科研之友
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摘要
We discuss the diboson excess seen by the ATLAS collaboration around 2TeV in the LHC run I at root s = 8TeV. We explore the possibility that such an excess can arise from a Z' boson which acquires mass through a U(1)(X) Stueckelberg extension. The corresponding Z' gauge boson is leptophobic with a mass of around 2TeV and has interactions with SU(2)(L) Yang-Mills fields and gauge fields of the hypercharge. The analysis predicts Z' decays into WW and ZZ as well as into Z gamma. Further three-body as well as four-body decays of the Z' such as WWZ, WW gamma, WWZZ etc are predicted. In the analysis we use the helicity formalism which allows us to exhibit the helicity structure of the Z' decay processes in an transparent manner. In particular, we are able to show the set of vanishing helicity amplitudes in the decay of the massive Z' into two vector bosons due to angular momentum conservation with a special choice of the reference momenta. The residual set of non-vanishing helicity amplitudes are identified. The parameter space of the model compatible with the diboson excess seen by the ATLAS experiment at root s = 8TeV is exhibited. Estimate of the diboson excess expected at root s = 13TeV with 20 fb(-1) of integrated luminosity at LHC run II is also given. It is shown that the WW, ZZ and Z gamma modes are predicted to be in the approximate ratio 1 : cos(2) theta(W) (1+ alpha tan(2) theta(W))(2)/2 : (1 - alpha)(2) sin(2) theta(W) = 2 where alpha is the strength of the coupling of Z' with the hypercharge gauge field relative to the coupling with the Yang-Mills gauge fields. Thus observation of the Z gamma mode as well as three-body and four-body decay modes of the Z' will provide a de finite test of the model and of a possible new source of interaction beyond the standard model.
