Higgs Precision (Higgcision) Era begins

TL;DR

The paper develops a model-independent framework to quantify deviations of Higgs couplings from SM predictions, encompassing scalar and pseudoscalar Yukawas, HVV interactions, and loop-induced Hγγ and Hgg processes through parameters like C_u^S, C_v, ΔS^γ, ΔS^g, and ΔΓ_tot. It performs global fits to Higgs data from ATLAS, CMS, and Tevatron, examining both CP-conserving and CP-violating scenarios, and compares results before and after the Moriond 2013 updates, notably the CMS diphoton shift. The main findings are that the SM Higgs provides a good fit to the post-Moriond data, with the total nonstandard width constrained to ΔΓ_tot ≲ 1.2 MeV (≈22% nonstandard branching) at 95% CL, while nonzero CP-odd components are not excluded but do not improve fits. The analysis illustrates how contributions to loop-induced vertices (ΔS^γ, ΔS^g) dominated pre-Moriond can be supplanted by SM-consistent Yukawa/ HVV patterns after Moriond, marking a transition to a true Higgs-precision era, or Higgcision, in which increasingly precise measurements will further refine or challenge the SM couplings.

Abstract

After the discovery of the Higgs boson at the LHC, it is natural to start the research program on the precision study of the Higgs-boson couplings to various standard model (SM) particles. We provide a generic framework for the deviations of the couplings from their SM values by introducing a number of parameters. We show that a large number of models beyond the SM can be covered, including two-Higgs-doublet models, supersymmetric models, little-Higgs models, extended Higgs sectors with singlets, and fourth generation models. We perform global fits to the most updated data from CMS, ATLAS, and Tevatron under various initial conditions of the parameter set. In particular, we have made explicit comparisons between the fitting results BEFORE and AFTER the Moriond 2013 meetings. Highlights of the results include: (i) the nonstandard decay branching ratio of the Higgs boson is less than 22%; (ii) the most efficient way to achieve the best fit for the data before the Moriond update is to introduce additional particle contributions to the triangular-loop functions of Hγγand Hgg vertices; (iii) the 1σallowed range of the relative coupling of HVV is 1.01 +0.13 -0.14, which means that the electroweak-symmetry breaking contribution from the observed Higgs boson leaves only a small room for other Higgs bosons; (iv) the current data do not rule out pseudoscalar couplings nor pseudoscalar contributions to the Hγγand Hgg vertices; and (v) the SM Higgs boson provides the best fit to all the current Higgs data.

Figures (11)

• Figure 1: The confidence-level regions of the fit by varying $\Delta S^\gamma$ and $\Delta S^g$ only, (a) in the $(\Delta S^\gamma,\Delta S^g)$ plane and (b) in the corresponding $(C_\gamma, C_g)$ plane. The contour regions shown are for $\Delta \chi^2 \le 2.3$ (red), $5.99$ (green), and $11.83$ (blue) above the minimum, which correspond to confidence levels of $68.3\%$, $95\%$, and $99.7\%$, respectively. The best-fit point is denoted by the triangle.
• Figure 2: The confidence-level regions of the fit by varying $\Delta S^\gamma$, $\Delta S^g$, and $\Delta \Gamma_{\rm tot}$, (a) in the $(\Delta S^\gamma,\Delta \Gamma_{\rm tot})$ plane, (b) in the $(\Delta S^g,\Delta \Gamma_{\rm tot})$ plane, (c) in the $(\Delta S^\gamma,\Delta S^g)$ plane, (d) in the corresponding $( C_\gamma , C_g)$ plane. The description of contour regions is the same as Fig. \ref{['case1']}.
• Figure 3: The confidence-level regions of the fit by varying $C_u^S$, $C_d^S$, $C_\ell^S$ and $C_v$ while keeping $\Delta S^\gamma = \Delta S^g =\Delta \Gamma_{\rm tot} =0$. The description of contour regions is the same as Fig. \ref{['case1']}.
• Figure 4: (a) Same as Fig. \ref{['case2-1']} but in the corresponding plane of $(C_\gamma, C_{g})$. (b) Prediction in the corresponding $(C_\gamma, C_{Z\gamma})$ plane. The description of contour regions is the same as Fig. \ref{['case1']}.
• Figure 5: The confidence-level regions of the fit by varying $C_u^S$, $C_d^S$, $C_\ell^S$, $C_v$, $\Delta S^\gamma$ and $\Delta S^g$ while keeping $\Delta \Gamma_{\rm tot} =0$. Shown are the correlations among ($C_u^S$, $C_d^S$, $C_\ell^S$, $C_v$). The description of contour regions is the same as Fig. \ref{['case1']}.