Abstract
We study kinematic distributions that may help characterise the recently observed excess in diphoton events at 750 GeV at the LHC Run 2. Several scenarios are considered, including spin-0 and spin-2 750 GeV resonances that decay directly into photon pairs as well as heavier parent resonances that undergo three-body or cascade decays. We find that combinations of the distributions of the diphoton system and the leading photon can distinguish the topology and mass spectra of the different scenarios, while patterns of QCD radiation can help differentiate the production mechanisms. Moreover, missing energy is a powerful discriminator for the heavy parent scenarios if they involve (effectively) invisible particles. While our study concentrates on the current excess at 750 GeV, the analysis is general and can also be useful for characterising other potential diphoton signals in the future.
Highlights
JHEP05(2016)128 of specific final states vary between different concrete models
We find that combinations of the distributions of the diphoton system and the leading photon can distinguish the topology and mass spectra of the different scenarios, while patterns of QCD radiation can help differentiate the production mechanisms
An analogous behaviour is observed for the second photon, where for a narrow width, the pT (γ2) distribution has a sharp cut-off near mX0/2 = 375 GeV, while for a broad width there is a larger tail towards higher pT values
Summary
As briefly discussed in the Introduction, the various scenarios for the diphoton excess can be quite generically classified according to the number and the nature of the final state particles as well as according to the initial state producing them in the first place. The Landau-Yang theorem [52, 53] guarantees that Xs can be a spin-0 particle X0 or a spin-2 particle X2 In either case it can be produced via gluon, qq, photon or vector boson fusion, or in association with a vector boson or a pair of top quarks. Out of these cases, we consider gg and bb production of a spin-0 resonance, and gg and qqproduction of a spin-2 one, as depicted in figure 1. Corresponding to the gluon-dominant, universal coupling, and quark-dominant scenarios, respectively These scenarios amount to 99%, 87% and 7% gluon fusion contributions to the total 750 GeV spin-2 resonance production cross section at the 13 TeV LHC respectively [44]
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