# Vector mediator, Dirac fermion DM¶

This model is one of those considered in the ATLAS search summary [14]. We have so far compared two scenarios, first one with the coupling of the mediator to quarks set to 0.25, and zero coupling to leptons (also discussed in [110]):

ATLAS Searches

Contur

(see below for important comment on the low $$M_{\rm Z^\prime}$$ region.)

Second with the mediator coupling to quarks set to 0.1, and a coupling on 0.01 to leptons.

ATLAS Searches

Contur (Rivet 2.7.x 30/4/2019)

Coupling of the mediator to quarks set to 0.25, and zero coupling to leptons

The sensitivity apparently extends to lower masses than seen in the ATLAS combined search results. However, note that the lowest mass point generated is $$M_{\rm Z^\prime}= 10$$ GeV, so the limit does not really extend to zero. Below, the $$M_{\rm Z^\prime}$$ is generated on a log scale for $$M_{\rm Z^\prime} \ge 5$$ GeV, so the low mass regime can be seen in more detail.

Coupling of the mediator to quarks set to 0.25, and zero coupling to leptons

Coupling of the mediator to quarks set to 0.1, and a coupling on 0.01 to leptons.

There is indeed sensitivity down to this value. However, it arises from marginal contributions from many analyses, principally $$\gamma +$$ jets and $$W,Z +$$ jets. Given the rather crude treatment of correlations and background in Contur at present, such a situation should be treated with caution. Nevertheless it illustrates the fact that these measurements to probe the model in that region.

In the first case the measurments in Contur have similar sensitivity to the searches, despite not having the most recent dijet data. The top measurements are especially powerful, particularly the ATLAS fully-hadronic boosted top measurement [11].

In the second case, the measurments in Contur have less sensitivity than the searches. This because there is no 13 TeV Drell-Yan measurement published yet, there is no 8 TeV dijet mass measurement, and the 13 TeV dijet data measurement only made with a few inverse fb.