Interpreting the 750 GeV diphoton signal as technipion

TL;DR

This paper explores whether a 750 GeV diphoton excess observed at the LHC could be explained by a neutral pseudoscalar technipion within a minimal vector-like technicolor model, analyzing production mechanisms and predicting cross sections.

Contribution

It introduces a technipion interpretation for the 750 GeV diphoton signal, considering multiple production processes and estimating cross sections within a specific technicolor model.

Findings

Technipion production cross section can match observed signals with strong Yukawa coupling.

Predicted exclusive diphoton cross section at 13 TeV is about 0.2 fb.

Signal is generally below background or detection thresholds.

Abstract

We discuss whether the enhancement in the diphoton final state at $M_{\gamma \gamma}$ = 750 GeV, observed recently by the ATLAS and CMS Collaborations could be a neutral pseudoscalar technipion $\tilde{\pi}^0$. We considered two distinct minimal models for the dynamical electroweak symmetry breaking. Here we concentrate only on two-flavor vector-like technicolor model and we assume that the two-photon fusion is a dominant production mechanism. We include contributions of $2 \to 1$, $2 \to 2$ and $2 \to 3$ partonic processes. All the mechanisms give similar contributions to the cross section. With the strong Yukawa (technipion-techniquark) coupling $g_{TC} \simeq 20$ we roughly obtain the measured cross section of the "signal". With such value of $g_{TC}$ we get a relatively small total decay width $\Gamma_{\rm tot}$. We discuss also the size of the signal at lower energies (LHC, Tevatron) for $\gamma \gamma$ final states, where the enhancement was not observed. We predict a measurable cross section for neutral technipion production associated with one or two soft jets. The technipion signal is compared with the Standard Model diphoton background contributions. We observe the dominance of inelastic-inelastic $\gamma \gamma$ processes. We predict the signal cross section for purely exclusive $p p \to p p \gamma \gamma$ procesess at $\sqrt{s}$ = 13 TeV to be about 0.2 fb. Such a cross section would be, however, difficult to measure with the planned integrated luminosity. We conclude that in all considered cases the signal is below the background or/and below the threshold set by statistics although some tension can be seen.