Measuring the Higgs Sector

TL;DR

This paper develops and applies a comprehensive framework (SFitter) to map LHC measurements of a light Higgs sector onto a general weak-scale effective theory with a 120 GeV Higgs. By incorporating a full error treatment (statistical, systematic, and theory errors) and using exclusive likelihood mappings with cooling, it quantifies how Higgs couplings can be extracted and constrained, including correlations and potential new physics in loops or additional Higgs states. The study finds that individual Higgs couplings can be determined with roughly 20–40% accuracy at 30 fb⁻¹, that coupling ratios can offer improved precision in some cases, and that unobserved or invisible decays and beyond-the-Standard-Model scenarios (e.g., SUSY or gluophobic Higgs) leave distinctive imprints on the parameter space. Overall, the work provides a robust methodology for diagnosing the nature of the Higgs sector at the LHC and for testing deviations from the Standard Model with realistic error structures and high-dimensional parameter spaces.

Abstract

If we find a light Higgs boson at the LHC, there should be many observable channels which we can exploit to measure the relevant parameters in the Higgs sector. We use the SFitter framework to map these measurements on the parameter space of a general weak-scale effective theory with a light Higgs state of mass 120 GeV. Our analysis benefits from the parameter determination tools and the error treatment used in new--physics searches, to study individual parameters and their error bars as well as parameter correlations.

Figures (14)

• Figure 1: Profile likelihoods (left) and Bayesian probabilities (right) for the $WWH$, $ttH$, and $bbH$ couplings. Not allowing for additional $ggH$ or $\gamma\gamma H$ couplings we show results for $30~{\rm fb^{-1}}$ and for $300~{\rm fb^{-1}}$ in the upper and lower rows. The Higgs mass is chosen as 120 GeV. All experimental and theory errors are included. Here and in all other Figures we assume the $WWH$ coupling to be positive, i.e. $\Delta_{WWH}>-1$.
• Figure 2: Correlations in profile likelihoods (left) and Bayesian probabilities (right), not allowing additional effective couplings. All experimental and theory errors included for low-luminosity running.
• Figure 3: Profile likelihoods; the three rows correspond to (1) only a $ggH$ effective coupling, (2) only a $\gamma\gamma H$ effective coupling, and (3) both of them. The corresponding results without any effective coupling are shown in Fig. \ref{['fig:corr_1']}.
• Figure 4: Profile likelihoods without (left) and including (right) theory errors. The top rows assume $300~{\rm fb^{-1}}$ and no effective couplings, the bottom rows $30~{\rm fb^{-1}}$ and both effective $ggH$ and $\gamma\gamma H$ couplings.
• Figure 5: Profile likelihoods for the standard analysis (top row, copied from Fig. \ref{['fig:corr_1']}), an increased $ccH$ coupling with no additional contribution to the Higgs width (second row), an increased $ccH$ coupling and a scaling factor for the total width (third row), and finally this scaling factor only (single bottom panel). All experimental and theory errors included for low-luminosity running.