A Georgi-Machacek Interpretation of the Associate Production of a Neutral Scalar with Mass around 151 GeV

TL;DR

This paper interprets a potential 151 GeV scalar excess at the LHC within the Georgi-Machacek model, proposing a cascade decay explanation and predicting observable signals at future electron-positron colliders.

Contribution

It introduces a novel interpretation of the 151 GeV excess using the GM model, linking it to a specific cascade decay process and outlining testable predictions for future colliders.

Findings

The 151 GeV excess can be explained by the GM model's cascade decay A(400)->H(151)Z.

H(151) may decay into two light CP-odd scalars, consistent with ATLAS hints.

Predicted signals at a 1 TeV e+e- collider could confirm this scenario.

Abstract

Following an investigation of several indications for new physics from LHC data, a detailed exploration of the Georgi-Machacek (GM) model was elaborated in a previous publication. This framework is used here to interpret the findings of Crivellin et al., which were obtained by combining the 2 photon mass spectrum from ATLAS and CMS, adding extra conditions, the most efficient one being the presence of >90 GeV missing transverse energy. The claim is a ~5 s.d. excess at 151 GeV. The GM model naturally explains this as coming from the cascade A(400)->H(151)Z, where H(151) is an isosinglet predicted by GM and where the accompanying signal comes from the decay of a Z boson into neutrino pairs. Satisfying the constraints from LHC measurements of the ZWW channel, which can receive a large contribution from this cascade, suggests that H(151) could dominantly decay into two light CP-odd scalars, following an ATLAS indication for h(125) decaying into bbmumu. A spectacular occurrence of signals is predicted at an $e^+e^-$ collider operating up to 1 TeV, an energy sufficient to cover the whole scenario.