Anatomy of the ATLAS diboson anomaly

Abstract

We perform a general analysis of new physics interpretations of the recent ATLAS diboson excesses over Standard Model expectations in LHC Run I collisions. Firstly, we estimate a likelihood function for the true signal in the $WW$, $WZ$, and $ZZ$ channels, finding that the maximum has zero events in the $WZ$ channel, though the likelihood is sufficiently flat to allow other scenarios. Secondly, we survey the possible effective field theories containing the Standard Model plus a new resonance that could explain the data, finding just two possibilities, viz., a vector that is either a left- or right-handed $SU(2)$ triplet. Finally, we compare these models with other experimental data and determine the parameter regions in which they provide a consistent explanation.

8 pages, 9 figures and 5 tables. v2 has added references, corrected branching ratios for the left-handed triplet model and revised estimates of efficiencies. The cross-sections in the general likelihood analysis are significantly higher but there is no change in overall conclusion. v3 has an improved likelihood analysis using more data, conclusions unaffected. v4 is the published version