Higgs Physics at the Linear Collider

TL;DR

This work surveys how a high-luminosity $e^+e^-$ linear collider can illuminate the Higgs sector across the Standard Model and MSSM, including precision measurements of mass, total width, and couplings, as well as self-couplings, with complementary $\gamma\gamma$ and Giga-$Z$ running. It details production and decay channels, expected sensitivities, and the impact of radiative corrections on the MSSM Higgs sector, highlighting decoupling limits and regions where non-minimal Higgs states remain accessible. The analysis underscores the collider's capability to distinguish SM-like Higgs behavior from extended Higgs sectors, constrain SUSY parameters, and provide a comprehensive portrait of electroweak symmetry breaking through both direct observations and indirect precision tests. The results emphasize the synergistic value of LC measurements with Tevatron/LHC data, and show that precision Higgs physics at the LC—across mass ranges and model variants—can decisively test the mechanism responsible for generating particle masses and potentially reveal the structure of physics beyond the Standard Model.

Abstract

We review the theory of Higgs bosons, with emphasis on the Higgs scalars of the Standard Model and its non-supersymmetric and supersymmetric extensions. After surveying the expected knowledge of Higgs boson physics after the Tevatron and LHC experimental programs, we examine in detail expectations for precision Higgs measurements at a future e+e- linear collider (LC). A comprehensive phenomenological profile can be assembled from LC Higgs studies (both in e+e- and gamma-gamma collisions). The Giga-Z option can provide important constraints and consistency checks for the theory of electroweak symmetry breaking.

Figures (33)

• Figure 1: The upper Dashenhambye and the lower quiros Higgs mass bounds as a function of the energy scale $\Lambda$ at which the Standard Model breaks down, assuming $m_t=175$ GeV and $\alpha_s(m_Z)=0.118$. The shaded areas above reflect the theoretical uncertainties in the calculations of the Higgs mass bounds From Riesselmann.
• Figure 2: Branching ratios of the dominant decay modes of the Standard Model Higgs boson. These results have been obtained with the program HDECAY hdecay, and include QCD corrections beyond the leading order.
• Figure 3: Main production processes for Higgs production in $e^+e^-$ annihilation. (a) Higgsstrahlung. (b) $WW$ fusion.
• Figure 4: Cross sections for Higgsstrahlung ($e^+e^-\to Zh_{\rm SM}$) and Higgs production via $W^+W^-$ fusion ($e^+e^-\to \nu\overline{\nu} h_{\rm SM}$) and $ZZ$ fusion ($e^+e^-\to e^+e^-h_{\rm SM}$) as a function of $m_{h_{\rm SM}}$ for two center-of-mass energies, $\sqrt{s}=500$ and 800 GeV Accomando:1998wt.
• Figure 5: Cross-sections for $e^+e^-\to t\overline{t}h_{\rm SM}$ in fb for three choices of center-of-mass energy. The dashed lines correspond to the tree-level result Djouadi:1992tk, and the solid lines include the next-to-leading order QCD corrections Dittmaier:1998dz.