Elementary particle

[2] Among the 61 elementary particles embraced by the Standard Model number: electrons and other leptons, quarks, and the fundamental bosons.

In that year, Albert Einstein published his paper on Brownian motion, putting to rest theories that had regarded molecules as mathematical illusions.

[1][3] Subatomic constituents of the atom were first identified toward the end of the 19th century, beginning with the electron, followed by the proton in 1919, the photon in the 1920s, and the neutron in 1932.

[1] By that time, the advent of quantum mechanics had radically altered the definition of a "particle" by putting forward an understanding in which they carried out a simultaneous existence as matter waves.

Though extremely successful, the Standard Model is limited by its omission of gravitation and has some parameters arbitrarily added but unexplained.

[10] According to the current models of Big Bang nucleosynthesis, the primordial composition of visible matter of the universe should be about 75% hydrogen and 25% helium-4 (in mass).

[12] Other estimates imply that roughly 1097 elementary particles exist in the visible universe (not including dark matter), mostly photons and other massless force carriers.

[12] The Standard Model of particle physics contains 12 flavors of elementary fermions, plus their corresponding antiparticles, as well as elementary bosons that mediate the forces and the Higgs boson, which was reported on July 4, 2012, as having been likely detected by the two main experiments at the Large Hadron Collider (ATLAS and CMS).

[1] The Standard Model is widely considered to be a provisional theory rather than a truly fundamental one, however, since it is not known if it is compatible with Einstein's general relativity.

For example, the antielectron (positron) e+ is the electron's antiparticle and has an electric charge of +1 e. Isolated quarks and antiquarks have never been detected, a fact explained by confinement.

The Z0 does not convert particle flavor or charges, but rather changes momentum; it is the only mechanism for elastically scattering neutrinos.

The weak gauge bosons were discovered due to momentum change in electrons from neutrino-Z exchange.

This prediction was clearly confirmed by measurements of cross-sections for high-energy electron-proton scattering at the HERA collider at DESY.

On 4 July 2012, after many years of experimentally searching for evidence of its existence, the Higgs boson was announced to have been observed at CERN's Large Hadron Collider.

In particle physics, this is the level of significance required to officially label experimental observations as a discovery.

While it remains undiscovered due to the difficulty inherent in its detection, it is sometimes included in tables of elementary particles.

[17] Although experimental evidence overwhelmingly confirms the predictions derived from the Standard Model, some of its parameters were added arbitrarily, not determined by a particular explanation, which remain mysterious, for instance the hierarchy problem.

This breakdown is theorized to occur at high energies, making it difficult to observe unification in a laboratory.

The non-observation of proton decay at the Super-Kamiokande neutrino observatory rules out the simplest GUTs, however, including SU(5) and SO(10).

Such a symmetry predicts the existence of supersymmetric particles, abbreviated as sparticles, which include the sleptons, squarks, neutralinos, and charginos.

Due to the breaking of supersymmetry, the sparticles are much heavier than their ordinary counterparts; they are so heavy that existing particle colliders would not be powerful enough to produce them.

Accelerons are the hypothetical subatomic particles that integrally link the newfound mass of the neutrino to the dark energy conjectured to be accelerating the expansion of the universe.

[19] In this theory, neutrinos are influenced by a new force resulting from their interactions with accelerons, leading to dark energy.

[20] The most important address about the current experimental and theoretical knowledge about elementary particle physics is the Particle Data Group, where different international institutions collect all experimental data and give short reviews over the contemporary theoretical understanding.