Can the 126 GeV boson be a pseudoscalar?

Abstract

We test the possibility that the newly-discovered 126 GeV boson is a pseudoscalar by examining the correlations among the loop-induced pseudoscalar decay branching fractions to $\gamma \gamma$, $Z{Z}^{\ast }$, $Z\gamma$, and $W{W}^{\ast }$ final states in a model-independent way. These four decays are controlled by only two effective operators, so that the rates in $Z\gamma$ and $W{W}^{\ast }$ are predicted now that the rates in $\gamma \gamma$ and $Z{Z}^{\ast },Z{\gamma }^{\ast }\to 4\ell$ have been measured. We find that the pseudoscalar possibility is disfavored but not conclusively excluded. Experimental exclusion of the $Z\gamma$ decay to well below $\sigma /{\sigma }_{\mathrm{SM}}\sim 170$ or conclusive observation of the $W{W}^{\ast }$ decay near the Standard Model rate would eliminate the pseudoscalar possibility. The $Z\gamma$ exclusion should be possible using existing data. The only loophole in our argument is the possibility that the $4\ell$ signal comes from pseudoscalar decays to a pair of new neutral gauge bosons with mass near the $Z$ pole.

8 pages, 2 figures, v2: references added, Fig. 1 improved,v3: minor error in numbers on last paragraph of pg5 fixed

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• Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
• Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC
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