Bounding the Higgs Boson Width Through Interferometry

TL;DR

This paper analyzes interference between Higgs-mediated diphoton production and the gluon-fusion continuum near $m_H=125$ GeV, computing dominant NLO QCD corrections to the interference. It demonstrates that the resulting apparent mass shift of the Higgs peak depends on the Higgs width $\Gamma_H$, scales roughly as $\sqrt{\Gamma_H}$ for widths above ~30 MeV, and can be used to bound or measure $\Gamma_H$ independent of couplings. The authors show that the shift can be constrained by comparing the $\gamma\gamma$ channel to $ZZ^*$ or via the $p_T$-dependence, with HL-LHC prospects potentially achieving a bound within a factor of ~15 of the SM width. This interferometric approach provides a complementary method to direct width measurements and highlights the importance of precise NLO calculations in Higgs phenomenology.

Abstract

We study the change in the di-photon invariant mass distribution for Higgs boson decays to two photons, due to interference between the Higgs resonance in gluon fusion and the continuum background amplitude for gluon pair to photon pair. Previously, the apparent Higgs mass was found to shift by around 100 MeV in the Standard Model in the leading order approximation, which may potentially be experimentally observable. We compute the next-to-leading order QCD corrections to the apparent mass shift, which reduce it by about 40%. The apparent mass shift may provide a way to measure, or at least bound, the Higgs boson width at the Large Hadron Collider through "interferometry." We investigate how the shift depends on the Higgs width, in a model that maintains constant Higgs boson signal yields. At Higgs widths above 30 MeV the mass shift is over 200 MeV and increases with the square root of the width. The apparent mass shift could be measured by comparing with the ZZ* channel, where the shift is much smaller. It might be possible to measure the shift more accurately by exploiting its strong dependence on the Higgs transverse momentum.

Figures (5)

• Figure 1: Representative diagrams for interference between the Higgs resonance and the continuum in the diphoton channel. The dashed vertical lines separate the resonant amplitudes from the continuum ones.
• Figure 2: Diphoton invariant mass $M_{\gamma\gamma}$ distribution for pure signal (top panel) and interference term (bottom panel) after Gaussian smearing.
• Figure 3: Apparent mass shift for the SM Higgs boson versus the jet veto $p_T$.
• Figure 4: Apparent mass shift for the SM Higgs boson versus the lower cut on the Higgs transverse momentum, $p_T > p_{T,H}$.
• Figure 5: Higgs mass shift as a function of the Higgs width. The coupling $c_{g\gamma}$ has been adjusted to maintain a constant signal strength, in this case $\mu_{\gamma\gamma}=1$.