  We show that simultaneously explaining dark matter and the observed value of
the muon's magnetic dipole moment may lead to yet unexplored photon signals at
the LHC. We consider the Minimal Supersymmetric Standard Model with
electroweakino masses in the few-to-several hundred GeV range, and opposite
sign of the Bino mass parameter with respect to both the Higgsino and Wino mass
parameters. In such region of parameter space, the spin-independent elastic
scattering cross section of a Bino-like dark matter candidate in direct
detection experiment is suppressed by cancellations between different
amplitudes, and the observed dark matter relic density can be realized via
Bino-Wino co-annihilation. Moreover, the observed value of the muon's magnetic
dipole moment can be explained by Bino and Wino loop contributions.
Interestingly, "radiative" decays of Wino-like neutralinos into the lightest
neutralino and a photon are enhanced, whereas decays into leptons are
suppressed. While these decay patterns weaken the reach of multi-lepton
searches at the LHC, the radiative decay opens a new window for probing dark
matter at the LHC through the exploration of parameter space regions beyond
those currently accessible. To complement the current electroweakino searches,
we propose searching for a single (soft) photon plus missing transverse energy,
accompanied by a hard initial state radiation jet.
