Z' Bosons from E(6): Collider and Electroweak Constraints
  Many models beyond the Standard Electroweak Theory, top-down or bottom-up, contain extensions of the gauge symmetry group by extra U(1)' factors which can be understood or treated as subgroups of E(6). A brief overview of such models is followed by a sketch of a systematic classification. We then describe how the resulting extra massive neutral gauge bosons can be searched for and in case of positive evidence diagnosed using electroweak and collider data. 
Jens Erler, Paul Langacker, Shoaib Munir and Eduardo Rojas
hep-ph hep-ex