Strong interaction

Strong interaction
Name	Strong interaction
Other names	Strong force, Strong nuclear force, Strong interaction (quantum)
Field	Particle physics
Discovered	1932
Discoverers	Hideki Yukawa, Ernest Rutherford, Werner Heisenberg
Mediators	Gluons
Carriers	Gluons
Constituents	Quarks
Theory	Quantum Chromodynamics

Strong interaction The strong interaction is the fundamental force responsible for binding protons and neutrons in atomic nuclei and for confining quarks inside hadrons. It is described by Quantum Chromodynamics within the Standard Model and underlies phenomena studied at facilities such as CERN, Fermilab, and DESY. Historic experiments at institutions like Brookhaven National Laboratory and theoretical work by figures including Murray Gell-Mann, Richard Feynman, and Yoichiro Nambu shaped current understanding.

Introduction

The identification of a force capable of binding nucleuss followed discoveries by Ernest Rutherford and theoretical proposals by Hideki Yukawa that predicted a carrier particle before the discovery of the pion at Cosmic ray experiments and later accelerator studies at Cavendish Laboratory and Lawrence Berkeley National Laboratory. Developments by Werner Heisenberg and Enrico Fermi contributed to nuclear theory, while later work at SLAC and Stanford Linear Accelerator Center revealed partonic structure that linked to the strong force. The formulation of a gauge theory by theorists including Murray Gell-Mann, George Zweig, and Frank Wilczek led to Quantum Chromodynamics as part of the Standard Model used by collaborations at ATLAS (experiment), CMS, and LHCb.

Theoretical Framework (Quantum Chromodynamics)

Quantum Chromodynamics (QCD) is a non-Abelian gauge theory based on the SU(3) symmetry group developed by Murray Gell-Mann and Harald Fritzsch with contributions from Frank Wilczek, David Gross, and H. David Politzer who demonstrated asymptotic freedom. The theory posits eight massless gluon fields mediating interactions among six flavors of quarks discovered through experiments by teams at SLAC, DESY, and CERN; quark flavors include up quark, down quark, strange quark, charm quark, bottom quark, and top quark. Lattice QCD, pioneered at institutions like IBM Research and advanced by collaborations such as the MILC Collaboration and CP-PACS, provides nonperturbative numerical solutions used to calculate hadron spectra measured by experiments like Belle and BaBar. Renormalization group analysis by Kenneth Wilson and operator product expansion techniques by Kenneth G. Wilson and John C. Collins underpin perturbative calculations applied in scattering experiments at Tevatron and LHC.

Properties and Interactions (Confinement, Asymptotic Freedom, Color Charge)

Confinement, asymptotic freedom, and color charge are central properties developed in work by Yoichiro Nambu, Gerard 't Hooft, and Murray Gell-Mann. Color charge in QCD is analogous to electric charge in James Clerk Maxwell's electromagnetic theory but realized as three-valued charge carried by quarks and gluons; experimental signatures were first inferred from deep inelastic scattering at SLAC and from jet physics at CERN and PETRA. Asymptotic freedom, proven by David Gross, Frank Wilczek, and H. David Politzer, explains why quarks behave nearly free at high momentum transfer observed in experiments at HERA and RHIC. Confinement manifests in hadronization processes studied by collaborations at LEP and in heavy-ion collisions at ALICE (experiment) and Brookhaven National Laboratory's RHIC (Relativistic Heavy Ion Collider) where quark-gluon plasma signatures were sought by teams including STAR Collaboration and PHENIX.

Hadrons and Nuclear Forces

Hadrons, including protons, neutrons, mesons such as the pion and kaon, arise from quark combinations bound by gluon exchange; classification schemes were established by Murray Gell-Mann and Yuval Ne'eman via the Eightfold Way and later formalized by the Particle Data Group. Nuclear forces between nucleons are residual effects of QCD analogous to Van der Waals forces; effective theories like chiral perturbation theory developed by Steven Weinberg and Jürg Gasser describe low-energy nucleon interactions used in modeling nuclear structure investigated at Oak Ridge National Laboratory and Los Alamos National Laboratory. Exotic hadrons, such as tetraquarks and pentaquarks reported by LHCb and earlier hints from Belle and BESIII, challenge quark model classifications proposed by Isidor Rabi's successors.

Experimental Evidence and Measurements

Evidence for the strong interaction spans discoveries from cloud chamber observations by C. T. R. Wilson to collider measurements at CERN, SLAC, Fermilab, and DESY. Deep inelastic scattering at SLAC established quark partons, while jet production studies at PETRA and LEP confirmed gluon radiation. Precision measurements of the strong coupling constant alpha_s come from global fits combining results from ALEPH, OPAL, ATLAS (experiment), and CMS as well as lattice QCD results from collaborations like UKQCD and JLQCD. Heavy-ion experiments at CERN SPS, RHIC, and LHC probe quark-gluon plasma and transport properties analyzed by groups including ALICE (experiment) and CMS. Proton structure functions measured by H1 (experiment) and ZEUS at HERA inform parton distribution functions used in predictions for Tevatron and LHC processes.

Applications and Implications (Astrophysics, Particle Physics)

In astrophysics, the strong interaction governs the equation of state of dense matter in neutron stars studied by observatories such as LIGO and NICER and theoretical groups at Max Planck Institute for Astrophysics and Institute for Advanced Study. Nucleosynthesis in supernovae and early-universe conditions depends on nuclear reactions characterized at TRIUMF and ISOLDE. In particle physics, understanding QCD is crucial for searches for physics beyond the Standard Model pursued by collaborations including ATLAS (experiment), CMS, and experiments at KEK. Applications extend to technologies developed at national laboratories like Argonne National Laboratory and Lawrence Livermore National Laboratory and inform precision tests of symmetry by groups working on CP violation using experiments such as NA48 and KTeV.

Category:Particle physics