Abstract
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 χ. 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 2mχ > mR, which are poorly constrained by LHC data. We recast published searches by the ALEPH collaboration. For mχ ≲ 20 GeV the best bounds result from an analysis at sqrt{s} ≃ MZ of di-jet plus missing energy events. For heavier DSP but mR ≲ 70 GeV meaningful bounds can be derived from a four jet analysis at sqrt{s}=183 GeV. Unfortunately published searches using four jet final states at sqrt{s} ≃ MZ use only a small fraction of the total data sample. Moreover, all published searches for di-jet plus missing energy final states at sqrt{s}ge 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 sqrt{s} ≃ MZ, can explore new regions of parameter space.
Highlights
20 GeV the best bounds result from an analysis at s MZ of di-jet plus missing energy events
We apply data taken at the e+e− collider Large Electron Positron 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
For pure axial vector coupling the upper bound on the coupling we derive from our recasting of the LEP1 data saturates the unitarity constraint at mχ 23 GeV, with larger mR yielding a slightly larger range of mχ where the experimental bound is below the unitarity limit
Summary
We first describe the Lagrangian of the simplified model we consider. We discuss limits on the model parameters that follow if the DSP is assumed to be a thermal WIMP, which is subject to stringent constraints from direct dark matter search experiments. In the following two subsections we discuss upper bounds on the couplings that result from perturbativity and unitarity constraints. In the final subsection the precollider bounds on the remaining free parameters are summarized and our final choice of free parameters is discussed
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