances with the photon quantum number (spin 1 and charge parity C=–1) are produced, in γγ collisions C=+1 resonances are produced with a wide set of spin and parity values.The first observation of such C=+1 resonances at e+e– colliders was done by one of the Russian authors of this project in 1979, in 1981 he put forward the idea of a real γγ (γe) collider with a high energy and luminosity based on developed high energy linear e+e– colliders, where high-energy photons are obtained by Compton scattering of laser photons on electrons near the collision point. In recent years, great progress has been made in laser technology, gamma-ray sources based on Compton scattering are being created and acceleration methods, traditional as well as advanced ones, have been further developed.Recently, the European X-ray free electron laser (XFEL) has started operation at DESY (Hamburg). It is driven by the linear superconducting electron accelerator with the energy of 17 GeV. At present, the electron beams after passing through XFEL are sent to the beam dump. We propose to redirect the beams alternately in two arches and then, just before the collison point, to convert electrons into photons using a laser with λ ~ 0.5 μm. As a result, we obtain the γγ collider with the maximum c.m.s. energy of up to 12 GeV, that overlaps the entire range of resonances, containing c- and b-quarks, where many various exotic states were found at B-factories and LHC. In addition, new light forms of matter (dark matter, light non-Standard-Model-like Higgs particles) could be accessible. High-energy photons can be made circularly or linearly polarized, which provides an unique opportunities for studying C=+1 states in this energy region, which is not possible at other colliders. The purpose of this grant is to develop in detail this proposal together with Russian colleagues. We plan to develop a physical program, calculate possible parameters of the γγ (eγ) collider, consider accelerator and laser aspects at the conceptual level that will lay the foundation for the further advancement of this project.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Professor Dr. Valery Telnov, until 3/2022