Direct searches for Z′-bosons are carried out at hadron colliders, since these give access to the highest energies available.
[2] Recent classes of models have emerged that naturally provide cross section signatures that fall on the edge, or slightly below the 95% confidence level limits set by the Tevatron, and hence can produce detectable cross section signals for a Z′ boson in a mass range much closer to the Z pole-mass than the "wide width" models discussed above.
These "narrow width" models which fall into this category are those that predict a Stückelberg Z′ as well as a Z′ from a universal extra dimension (see "The Z′ hunters' guide".
On 7 April 2011, the CDF collaboration at the Tevatron reported an excess in proton–antiproton collision events that produce a W boson accompanied by two hadronic jets.
[3][4] On 2 June 2015, the ATLAS experiment at the LHC reported evidence for W′-bosons at significance 3.4 σ, still too low to claim a formal discovery.
[5] Researchers at the CMS experiment also independently reported signals that corroborate ATLAS's findings.
In March 2021, there were some reports to hint at the possible existence of Z′ bosons as an unexpected difference in how beauty quarks decay to create electrons or muons.