Evidence for a particle decaying to W+W- in the fully leptonic final state in a standard model Higgs boson search in pp collisions at the LHC

An update of a previous search for the standard model Higgs boson decaying to W$^+$W$^-$ in pp collisions at $\sqrt{s} = 7$ TeV and $\sqrt{s} = 8$ TeV is reported. The event sample corresponds to the full integrated luminosity collected by the CMS detector at the LHC in 2011 and 2012, corresponding to $4.9$ fb$^{-1}$ and $19.5$ fb$^{-1}$, respectively. The W$^+$W$^-$ candidates are selected in events with two oppositely charged leptons and large missing transverse momentum. An excess of events is observed above background which is consistent with the expectations from a standard model Higgs boson of mass around 125 GeV and has a statistical significance of 4.0 standard deviations for this mass. This result provides evidence for a Higgs-like particle decaying to W$^+$W$^-$. Additional standard model Higgs-like bosons are excluded in the mass range 128-600 GeV at 95\% confidence level. The hypothesis of the standard model Higgs boson for quantum numbers and couplings is tested against the hypothesis of a narrow spin-2 resonance produced through the gluon fusion mechanism and with minimal couplings to the W$^+$W$^-$ pair.