Dark Sector
There is substantial evidence of the existence of dark matter from gravitational and cosmological measurements, but the lack of solid evidence for dark matter particles from direct dark matter searches has forced us to rethink the main paradigms used to describe what dark matter can be. In recent years, the SUSY candidates (like the supersymmetric particle called neutralino) that were at the centre of the so-called WIMP (weakly interacting massive particles) miracle have not been discovered (and very likely never will), suggesting the need to provide new alternative models that could account for dark matter.
Enter the dark sector or dark sectors. A new hypothetical set of new particles and interactions that might provide a viable candidate to dark matter and that are often proposed in a mass range of up to a few GeV, and therefore of interest for Belle II.
I have coordinated several searches [see here, here, or here for example] for dark sector particles at the Belle II experiment. The search for invisible decays of hypothetical, light, Z' boson has been a central focus of my research for some time, but I have also searched for muonic decays of this boson, or even the associated production of an invisible Dark Higgs boson and a dark photon decaying to muons. Unfortunately, no new particle has been discovered in these searches, but we could exclude a wide range of parameters that these particles could have (for example, their masses and coupling constants).
The figures below show how the production and invisible decay of a light Z' boson might look at the Belle II experiment and the results of one of the most recent searches we performed at Belle II.
New searches are ongoing, and even if no new particles are discovered, they impact science. First, a negative outcome allows us to constrain or exclude models that predict the existence of these particles. Second, to search for evidence of these particles, we must look at noisy data, and developing and exploiting the most advanced analysis techniques is a must with potential that goes beyond the scope of each individual search.
One of my phenomenology works, where the relation between the searches for Z' bosons and other flavour observables was investigated, can be found here.