| Compact Muon Solenoid Experiment

Dark Higgs

Hunting the Dark Higgs

Compact Muon Solenoid Experiment

Hunting the Dark Higgs

There is considerable interest in the idea that the dark matter particle interacts with Standard Model states via the exchange of one or more new mediators, which can for example carry spin 1 (e.g. a new Z′ gauge boson) or spin 0 (e.g. an additional Higgs boson). The presence of such new mediators can lead to observable signals in a wide range of DM searches, in particular direct and indirect detection experiments and searches for missing transverse momentum at the Large Hadron Collider (LHC). These mediators could also be responsible for establishing thermal equilibrium between the visible and the dark sector in the early Universe and provide the annihilation and creation processes that set the DM relic abundance via thermal freeze-out.

Figure 1: Processes leading to missing transverse momentum signatures at the LHC. Left: a typical mono-jet process. Centre and right: processes leading to a mono-dark-Higgs signal.

Our group studies a novel signature of dark matter production at the LHC resulting from the emission of an additional Higgs boson in the dark sector. In contrast to conventional Dark Matter signatures at the LHC, where missing transverse momentum results from the recoil of Dark Matter particles against a Standard Model state from initial state radiation (see Figure 1a), here the Dark Matter particles recoil against a visibly decaying dark Higgs boson from final state radiation (figure 1b, 1c).

Figure 2: Expected sensitivity of a mono-dark-Higgs search with an integrated luminosity of 40fb−1. Dashed, dotted and dash-dotted lines correspond to ms = 50 GeV, ms = 70 GeV and ms = 90 GeV, respectively. For comparison, we show the expected sensitivity of a conventional mono-jet search and the parameter combinations for which the observed relic abundance is reproduced.

Together with theorists from DESY we explored the sensitivity to such processes as shown in Fig. 1b and 1c in a phenomenological study [1]. As an example, in Figure 2, we show the upper bound on the dark sector coupling gχ as a function of the dark Higgs mass ms for two relevant benchmark scenarios. We found out that there are ample theoretical reasons to expect the presence of an additional Higgs boson in the dark sector. If such a dark Higgs decays dominantly into SM states, it may provide us with a unique window to explore the dark sector. The only requirement is the production of any dark sector state with sufficiently large momentum, so that dark-Higgs strahlung becomes sizeable which then allows to search for the resulting visible decay products. We look forward to an implementation of this search strategy in present and upcoming runs at the LHC to explore new avenues in the hunt for DM.

We are performing a mono-dark Higgs search on 35.9 fb-1 of Run-2 data. The result is about to be published.

[1] M. Duerr, A. Grohsjean, F. Kahlhoefer, B. Penning, K. Schmidt-Hoberg and C. Schwanenberger, Hunting the dark Higgs, JHEP 1704, 143 (2017), arXiv:1701.08780 [hep-ph].