First interpretation of the 750 GeV diphoton resonance at the LHC

We scrutinize the evidences recently reported by the ATLAS and CMS collaborations for compatible 750 GeV resonances which appear in the diphoton channels of the two experiments in both the 8 and 13 TeV data sets. Similar resonances in diboson, dilepton, dijet, and $t\overline{t}$ final states are instead not detected. After discussing the properties and the compatibility of the reported signals, we study the implications on the physics beyond the Standard Model with particular emphasis on possible scalar extensions of the theory such as singlet extensions and the two Higgs doublet models. We also analyze the significance of the new experimental indications within the frameworks of the minimal supersymmetric standard model and of technicolor models. Our results show that a simple effective singlet extension of the SM achieves phenomenological viability with a minimal number of free parameters. The minimal supersymmetric model and the two Higgs doublet model, on the other hand, cannot explain the 750 GeV diphoton excess. Compatibility with the observed signal requires the extension of the particle content of these models, for instance by heavy vector quarks in the case of the two Higgs doublet model.

Figure 1

The production cross section times branching ratios of electroweak gauge bosons for an on-shell 750 GeV pseudoscalar or scalar mediator as a function of the parameter $b$ of Eq. (7).

Figure 2

68%, 95%, and 99% C.L. contour plots in $1/\tan \beta$ and $\cos (\beta -\alpha )$ plane for all 2HDMs, with the shaded region excluded by the $t\overline{t}$ experimental constraint [7]. In each plot, the red star represents the point of minimum for ${\chi }^2$.

Figure 3

68%, 95%, and 99% C.L. contour plots in $1/\tan \beta$ and $\cos (\beta -\alpha )$ plane for the MSSM with $R_t=0.9(1.1)$, left (right) panel, with the shaded region excluded by the $t\overline{t}$ experimental constraint [7]. In each plot, the red star represents the point of minimum for ${\chi }^2$.