APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Neil Barrie (Sydney Univ.) Explaining the LHC 750 GeV Diphoton Excess via Photon Fusion Thu, May 26, 2016, 13:30 - 14:30 Seminar Room A 1703.pdf The ATLAS and CMS Collaborations recently reported excesses of two-photon events in 13 TeV proton-proton collisions at the LHC. The reported excess appears only in the diphoton channel, without accompanying leptons, jets or any significant missing energy. This implies a relatively large coupling of the resonance to photons, which may hint that the putative resonance is produced predominantly via photon fusion. Motivated by this, we propose two possible models to explain the production of this 750 GeV resonance via photon fusion. Firstly, we consider the resonance to be a heavy composite axion that results from the condensation of a hypothetical quark in a high-colour representation of conventional QCD. This model, motivated by a recently proposed solution to the strong CP problem, is very economical and is essentially defined by the properties of the additional quark. Secondly, we consider a hypothetical heavy leptonium, the scalar bound state of an exotic lepton-antilepton pair. The constituent vector-like and weak isospin singlet leptons are assumed to carry a large hypercharge, $Y_{\ell}$, which is the only free parameter in the minimal scenario. In addition to the 750 GeV resonance, we predict the existence of a spin-1 ortho-leptonium bound state.