BSM searches at a photon collider with energy Eγγ < 12 GeV

A bstract The possibility of implementing a photon collider extension to the beam dump of the 17 . 5 GeV European XFEL has already been discussed in the literature as the first high energy collider of its sort. It would not only be the first proof of concept of a photon collider but would also be a unique collider in the region of E γγ = 5 − 12 GeV for photon-photon collision. In this range, bb̄ b b ¯ and cc̄ c c ¯ resonances, tetraquarks and mesonic molecules can be observed. Furthermore, several Beyond Standard Model (BSM) scenarios are also accessible in this range. In this paper we discuss the possibility of observing ALPs in the process of light-by-light scattering at such a collider. We use a simplified description of the Compton backscattering process to derive cross-sections for light-by-light scattering in the Standard Model and its extension via axion-like particles, the ALPs. Furthermore, we include the complete beam dynamics in the prediction and discuss all relevant effects that are important when working at a photon collider. We show that the photon collider with an energy of E γγ < 12 GeV offers a valuable extended physics reach compared to current ALPs limits.