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

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 into four leptons which could be a J=2 Kaluza Klein graviton resonance called T700 (T for tensor with J=2). This hypothesis is reinforced by noting that this signal is produced by VBF and not by ggF since 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 T380, T700 and T1000, with prospects to discover heavier states by reconstructing hadronic states. At variance with the RS model, T700 decouples from gluon and photon pairs, suggesting a composite model interpretation in which preons are charge neutral and colourless. T700 does significantly couple to $e^+e^-$ which has implications for future $e^+e^-$ colliders. Perturbative unitarity requirements predict $T^{++} \to W^+W^+$ and $T^+ \to ZW$ resonances, again indicated by LHC data. With BR($e^+e^-$)~0.25%, measured by 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 $t \bar t$ analyses presented by ATLAS and CMS.