Shift in the LHC Higgs diphoton mass peak from interference with background

Abstract

The Higgs diphoton amplitude from gluon fusion at the LHC interferes with the continuum background induced by quark loops. I investigate the effect of this interference on the position of the diphoton invariant mass peak used to help determine the Higgs mass. At leading order, the interference shifts the peak towards lower mass by an amount of order 150 MeV or more, with the precise value dependent on the methods used to analyze and fit the data.

Figures (6)

• Figure 1: The distribution of diphoton invariant masses from the real interference term in eq. (\ref{['eq:NintR']}), as a function of $M_{\gamma\gamma} = \sqrt{\hat{s}}$, from eq. (\ref{['eq:sigmahint']}), before including experimental resolution effects. The right panel is a close-up of the left panel, showing the maximum and minimum near $M_{\gamma\gamma} = M_H \pm \Gamma_H/2$.
• Figure 2: The distribution of diphoton invariant masses from the real interference, as in Figure \ref{['fig:unsmeared']}, but now smeared by various Gaussian mass resolutions with widths $\sigma_{\rm MR}$.
• Figure 3: Diphoton invariant mass distributions with a Gaussian mass resolution of width $\sigma_{\rm MR} = 1.7$ GeV. In each panel, the right (red) curve includes only the Higgs contribution without interference, and the left (blue) curve also includes the interference contribution from Figure \ref{['fig:diffsmeared']}. The right panel is a close-up of the left panel.
• Figure 4: The shift in the diphoton invariant mass distribution due to interference with the continuum background, using the measure of eqs. (\ref{['eq:defNdelta']})-(\ref{['eq:defDeltaM']}), for various assumed values of the mass resolution Gaussian width $\sigma_{\rm MR}$.
• Figure 5: Angular distributions for the diphoton Higgs signal-background interference. In the left panel, the shape of the interference contribution $(1/\sigma_{\rm int})d\sigma_{\rm int}/d(|\cos\theta_{\rm CM}|)$, where $\theta_{\rm CM}$ is the diphoton center-of-mass scattering angle. In the right panel, the ratio of the acceptances $R = (\sigma_{\rm cut}^{\rm int}/\sigma^{\rm int}_{\rm total})/ (\sigma^{H}_{\rm cut}/\sigma^{H}_{\rm total})$, where "int" refers to the Higgs-continuum interference part from eq. (\ref{['eq:NintR']}) and "$H$" to the Higgs contribution without interference from eq. (\ref{['eq:NH']}), and "cut" means $|\eta| < \eta_{\rm max}$ for both photons, while "total" means no cut on $\eta$.