BSM Searches at a Photon Collider with Energy $E_{γγ}< 12$ GeV

Abstract

The possibility of a photon collider extension to the beam dump of the $17.5$ GeV European XFEL has already been discussed before as the first high energy collider of its sort. It would not only be the first proof of concept and test of a photon collider but would also be a collider without competition in the region of $E_{γγ}=5-12$ GeV for photon-photon collision. In this range, $b\bar{b}$ and $c\bar{c}$ resonances, tetraquarks and mesonic molecules can be observed. Furthermore, some BSM processes can also be reached in this range. In this paper we want to discuss the possibility of observing ALPs in the process of light-by-light scattering at such a collider. We will use a simplified description of the Compton backscattering process to get a first look at cross sections for the Standard Model light-by-light scattering and the extension including ALPs. Furthermore, we extend this to the full beam dynamics included prediction, discuss all effects that are important when working with a photon collider and show that the photon collider with energy $E_{γγ}<12$ GeV would offer an extended physics reach compared to current limits.

Figures (14)

• Figure 1: General scheme of a $\gamma\gamma$, $\gamma e$ collider Telnov_2020.
• Figure 2: Energy spectrum for backscattered photons for different values of $x$ (left plot) and different combinations of initial electron and photon polarisation with $x=4.8$ (right plot).
• Figure 3: Luminosity spectra for a photon collider at different values of $x$ (left plot), corresponding to different energies of the $e$-beam and laser (eq. (\ref{['eq:x']})), and for various distances $b$ between the $C$ and $IP$ (right plot), defined by the parameter $\rho^2$ (eq. (\ref{['eq:rho']})). Both electron beams and lasers are unpolarised $\lambda_e=P_c=0$.
• Figure 4: Luminosity spectrum for different choices of incoming electron and laser photon polarisations (left) and the contribution of the $J_z=0,2$ states for different values of $\rho$ (right). The solid lines are for $\rho^2=0$, the dashed for $\rho^2=1$ and the dotted-dashed for $\rho^2=4$.
• Figure 5: Mean helicity of Compton scattered photons with $x=0.65$ (left) and $x=4.8$ (right) for different initial laser photon polarisations $P_c$ and electron helicity $\lambda_e$.