Subatomic Particle - History

History

In 1905, Albert Einstein demonstrated the physical reality of the photons, hypothesized by Max Planck in 1900, in order to solve the problem of black body radiation in thermodynamics.

In 1874, G. Johnstone Stoney postulated a minimum unit of electrical charge, for which he suggested the name electron in 1891. In 1897, J. J. Thomson confirmed Stoney's conjecture by discovering the first subatomic particle, the electron (now denoted e−). Subsequent speculation about the structure of atoms was severely constrained by Ernest Rutherford's 1907 gold foil experiment, showing that the atom is mainly empty space, with almost all its mass concentrated in a (relatively) tiny atomic nucleus. The development of the quantum theory led to the understanding of chemistry in terms of the arrangement of electrons in the mostly empty volume of atoms. In 1918, Rutherford confirmed that the hydrogen nucleus was a particle with a positive charge, which he named the proton, now denoted p+. Rutherford also conjectured that all nuclei other than hydrogen contain chargeless particles, which he named the neutron. It is now denoted n. James Chadwick discovered the neutron in 1932. The word nucleon denotes neutrons and protons collectively.

Neutrinos were postulated in 1931 by Wolfgang Pauli (and named by Enrico Fermi) to be produced in beta decays of neutrons, but were not discovered until 1956. Pions were postulated by Hideki Yukawa as mediators of the residual strong force, which binds the nucleus together. The muon was discovered in 1936 by Carl D. Anderson, and initially mistaken for the pion. In the 1950s the first kaons were discovered in cosmic rays.

The development of new particle accelerators and particle detectors in the 1950s led to the discovery of a huge variety of hadrons, prompting Wolfgang Pauli's remark: "Had I foreseen this, I would have gone into botany". The classification of hadrons through the quark model in 1961 was the beginning of the golden age of modern particle physics, which culminated in the completion of the unified theory called the standard model in the 1970s. The discovery of the weak gauge bosons through the 1980s, and the verification of their properties through the 1990s is considered to be an age of consolidation in particle physics. As of early 2012, of all the particles in the Standard Model, only the existence of the Higgs boson remained to be verified. On July 4th, 2012, CERN announced the discovery of a new particle, compatible with the Standard Model Higgs boson, through experiments conducted with the Large Hadron Collider.