Abstract
Inelastic dark matter is an interesting scenario for light thermal dark matter which is fully consistent with all cosmological probes as well as direct and indirect dark matter detection. The required mass splitting between dark matter χ1 and its heavier twin χ2 is naturally induced by a dark Higgs field which also provides a simple mechanism to give mass to the dark photon A′ present in the setup. The corresponding dark Higgs boson h′ is naturally the lightest dark sector state and therefore decays into Standard Model particles via Higgs mixing. In this work we study signatures with displaced vertices and missing momentum at Belle II, arising from dark Higgs particles produced in association with dark matter. We find that Belle II can be very sensitive to this scenario, in particular if a displaced vertex trigger is available in the near future.
Highlights
Apply but are relevant only for masses mχ1 10 MeV [27]
We point out that some regions of parameter space will not be covered with the current experimental configuration and that a displaced vertex trigger would be highly beneficial to increase the sensitivity to this scenario
We show 90% C.L. limits for all signatures analysed in this work, i.e. for the monophoton as well as the two displaced signatures at Belle II
Summary
A stable Majorana fermion χ1 that can be excited to a state χ2 by absorbing a massive dark photon, Aμ, is usually called inelastic DM. Note that we are working in the unitary gauge and correspondingly we do not write the Goldstone mode associated with φ In terms of these fields, the Lagrangian in eq (2.1) reads with. Together with additional terms from the covariant derivatives of the scalar Lagrangian that give mass to the gauge bosons. This is the (dark) Higgs mechanism, which demands that the cubic interaction between one scalar and two gauge bosons must be proportional to the corresponding mass. Since they are crucial for our work, we write them explicitly. Overall the model contains two independent portals between the dark and visible sector, leading to a ‘two mediator’ model with a rather complex phenomenology (see e.g. [38, 39] for a recent discussion)
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