The Search for the dark vector boson

by Diallo Boye

Wednesday 10 Apr 2019, 16:00 → 17:00 US/Eastern

Hidden sector or dark sector states appear in many extensions to the Standard
Model, to provide a particulate candidate for dark matter in universe or to explain
astrophysical observations such the as positron excess observed in the cosmic radiation
flux. A hidden or dark sector can be introduced with an additional U(1)d dark gauge
symmetry. The presence of the dark sector could be experimentally inferred at colliders
as deviations from the SM-predicted rates of Drell-Yan (DY) events, from Higgs boson
decays through exotic intermediate states, or other processes which may depart from the
SM predictions. The discovery of the Higgs boson during Run 1 of the Large Hadron
Collider opens a new and rich experimental program based on the Higgs Portal. This
discovery route uses couplings to the dark sector at the Higgs level, which were not
experimentally accessible before. These searches de the study of possible exotic decays:
H -> Z Zd -> 4l and H -> Zd Zd ->4l. Here Zd is a dark vector boson. We have experience
of this search from the Run 1 period of the LHC using the ATLAS detector at CERN.
These results showed (tantalizingly) two signal events where none were expected, so that
in the strict criteria of High Energy Physics, the result was not yet statistically significant.
The Run 1 analysis for 8 TeV collision energy is further developed in Run 2 with 13 TeV
collision energy, to expand the search area, take advantage of higher statistics, a higher
Higgs production cross section, and substantially better performance of the ATLAS
detector. As things evolved, the search now further broadened and includes allowing the
mass of the originating boson (the dark Higgs) to vary away from the SM value. This
allows the search for the dark vector boson to also explore higher masses (instead of
limiting the dark boson to 60 GeV as Run1 and Run2). This extended search is efficient
and could include a more general class of models, with the constraint of the SM Higgs
portal lifted. This contribution reviews the results for Run1 and Run2 and also presents
the extension of this analysis to the heavy scalar case.