[Paper Review] The Anatomy of Electro-Weak Symmetry Breaking. I: The Higgs boson in the Standard Model

A. Djouadi|arXiv (Cornell University)|Mar 17, 2005

Particle physics theoretical and experimental studies540 citations

TL;DR

This comprehensive review details the Higgs boson's properties, decay modes, and production mechanisms within the Standard Model, focusing on precision calculations for LHC and future lepton colliders. It presents detailed cross-section predictions, radiative corrections, and strategies for measuring the Higgs boson's spin and CP quantum numbers using angular distributions and beam polarization at e+e− and muon colliders.

ABSTRACT

This review is devoted to the study of the mechanism of electroweak symmetry breaking and this first part focuses on the Higgs particle of the Standard Model. The fundamental properties of the Higgs boson are reviewed and its decay modes and production mechanisms at hadron colliders and at future lepton colliders are described in detail.

Motivation & Objective

• To provide a detailed theoretical framework for the Higgs boson in the Standard Model, including its couplings and decay properties.
• To calculate and compare Higgs production cross sections at hadron colliders (LHC) and future lepton colliders (e+e−, γγ, μ+μ−).
• To develop precision measurement strategies for the Higgs boson's spin and CP quantum numbers using angular distributions and beam polarization.
• To assess the sensitivity of future colliders to detect and characterize the Higgs boson beyond the tree-level Standard Model predictions.
• To quantify the impact of QCD and electroweak radiative corrections on Higgs decay and production observables.

Proposed method

• Uses effective field theory and low-energy theorems to compute loop-induced decays (H→γγ, H→gg, H→γZ).
• Applies next-to-leading-order (NLO) QCD and electroweak corrections to Higgs production and decay amplitudes.
• Employs parton distribution functions (PDFs) and scale dependence analysis to estimate cross-section uncertainties at the LHC.
• Utilizes the effective longitudinal vector boson approximation to model vector boson fusion processes.
• Analyzes angular distributions and forward-backward asymmetries in H→τ+τ− decays at e+e− and muon colliders.
• Proposes beam polarization techniques (longitudinal and transverse) to enhance signal-to-background ratios and probe CP properties.

Experimental results

Research questions

• RQ1 What are the dominant production mechanisms for the Higgs boson at the LHC and future e+e− colliders?
• RQ2 How do QCD and electroweak radiative corrections affect Higgs decay branching ratios and production cross sections?
• RQ3 Can the Higgs boson's spin and CP quantum numbers be unambiguously determined using angular correlations and beam polarization?
• RQ4 What is the sensitivity of muon colliders to CP-odd components in the Higgs coupling to fermions?
• RQ5 How do experimental signatures and backgrounds differ for Higgs discovery and property measurements at various colliders?

Key findings

• The Higgs boson branching ratio into τ+τ− is measurable with ~20% statistical error at MH = 110 GeV using 1 fb⁻¹ luminosity and 25% beam polarization.
• For MH = 110 GeV, the signal-to-background ratio in µ+µ−→H→τ+τ− can be enhanced by up to a factor of 2.5 using longitudinal beam polarization.
• Transverse beam polarization at muon colliders can induce an asymmetry A1 = 2ab/(a² + b²) that distinguishes CP-even from CP-odd Higgs states.
• A non-zero asymmetry A1 > 0 indicates CP violation in the Higgs coupling, with A1 ≈ 1 for pure CP-odd or CP-even states.
• The spin correlation in τ+τ− final states allows clear discrimination between Higgs signal (Pτ⁻ = Pτ⁺ = ±1) and continuum background (Pτ⁻ = −Pτ⁺).
• For MH = 130 GeV, the statistical error on the Hτ+τ− coupling measurement reaches ~30%, enabling observable resonance above background.