Constraints on a light leptophobic mediator from LEP data

We apply data taken at the e(+)e(-) collider LEP in the 1990's at center-of-mass energy up to 209 GeV to constrain Dark Matter models with a light leptophobic spin-1 mediator R. We assume that the dark sector particle (DSP) is a spin-1/2 fermion chi. This scenario is well studied in the context of LHC searches for mediator mass from 100 GeV to several TeV. Emission of the mediator off a quark or antiquark at LEP gives rise to di-jet plus missing energy and 4-jet signatures, which we use to limit the relevant couplings. We focus on scenarios with 2m(chi) > m(R), which are poorly constrained by LHC data. We recast published searches by the ALEPH collaboration. For m(chi) less than or similar to 20 GeV the best bounds result from an analysis at root s similar or equal to M-z of di-jet plus missing energy events. For heavier DSP but m(R) less than or similar to 70 GeV meaningful bounds can be derived from a four jet analysis at root s = 183 GeV. Unfortunately published searches using four jet final states at root s similar or equal to M-z use only a small fraction of the total data sample. Moreover, all published searches for di-jet plus missing energy final states at root s >= 130 GeV have poor efficiency for our model; we therefore design new cuts that combine good background rejection with higher efficiency. Re-analyzing the higher energy data using our new cuts, and an analysis of the complete four jet data sample taken at root s similar or equal to M-z, can explore new regions of parameter space.