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Physics › Particle Physics

Higgs Boson Discovery and Properties

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Higgs MechanismStandard Model Overview+1 more→→Beyond Standard Model (BSM) Overview
higgs-boson lhc higgs-discovery higgs-couplings

Core Idea

The Higgs boson was discovered at the LHC in 2012 by the ATLAS and CMS experiments, with a mass of 125.1 GeV. Its production and decay rates are consistent with Standard Model predictions: it is a spin-0, CP-even scalar whose couplings to other particles are proportional to their masses. Measuring the Higgs couplings with increasing precision is the central goal of the LHC program and future colliders.

Explainer

The discovery of the Higgs boson on July 4, 2012, by the ATLAS and CMS experiments at the LHC was the culmination of a nearly 50-year search. The particle was predicted in 1964 by Brout, Englert, and Higgs as a consequence of the mechanism that gives mass to the W and Z bosons. Its mass of 125.1 GeV, while not predicted by the Standard Model, turns out to be in a theoretically interesting range: heavy enough to be discovered at the LHC but light enough to leave the Standard Model perturbative up to very high energy scales.

The production mechanisms at the LHC reflect the Higgs coupling structure. Gluon fusion (gg -> H via a top loop) dominates because of the large gluon luminosity and the strong top Yukawa coupling. Vector boson fusion (qq -> qqH via W/Z exchange) has a distinctive signature of two forward jets with a rapidity gap. Associated production (WH, ZH, ttH) provides direct access to the HWW, HZZ, and Htt couplings. Each production mode has been observed and measured, confirming the expected coupling pattern.

The decay modes span a wide range of branching ratios. The dominant decay is H -> bb (58%), followed by H -> WW* (21%), H -> gg (8.2%), H -> tau tau (6.3%), H -> cc (2.9%), H -> ZZ* (2.6%), H -> gamma gamma (0.23%), H -> Z gamma (0.15%), and H -> mu mu (0.02%). The hierarchy of branching ratios directly reflects the mass-proportional coupling: the Higgs decays predominantly to the heaviest particles that are kinematically accessible. The rare decays H -> gamma gamma and H -> Z gamma are loop-induced (like gg -> H) and are sensitive to virtual particles in the loop, including potential new charged particles beyond the Standard Model.

The future Higgs program aims to measure all couplings at the percent level or better and to observe the Higgs self-coupling (the trilinear HHH coupling, which determines the shape of the Higgs potential). The HL-LHC (High-Luminosity LHC, starting ~2029) will collect 20 times more data, enabling 3-5% coupling measurements and a first look at Higgs pair production. Proposed future colliders -- the FCC-ee (e+e- at 240 GeV), ILC, CLIC, CEPC, and the FCC-hh (100 TeV pp) -- could measure couplings to sub-percent precision and determine the Higgs self-coupling to 5-10%. Any deviation from the Standard Model prediction would point to new physics in the Higgs sector, such as additional scalar fields, compositeness, or supersymmetry.

Practice Questions 4 questions

Prerequisite Chain

Understanding Zero → The Number Zero → Counting to Five → Counting to 10 → One-to-One Correspondence → Counting a Set of Objects Up to 20 → Cardinality: The Last Number Counted → Matching Numerals to Quantities → Subitizing Small Quantities → Addition Within 10 → Making 10 as an Addition Strategy → Addition Within 20 → Doubles and Near Doubles → Doubles Facts Within 10 → Near Doubles Facts Within 20 → Mental Math Strategies for Addition → Mental Math: Adding and Subtracting Tens → Addition Within 100 → Repeated Addition as Multiplication → Multiplication as Equal Groups → Multiplication: Arrays → Basic Multiplication Facts (0s, 1s, 2s, 5s, 10s) → Multiplication Facts Within 100 → Division as Equal Sharing → Division as Grouping (Measurement Division) → Division: Grouping (Repeated Subtraction) Model → Division: Fair Sharing Model → Division as Equal Sharing → Division as Grouping → Basic Division Facts → Division Facts Within 100 → Multiplication and Division Fact Families → Relationship Between Multiplication and Division → Division Facts as Inverse of Multiplication → Remainders and Quotients in Division → Division Word Problems → Multi-Step Word Problems → Solving Multi-Step Word Problems → Multiplication Word Problems → Division Word Problems → Introduction to Long Division → Factors and Multiples → Prime and Composite Numbers → Equivalent Fractions → Relating Fractions and Decimals → Decimal Place Value → Integers and the Number Line → Comparing and Ordering Integers → Absolute Value → Adding Integers → Subtracting Integers → Multiplying Integers → Dividing Integers → Unit Rates → Proportions → Percent Concept → Converting Between Fractions, Decimals, and Percents → Operations with Rational Numbers → Two-Step Equations → Solving Multi-Step Equations → Equations with Variables on Both Sides → Angle Pairs: Complementary, Supplementary, and Vertical → Parallel Lines and Transversals → Corresponding Angles → Alternate Interior Angles → Triangle Angle Sum Theorem → Exterior Angle Theorem → Triangle Inequality Theorem → Similar Triangles: AA Similarity → Similar Triangles: SSS and SAS Similarity → Proportions in Similar Triangles → Right Triangle Trigonometry Introduction → Sine, Cosine, and Tangent Ratios → Trigonometric Ratios Review → Radian Measure → Converting Between Degrees and Radians → The Unit Circle → Graphing Sine and Cosine → Graphing Tangent and Reciprocal Trigonometric Functions → Derivatives of Trigonometric Functions → Antiderivatives → Iterated Integrals and Fubini's Theorem → Double Integrals in Cartesian Coordinates → Double Integrals in Polar Coordinates → Double Integrals in Polar Coordinates → Double Integrals: Definition and Setup → Iterated Integrals and Fubini's Theorem → Double Integrals over Rectangular Regions → Double Integrals over General Regions → Applications of Double Integrals: Area, Mass, and Moments → Triple Integrals in Cartesian Coordinates → Triple Integrals in Cylindrical and Spherical Coordinates → Change of Variables and the Jacobian Determinant → Applications of Triple Integrals: Volume and Mass → Vector Fields and Their Representations → Line Integrals of Vector Fields → Work and Circulation → Line Integrals of Scalar and Vector Functions → Fundamental Theorem for Line Integrals → Conservative Vector Fields → Conservative Vector Fields and Potential Functions → Curl and Divergence of Vector Fields → Curl and Divergence → Divergence Theorem → Electric Flux and Divergence Theorem → Gauss's Law: Integral Form and Meaning → Solving Problems with Gauss's Law → Conductors in Electrostatic Equilibrium → Capacitance and Capacitors → Dielectrics → Dielectric Constant and Relative Permittivity → Electric Field Inside Dielectric Materials → Dielectric Materials and Polarization → Dielectric Susceptibility and Permittivity → Energy Density in Electric Fields → Electric Current and Current Density → Electrical Resistance and Resistivity → Ohm's Law and Circuit Elements → Electromotive Force (EMF) and Batteries → Kirchhoff's Circuit Laws: Voltage and Current → DC Circuit Network Analysis Methods → Transient Response in RC Circuits → RC Circuits → LC and RLC Circuits → AC Circuits: Fundamentals → Impedance and Reactance → AC Power and Resonance → Electromagnetic Waves → Postulates of Special Relativity → Time Dilation → Length Contraction → Lorentz Transformation → Relativistic Velocity Addition → Relativistic Momentum and Energy → Mass-Energy Equivalence and E=mc² → Photons as Particles with Energy and Momentum → Planck-Einstein Relation: Energy and Frequency → Photoelectric Effect → The Photon: Light as Quanta → Compton Scattering → Wave-Particle Duality → de Broglie Wavelength → The Schrödinger Equation → State Vectors and Wavefunctions → Quantum Superposition → The Measurement Problem → Interpretations of Quantum Mechanics → Postulates of Quantum Mechanics → Observables and Quantum Operators → Commutators and Commutation Relations → Quantum Angular Momentum → Quantum Mechanical Treatment of Hydrogen → Solving the Schrödinger Equation for Hydrogen Atom → Quantum Numbers → Electron Configuration → Periodic Trends → Covalent Bonding → Electronegativity and Bond Polarity → Ionic Bonding → Lewis Structures → VSEPR Theory and Molecular Geometry → Molecular Geometry and Electron Pair Geometry → Molecular Polarity and Dipole Moments → Intermolecular Forces → States of Matter and Phase Changes: Melting, Boiling, and Sublimation → Gas Laws and the Ideal Gas Equation → Gas Stoichiometry and Volume-Volume Calculations → Thermochemistry and Enthalpy → Heat Capacity and Calorimetry → Entropy and Molecular Disorder → Spontaneity and ΔG → Entropy and Gibbs Free Energy → Chemical Equilibrium → Statistical Mechanics: Ensembles and the Boltzmann Distribution → Partition Function: Definition and Properties → Helmholtz Free Energy → Gibbs Free Energy → Phase Transitions: First Order and Second Order → Critical Phenomena and Critical Exponents → Landau Theory of Phase Transitions → Symmetry Breaking and Phase Transitions → Goldstone's Theorem and Gapless Modes → Goldstone Theorem → Higgs Mechanism → Electroweak Unification → Standard Model Overview → Collider Physics Methods → Cross Section Measurements → Higgs Boson Discovery and Properties

Longest path: 189 steps · 1269 total prerequisite topics

Prerequisites (3)

Higgs Mechanismhard Standard Model Overviewhard Cross Section Measurementssoft

Leads To (1)

Beyond Standard Model (BSM) Overviewhard