Constraining the Higgs boson width with ZZ production at the LHC

We point out that existing measurements of pp -> ZZ cross sections 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 a 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) <= 38.8 Gamma(SM)(H) approximate to 163 MeV, at the 95% confidence level. Restricting ZZ invariant masses to the M-ZZ >= 300 GeV range, we estimate that this bound can be improved to Gamma(H) <= 21 Gamma(H) (M) approximate to 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 -> 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 run II of the LHC. We estimate that such analyses can, eventually, be sensitive to a Higgs boson width as small as Gamma(H) similar to 10 Gamma(SM)(H).