The couplings of the Higgs boson and its CP properties from fits of the signal strengths and their ratios at the 7+8 TeV LHC

TL;DR

This paper analyzes LHC Higgs data to determine the Higgs boson's couplings and CP properties, finding it to be Standard Model-like with constraints on its CP-odd component and invisible decay width.

Contribution

It provides a comprehensive fit of Higgs couplings and CP properties using combined LHC data, employing ratios to reduce uncertainties and improve precision.

Findings

Higgs couplings are consistent with Standard Model predictions at 68% CL.

The Higgs boson is at most 68% CP-odd at 99% CL.

Invisible decay width is constrained to less than 52% of the SM width at 68% CL.

Abstract

Using the full set of the LHC Higgs data from the runs at 7 and 8 TeV center of mass energies that have been released by the ATLAS and CMS collaborations, we determine the couplings of the Higgs particle to fermions and gauge bosons as well as its parity or CP composition. We consider ratios of production cross sections times decay branching fractions in which the theoretical (and some experimental) uncertainties as well as as some ambiguities from new physics cancel out. A fit of both the signal strengths in the various search channels that have been conducted, H -> Z Z, W W, gamma gamma, tau tau and b b, and their ratios shows that the observed ~126 GeV particle has couplings to fermions and gauge bosons that are Standard Model-like already at the 68% confidence level (CL). From the signal strengths in which the theoretical uncertainty is taken to be a bias, the particle is shown to be at most 68% CP-odd at the 99%CL and the possibility that it is a pure pseudoscalar state is excluded at the 4 sigma level when including both the experimental and theoretical uncertainties. The signal strengths also measure the invisible Higgs decay width which, with the same type of uncertainty analysis, is shown to be Gamma_H^inv / Gamma_H^SM < 0.52 at the 68%CL.