Measurement of the properties of the 125 GeV Higgs boson with the CMS detector

The measurement of the properties of the recently discovered boson is central to the LHC physics program. In this contribution we review preliminary measurements of the properties of the new 125 GeV boson performed by the CMS experiment using the full proton-proton dataset collected in 2011–12 (~25 fb⁻¹). In the H → ZZ (4l) channel, a signal significance of 6.7σ is now observed. In the other high-resolution mode, H → γγ, updated results were obtained on the signal strength, μ = σ/σ_SM, which is now measured to be ~0.8 ± 0.3. The two high-resolution modes allowed independent determinations of the Higgs mass: 125.8±0.6 GeV, in H → ZZ (4l); and 125.4±0.8 GeV, in H → γγ. The four-lepton channel permitted tests of the spin-parity of the new boson. From these studies, the pure pseudoscalar hypothesis is excluded at 99.8% C.L. and, for the first time, simple spin 2 models are excluded with greater than 98.5% C.L. Significantly, strong evidence is seen in a fermionic decay mode of the Higgs for the first time, namely in the H → ττ channel, which is reported with a significance of nearly 3σ. The new measurements of the spin-parity (J^P) assignments for this particle, coupled with the measured strength of the interaction of this particle with other particles, strongly indicates that the new particle is a Higgs boson, responsible for the Electroweak Symmetry Breaking. While all of these measurements are consistent with values predicted for a SM Higgs boson, they still fall far short of the requisite precision to rule out all BSM scenarios. Additional data from Run 2 of the LHC and HL-LHC will be needed to firmly establish this conclusion.