We propose a LHC search for dilepton resonances in association with large missing energy as a generic probe of TeV dark sector models. Such resonances can occur if the dark sector includes a U(1) gauge boson, or Z , which kinetically mixes with the Standard Model U(1). For small mixing, direct 2 → 1 production of the Z is not visible in standard resonance searches due to the large Drell-Yan background. However, there may be significant production of the Z boson in processes involving other dark sector particles, resulting in final states with a Z resonance and missing transverse momentum. Examples of such processes include cascade decays within the dark sector and radiation of the Z off of final state dark sector particles. Even when the rate to produce a Z boson in a dark sector process is suppressed, this channel can provide better sensitivity than traditional collider probes of dark sectors such as monojet searches. We find that data from the 8 TeV LHC run can be interpreted to give bounds on such processes; more optimized searches could extend the sensitivity and continue to probe these models in the Run II data.

Most generic models of hidden sector supersymmetry breaking do not feature singlets, and gauginos obtain masses from anomaly mediated supersymmetry breaking. If one desires a natural model, then the dominant contribution to scalar masses should be of the same order, i.e. also from AMSB. However, pure AMSB models suffer from the tachyonic slepton problem. Moreover, there is a large splitting between the gluino and the wino LSP masses resulting in tight exclusion limits from typical superpartner searches. We introduce messenger fields into this framework to obtain a hybrid theory of gauge and anomaly mediation, solving both problems simultaneously. Specifically, we find any number of vector-like messenger fields (allowed by GUT unification) compress the predicted gaugino spectrum when their masses come from the Giudice-Masiero mechanism. This more compressed spectrum is less constrained by LHC searches and allows for lighter gluinos. In addition to the model, we present gaugino pole mass equations that differ from (and correct) the original literature.

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The process e + e − → e + e − Z/γ * is studied with the OPAL detector at LEP at a centre of mass energy of √ s = 189 GeV. The cross-section times the branching ratio of the Z/γ * decaying into hadrons is measured within Lorentz invariant kinematic limits to be (1.2 ± 0.3 ± 0.1) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and (0.7 ± 0.2 ± 0.1) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variablesŝ,t, andû are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess eγ → eZ/γ * are derived.