The apparent excess in the Higgs to di-photon rate at the LHC: New Physics or QCD uncertainties?

TL;DR

The paper investigates whether the observed excess in Higgs to diphoton decay rate at the LHC can be explained by standard QCD uncertainties rather than new physics, emphasizing the importance of accounting for theoretical uncertainties.

Contribution

It demonstrates how incorporating QCD uncertainties into Higgs production cross section calculations reduces the apparent excess in the diphoton channel to within one standard deviation.

Findings

QCD uncertainties significantly affect Higgs production rate predictions.

Accounting for these uncertainties reduces the excess to about one standard deviation.

Standard QCD effects may explain the observed diphoton rate without new physics.

Abstract

The Higgs boson with a mass $M_H \approx 126$ GeV has been observed by the ATLAS and CMS experiments at the LHC and a total significance of about five standard deviations has been reported by both collaborations when the channels $H\to \gamma \gamma$ and $H\to ZZ \to 4\ell$ are combined. Nevertheless, while the rates in the later search channel appear to be in accord with those predicted in the Standard Model, there seems to be an excess of data in the case of the $H\to \gamma\gamma$ discovery channel. Before invoking new physics contributions to explain this excess in the di--photon Higgs rate, one should verify that standard QCD effects cannot account for it. We describe how the theoretical uncertainties in the Higgs boson cross section for the main production process at the LHC, $gg \to H$, which are known to be large, should be incorporated in practice. We further show that the discrepancy between the theoretical prediction and the measured value of the $gg \to H \to \gamma \gamma$ rate, reduces to about one standard deviation when the QCD uncertainties are taken into account.