Abstract
Abstract:
The Standard Model (SM) is known to be incomplete. The introduction of a
Dark Sector via an additional U(1)D gauge symmetry added to the SM Lagrangian provides a mechanism
to introduce much needed new physics without perturbing the already excellent agreement between the
SM theoretical description and the Electroweak Precision Observables (EWPO) experimental
constraints. The model has a dark vector boson Zd which can mix with the hypercharge gauge boson
with the coupling . This opens the Hypercharge Portal which can mediate the fluctuation of a Z to a
Zd, or the decay of the Zd to SM leptons. If a dark Higgs singlet s also exists, this then breaks
the U(1)D, opening the Higgs portal and also allowing for Higgs mass mixing between the SM and dark
sectors, described by the Higgs mass mixing parameter, k. Including dark fermionic fields in the
Lagrangian allows for long-lived cold Dark Matter candidates. The various connections between the
Dark and SM sectors allow descriptions of many key astro-physical phenomena. The Model is therefore
a fascinating candidate for new physics beyond the SM. It becomes crucial to search for
experimental signatures of this model. This contribution discusses a search for the dark force
boson Zd using its production via the Higgs Portal and its decay back to SM leptons: H hd ZdZd
4l. The results from ATLAS Run
1 and the further development of the search for Run 2 are presented.