Diphoton excess through dark mediators

Abstract

Preliminary ATLAS and CMS results from the first 13 TeV LHC run have encountered an intriguing excess of events in the diphoton channel around the invariant mass of 750 GeV. We investigate a possibility that the current excess is due to a heavy resonance decaying to light metastable states, which in turn give displaced decays to very highly collimated e + e − pairs. Such decays may pass the photon selection criteria, and successfully mimic the diphoton events, especially at low counts. We investigate two classes of such models, characterized by the following underlying production and decay chains: gg → S → A A → (e + e − )(e + e − ) and qq → Z → sa → (e + e − )(e + e − ), where at the first step a heavy scalar, S, or vector, Z , resonances are produced that decay to light metastable vectors, A , or (pseudo-)scalars, s and a. Setting the parameters of the models to explain the existing excess, and taking the ATLAS detector geometry into account, we marginalize over the properties of heavy resonances in order to derive the expected lifetimes and couplings of metastable light resonances. We observe that in the case of A , the suggested range of masses and mixing angles is within reach of several new-generation intensity frontier experiments.

Connection between diphoton and triboson channels in new physics searches

“…Another independent constraint comes from the full decay width of the Z boson. Value of total decay width of the Z boson is measured as Γ exp Z = 2.4952 (23) GeV [37]. It is equal to the SM theoretical prediction Γ SM Z = 2.4960 (18) GeV [38,39] within experimental uncertainties.…”

“…To illustrate this idea, we consider the specific axion-like particle model [17]. Similar models were discussed in the context of the 750 GeV resonance that would, in this case, be explained by misidentification of a pair of photons created by a relativistic axion with a single photon due to the finite granularity of the detector [17][18][19][20][21][22][23].…”

Atomki anomaly in gauged U(1)R symmetric model

“…Once produced, it decays into XX dominantly. Although the X boson itself has not been searched, its decay into an electron-positron pair could potentially be mis-reconstructed as a photon [50,51]. Diphoton events from new heavy particles have been searched at LHC and the constraints are given as < ∼ 1 fb in [52,53].…”

“…(2.6), the coupling of h 2 to top quark is suppressed by 0.12 to the SM one. Then, the signal cross section is estimated as at most 0.45 fb with converted decay probability given in [51]. Hence this constraint also can be evaded.…”

Asymmetric dark matter models and the LHC diphoton excess

“…new electroweak charged states, coupled to the EW sphalerons and new scalar states mediating the decay of these EW charged states into neutral DM particles, as in e.g [10][11][12]. Already there has been considerable work on the possible connections of the diphoton resonance to DM [3,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”