Can the diphoton enhancement at 750 GeV be due to a neutral technipion?

TL;DR

This paper explores whether a 750 GeV diphoton excess observed at LHC can be explained by a neutral technipion within two minimal technicolor models, analyzing production mechanisms, cross sections, and experimental consistency.

Contribution

It introduces two minimal technicolor models for the 750 GeV diphoton excess and evaluates their production mechanisms and experimental signatures.

Findings

Technipion production via photon fusion and gluon fusion can account for the observed cross section.

Predicted cross sections are small, around 0.2 fb for exclusive processes at 13 TeV.

Signal is generally below background and challenging to detect with planned luminosities.

Abstract

We discuss a scenario in which the diphoton enhancement at $M_{\gamma \gamma}$ = 750 GeV, observed by the ATLAS and CMS Collaborations, is a neutral technipion $\tilde{\pi}^0$. We consider two distinct minimal models for the dynamical electroweak symmetry breaking. In a first one, two-flavor vector-like technicolor (VTC) model, we assume that the two-photon fusion is a dominant production mechanism. We include $\gamma \gamma \to {\tilde \pi}^0$ and production of technipion associated with one or two jets. All the considered mechanisms give similar contributions. With the strong Yukawa (technipion-techniquark) coupling $g_{TC}$ = 10 - 20 we obtain the measured cross section of the "signal". With such values of $g_{TC}$ we get a relatively small $\Gamma_{\rm tot}$. In a second approach, one-family walking technicolor (WTC) model, the isoscalar technipion is produced dominantly via the gluon-gluon fusion. We also discuss the size of the signal at lower energies (LHC, Tevatron) for $\gamma \gamma$ (VTC) and jet-jet (WTC) final states and check consistency with the existing experimental data. We predict a measurable cross section for ${\tilde \pi}^0$ production associated with one or two soft jets. The technipion signal in both models is compared with the SM background diphoton contributions. We observe the dominance of inelastic-inelastic processes for $\gamma \gamma$ induced processes. In the VTC scenario, we predict the signal cross section for purely exclusive $p p \to p p \gamma \gamma$ processes 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. In all considered cases the signal is below the background or/and below the threshold set by statistics.