How to Measure the Spin of Dark Matter
Dark Matter has eluded us for decades and continues to do so. Currently lepton colliders provide exclusion limits on individual dark matter models, but many models may have either identical or indistinguishable signals. Hence, if more than one model is present, there is the need for new methods or observables. Using $ e^+ e^-$ processes, with a mono-photon signal and missing energy, we look into whether the polarisation of the incoming beams and the outgoing photon can be used to distinguish two dark matter models: Dark Photon and Axion-Like-Particles (ALPs). Due to the dark particles' spin and coupling structures, the two models have differing contributions and dependencies on the incoming fermions' spin. We show how the polarisation of the incoming beams can be used together with angular distributions to discriminate between the hidden photons and axion dark matter.