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 $\sqrt{s} = 8$ TeV is reported. The event sample corresponds to an integrated luminosity of $12.1 \pm 0.5$ fb$^{-1}$, collected by the CMS detector at the LHC in 2012. The 2011 results obtained at $\sqrt{s} = 7$ TeV for an integrated luminosity of $4.9$ fb$^{-1}$ are added to the present analysis. 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 125 GeV and has a statistical significance of 3.1 standard deviations for this mass. This result provides evidence for a Higgs-like particle decaying to W$^+$W$^-$. No other excess of events is observed over the full accessible mass range. Additional standard model Higgs-like bosons are excluded in the mass range 128-600 GeV at 95\% confidence level.