- The paper presents a comprehensive global fit of Higgs signal strengths from LHC data to refine coupling measurements relative to Standard Model expectations.
- It employs combined signal strength ellipses in a two-dimensional parameter space to analyze both gluon fusion and vector boson fusion processes.
- The analysis interprets constraints on extended Higgs models, including Two-Higgs-Doublet and triplet models, to set precise bounds on new physics parameters.
Overview of the Paper: Global Fit to Higgs Signal Strengths and Couplings, and Implications for Extended Higgs Sectors
The paper presents a comprehensive analysis of the most recent data from the LHC concerning the Higgs boson, particularly focusing on refining the measurements of its production and decay channels. The authors utilize public results from ATLAS, CMS, and the Tevatron experiments to conduct a global fit of the Higgs signal strengths defined in terms of production and decay rates relative to Standard Model (SM) expectations. The objective is to provide insights into the couplings of the Higgs boson and derive constraints on new physics models where Higgs couplings may deviate from SM predictions.
Methodology and Analysis
The analysis involves the computation of combined confidence level contours for signal strengths in a 2D parameter space: (gluon fusion + ttH associated production) versus (vector boson fusion + VH associated production). This approach leverages "combined signal strength ellipses" to succinctly represent experimental data, simplifying the process of deriving constraints on extensions of the SM Higgs sector.
The paper places particular emphasis on loop-induced gluon-gluon and photon-photon couplings, invisible or undetected decays, and effective Lagrangian parametrization of Higgs couplings. These considerations are essential for exploring beyond the Standard Model (BSM) theories that might incorporate new particles or interactions affecting the Higgs sector.
Numerical Results and Constraints
- Signal Strength Ellipses: The paper provides a detailed formulation for calculating the combined likelihoods for various decay channels. Best-fit points for signal strengths are derived that correlate with each final state, such as .
- Compatibility with the Standard Model: The findings indicate that the measured Higgs couplings align well with SM predictions, thus placing stringent limits on BSM scenarios that predict substantial deviations. Numerical constraints on fermionic and vector boson couplings, loop contributions, and potential new decay paths are discussed at length.
- Parameter Fitting and Models: The fit results are applied to specific New Physics models, including Two-Higgs-Doublet models (Types I and II), the Inert Doublet Model, and the Georgi-Machacek triplet Higgs model. These fits are performed under different assumptions regarding Higgs coupling strengths and invisible decay modes. The paper reports on limits for these models, exploring parameters such as mixing angles and masses of additional Higgs states.
Theoretical and Practical Implications
The paper extensively details the methodology to derive constraints from the Higgs data, emphasizing the need for precise measurements to further explore theoretical conjectures regarding an extended Higgs sector. The analysis highlights the implications of observed signal strengths and couplings for possible New Physics, offering a framework to test models that propose additional Higgs bosons or other exotic particles.
Future Prospects
As the precision of experimental measurements continues to improve, further reduction of uncertainties in Higgs couplings is expected. This will allow for even more stringent tests of SM predictions and BSM theories. Consequently, the methods and insights presented in this paper provide crucial groundwork for future explorations and potential discoveries in the field of high-energy particle physics, especially in understanding the role of the Higgs boson within and beyond the Standard Model.