Constraining the Higgs boson width with ZZ production at the LHC

TL;DR

This paper demonstrates a model-independent method to constrain the Higgs boson width using off-shell ZZ production data from the LHC, providing bounds that improve with higher invariant mass ranges.

Contribution

It introduces a novel approach to bound the Higgs width using existing ZZ production measurements, applicable across a broad mass range, and translates these bounds into limits on invisible decay branching ratios.

Findings

Upper bound on Higgs width: 38.8 times SM value from CMS data.

Stronger bound: 21 times SM width for ZZ masses above 300 GeV.

Potential to reach sensitivity to widths as small as 10 times SM value.

Abstract

We point out that existing measurements of $pp \to ZZ$ cross-section at the LHC in a broad range of ZZ invariant masses allow one to derive a model-independent upper bound on the Higgs boson width, thanks to strongly enhanced off-shell Higgs contribution. Using CMS data and considering events in the interval of ZZ invariant masses from 100 to 800 GeV, we find $\Gamma_H \le 38.8 \times \Gamma_H^{SM} \approx 163$ MeV, at the $95\%$ confidence level. Restricting ZZ invariant masses to $M_{ZZ} \ge 300$ GeV range, we estimate that this bound can be improved to $\Gamma_H \le 21 \times \Gamma_H^{SM} \approx 88$ MeV. Under the assumption that all couplings of the Higgs boson to Standard Model particles scale in a universal way, our result can be translated into an upper limit on the branching fraction of the Higgs boson decay to invisible final states. We obtain $Br(H \to inv) < 0.84 (0.78)$, depending on the range of ZZ invariant masses that are used to constrain the width. We believe that an analysis along these lines should be performed by experimental collaborations in the near future and also in the run II of the LHC. We estimate that such analyses can, eventually, be sensitive to the Higgs boson width as small as $\Gamma_H \sim 10 \times \Gamma_H^{SM}$.