Search for Dark Photons from Supersymmetric Hidden Valleys

We search for a new light gauge boson, a dark photon, with the D0 experiment. In the model we consider, supersymmetric partners are pair produced and cascade to the lightest neutralinos that can decay into the hidden sector state plus either a photon or a dark photon. The dark photon decays through its mixing with a photon into fermion pairs. We therefore investigate a previously unexplored final state that contains a photon, two spatially close leptons, and large missing transverse energy. We do not observe any evidence for dark photons and set a limit on their production.

Figure 1

One of the diagrams giving rise to the events with a photon, dark photon (${\gamma }_D$), and large missing energy due to escaping dark neutralinos ($\tilde{X}$) at the Fermilab Tevatron Collider.

Figure 2

Observed mass distributions in the signal region are represented as points with error bars, the background estimation is shown as filled band, and an example signal for $m_{{\gamma }_D}=1.4\mathrm{GeV}$ plus background is shown as the solid histogram for the dimuon channel (a) and the dielectron channel (b).

Figure 3

The excluded region of possible masses of the lightest chargino and the dark photon for $\mathcal{B}=0.5$ are shown as the shaded region. The expected limit is illustrated as the dash-dotted line. The vertical black line corresponds to the exclusion from the diphoton search [21].

Figure 4

The dependence of the excluded chargino masses on the branching ratio of the neutralino into a photon are given for dark photon masses of 0.2, 0.782, and 1.5 GeV. The black contour corresponds to the exclusion from the diphoton search [21].