Evidence for BSM spin 0 and spin 2 resonances at LHC Possible Interpretations

TL;DR

The paper reports evidence for spin 0 and spin 2 resonances around 650 GeV at the LHC, interprets them within models like Randall-Sundrum, and discusses implications for future colliders.

Contribution

It provides a detailed interpretation of multiple resonance signals at 650 GeV, proposing a sequence of tensor and scalar resonances consistent with certain extra-dimensional models.

Findings

Observation of nine decay channels around 650 GeV.

Identification of a potential spin-2 graviton resonance T690.

Implications for future e+e- colliders based on coupling predictions.

Abstract

Nine statistically significant decay channels are observed in LHC data around a mass of 650 GeV. We interpret three of them as coming from a 20 GeV wide resonance observed in $e^+e^-$ , 2 photons and ZZ which could be a $J=2$ Kaluza Klein graviton resonance called T690 (T for tensor with J=2). This hypothesis is reinforced by noting that this signal is produced by VBF and it disappears in ZZ when treated as a scalar. Given that the six other excesses have poor mass resolution, one cannot exclude the presence of an additional wide scalar resonance called H650. Assuming a Randall Sundrum RS model, we conclude that LHC observes the predicted sequence T376, T690 and T1000. At variance with the RS model, T690 weakly couples to gluon pairs, suggesting a composite model interpretation. It does significantly couple to $e^+e^-$ which has implications for $e^+e^-$ colliders. Perturbative unitarity requirements predict $T^{++} \to W^+W^+$ and $T^+\to ZW$ resonances, again indicated by LHC data. Assuming BR($e^+e^-$ )$\sim$0.25%, deduced from ATLAS and CMS, this scenario offers excellent prospects for abundantly (Gigafactory) producing a sequence of narrow resonances at future $e^+e^-$ colliders. For heavy scalars, the situation is less clear. Following ATLAS and CMS, we expect that the top loop contribution to the gluon-gluon fusion mechanism ggF could produce a deficit rather than an excess in the mass distribution of top pairs, which prevents a standard estimate of the statistical significance for heavy resonances. It seems that the pseudo-scalar and scalar resonances A490 and H650, indicated by other channels, create observable deviations in the t t analyses presented by ATLAS and CMS. The scalar resonances seem to form the triple Higgs doublet structure predicted by Weinberg. The present note summarises these arguments and collects available indications in view of electing a future collider.