The production of a diphoton resonance via photon-photon fusion

Abstract

Motivated by the recent LHC observation of an excess of diphoton events around an invariant mass of 750 GeV, we discuss the possibility that this is due to the decay of a new scalar or pseudoscalar resonance dominantly produced via photon-photon fusion. We present a precise calculation of the corresponding photon-photon luminosity in the inclusive and exclusive scenarios, and demonstrate that the theoretical uncertainties associated with these are small. In the inclusive channel, we show how simple cuts on the final state may help to isolate the photon-photon induced cross section from any gluongluon or vector boson fusion induced contribution. In the exclusive case, that is where both protons remain intact after the collision, we present a precise cross section evaluation and show how this mode is sensitive to the parity of the object, as well as potential CP -violating effects. We also comment on the case of heavy-ion collisions and consider the production of new heavy colourless fermions, which may couple to such a resonance.

Measuring the Diphoton Coupling of a 750 GeV Resonance

“…In the case of the two-photon pp events, we use the Budnev flux [133], which describes properly the coupling of the photon to the proton, taking into account the proton electromagnetic structure. The survival probability of the colliding protons is expected to be close to 1 [134]; here, we implement a factor of S 2 ∼ 0.72 [135]. The exclusive production via gluon exchanges is performed following the calculations by Khoze, Martin, et al [134].…”

Digamma, what next?

“…In the left (right) panel we assume a broad (narrow) resonance. A message that can be indirectly read from figure 2 is that production from gluons or from heavy quarks remains mildly favoured with respect to production from photons [73][74][75][76][77][78][79] or light quarks, which predict a too small 13 TeV/8 TeV cross section ratio.…”

Comments on the diphoton excess: critical reappraisal of effective field theory interpretations

“…These predict higher R 13/8 ratios, R 13/8 5. In contrast, R 13/8 3(4) if S is produced through valence quark annihilation or photon fusion [19,27,[33][34][35][36] which is disfavored by more than 3 (2) σ for a narrow (wide) S. In the following we will consider these results as indicative but keep the possibility of valence quark annihilation and photon (or more generally EW vector boson) fusion dominated S production open. The results for spin-0 and spin-2 are, again, very similar.…”

“…For spin zero the cross section for events passing the VBF cuts is given by where the interference terms are negligible. For the inclusive photon fusion cross section estimate we use [36] which was obtained using the MMHTNLO pdf set [51] with NLO (in α S ) DGLAP running. The related error was estimated in [36] to be ∼ ±15 − 20%.…”