Standard Model Higgs boson

Standard Model Higgs boson
Name	Standard Model Higgs boson
Mass	125.35 GeV/c² (approx.)
Charge	0 e
Discovered	2012
Discovered by	ATLAS experiment; CMS experiment
Theory by	Peter Higgs; François Englert; Robert Brout; Gerald Guralnik; C. R. Hagen; Tom Kibble

Standard Model Higgs boson The Standard Model Higgs boson is the scalar particle associated with the mechanism that gives mass to the W boson and Z boson while preserving gauge invariance in the Glashow–Weinberg–Salam model. It occupies a central role in the Standard Model and was predicted by work of Peter Higgs, François Englert, and collaborators; its observation by the ATLAS experiment and CMS experiment at the Large Hadron Collider in 2012 confirmed a long-standing theoretical prediction. Its properties, including mass, spin, and couplings, are subjects of precision tests by experiments such as ATLAS experiment, CMS experiment, Tevatron, and proposed facilities like the International Linear Collider.

Introduction

The Higgs boson emerges from the spontaneous symmetry breaking of the electroweak interaction via the Higgs mechanism, formulated in the 1960s by Peter Higgs, François Englert, Robert Brout, Gerald Guralnik, C. R. Hagen, and Tom Kibble. In the context of the Standard Model, the scalar field acquires a nonzero vacuum expectation value that generates masses for the W boson, Z boson, and fermions through Yukawa interactions; contemporaneous frameworks such as the Glashow–Weinberg–Salam model provided the gauge structure necessary for renormalizable electroweak unification tested at facilities including CERN and Fermilab. The boson’s discovery at the Large Hadron Collider culminated decades of work spanning collaborations like ATLAS experiment and CMS experiment and earned recognition in the form of the Nobel Prize in Physics.

Theoretical background

In the electroweak sector of the Standard Model the Higgs field is an SU(2) doublet whose potential leads to spontaneous symmetry breaking of the SU(2)×U(1) gauge symmetry. This construction follows from gauge theories developed by Sheldon Glashow, Steven Weinberg, and Abdus Salam in the Glashow–Weinberg–Salam model and incorporates renormalization techniques from work by Gerard 't Hooft and Martinus Veltman. The Higgs mechanism permits mass terms for the W boson and Z boson without explicit gauge-symmetry violation, while fermion masses arise via Yukawa couplings to the Higgs doublet as parameterized in the Cabibbo–Kobayashi–Maskawa matrix for quarks and the Pontecorvo–Maki–Nakagawa–Sakata matrix for leptons. The scalar self-coupling and vacuum expectation value determine the Higgs boson mass predicted within quantum corrections computed in perturbative Quantum Chromodynamics and electroweak loop diagrams involving particles such as the top quark and W boson.

Properties and interactions

The particle is a CP-even, spin-0 scalar with no electric charge; these quantum numbers distinguish it from gauge bosons like the photon and gluon and from fermions such as the electron and top quark. Its mass near 125 GeV was measured by the ATLAS experiment and CMS experiment using multiple final states; radiative corrections to this mass involve virtual contributions from heavy states including the top quark and hypothetical particles posited in extensions like supersymmetry. Couplings of the Higgs boson to fermions are proportional to fermion masses, a relation tested for particles such as the tau lepton, bottom quark, and top quark via associated production and decay channels. Gauge couplings to the W boson and Z boson are predicted by the electroweak symmetry-breaking structure and have been measured in vector-boson-fusion and associated-production processes at the Large Hadron Collider.

Production and decay modes

At high-energy colliders the dominant production mode at the Large Hadron Collider is gluon fusion mediated by a top-quark loop; alternative channels include vector-boson fusion, associated production with a W boson or Z boson (often denoted VH), and top-associated production (ttH). Decay modes depend on mass: for a 125 GeV boson principal observed decays include H→bb̄, H→τ+τ−, H→WW*, H→ZZ*, and the rare but clean H→γγ channel mediated by loop diagrams involving the W boson and top quark. Experimental analyses by ATLAS experiment, CMS experiment, and earlier searches at LEP and Tevatron combine channels to extract signal strengths relative to Standard Model expectations; differential measurements probe kinematic regimes and jet-associated signatures used by collaborations such as ATLAS experiment and CMS experiment.

Experimental discovery and measurements

Searches culminating in 2012 combined datasets from the ATLAS experiment and CMS experiment at the Large Hadron Collider to report a new resonance near 125 GeV in the γγ and ZZ*→4ℓ channels. The discovery built on exclusion limits set by LEP and the Tevatron and on theoretical predictions refined by groups working at CERN and international laboratories. Subsequent runs of the Large Hadron Collider improved measurements of mass, spin-parity, production cross sections, and branching ratios; precision fits confront predictions from global analyses by collaborations and theory groups including those around CERN and national laboratories such as Fermilab. Ongoing programs at the Large Hadron Collider and proposals like the High-Luminosity Large Hadron Collider aim to reduce uncertainties and to measure self-coupling via double-Higgs production and rare processes.

Role in beyond-Standard-Model physics

The measured mass and properties of the Higgs boson have profound implications for extensions of the Standard Model, influencing scenarios in supersymmetry, composite Higgs models, and theories addressing the hierarchy problem. The Higgs mass shapes vacuum-stability analyses connecting to the Planck scale and cosmological considerations studied by groups at institutions including CERN and Perimeter Institute. Precision deviations from Standard Model predictions could signal new dynamics such as extra dimensions explored in frameworks proposed by Arkani-Hamed, Savas Dimopoulos, and Nima Arkani-Hamed or new fermions in vector-like extensions examined at experiments like ATLAS experiment and CMS experiment. Future collider programs—International Linear Collider, Compact Linear Collider, and Future Circular Collider—are motivated in part by the need to probe Higgs couplings and self-interactions with higher precision.

Category:Elementary particles