Each type of nucleus contains a specific number of protons and a specific number of neutrons, and is called a nuclide or isotope. Hybrids consist of one or more valence quark-antiquark pairs and one or more real gluons.ДЄtomic nuclei consist of protons and neutrons.Glueballs are bound states of gluons with no valence quarks.Tetraquarks consist of two valence quarks and two valence antiquarks.Positive signatures have been reported for all of these particles at some time, but their existence is still somewhat uncertain. In quantum hadrodynamic models, the strong force between nucleons is mediated by mesons.Д®xotic mesons may also exist. Ordinary mesons ( bosons) contain a valence quark and a valence antiquark, and include the pion, kaon, the J/П€, and many other types of mesons. A 'sea' of virtual quark-antiquark pairs is also present in each hadron. Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks 'aces'), describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the colour force, which is mediated by gluons. Bosons, in which case they are called mesons.Fermions, in which case they are called baryons.Hadrons are defined as strongly interacting composite particles. The preon was a suggested substructure for both quarks and leptons, but modern collider experiments have all but disproven their existence. Tachyon is a generic name for hypothetical particles that travel faster than the speed of light and have an imaginary rest mass. Magnetic monopole is a generic name for particles with non-zero magnetic charge. Mirror particles are predicted by theories that restore Parity symmetry.

Sterile neutrinos are introduced by many extensions to the Standard Model, and may be needed to explain the LSND results.

The X boson and the Y boson are predicted by GUT theories to be heavier equivalents of the W and Z.

The saxion (spin-0, scalar, R parity=1) and the axino (spin-1/2, R parity = -1) form together with the axion a supermultiplet in supersymmetric extensions of Peccei-Quinn theory.

The axion (spin-0) is a pseudoscalar particle introduced in Peccei-Quinn theory to solve the strong-CP problem.

The graviscalar (spin-0) and graviphoton (spin-1).

The graviton (spin-2) has been proposed to mediate gravity in theories of quantum gravity.

$fundamental particles$

Other theories predict the existence of additional bosons. The stop squark (superpartner of the top quark) is thought to have a low mass and is often the subject of experimental searches.

Sleptons and squarks (spin-0) are the supersymmetric partners of the Standard Model fermions.

The gravitino (spin- 3вЃ„ 2) is the superpartner of the graviton boson in supergravity theories.

The photino (spin-ВЅ) is the superpartner of the photon.

The partners of charged bosons are called charginos. It is a leading candidate for dark matter.

The neutralino (spin-ВЅ) is a superposition of the superpartners of several neutral Standard Model particles.

Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally as of 2006. Many physicists expect the Higgs to be discovered at the Large Hadron Collider (LHC) particle accelerator now under construction at CERN. The intrinsic masses of the elementary particles (particularly the massive W В± and Z 0 bosons) would be explained by their interactions with this field. In the Higgs mechanism of the Standard Model, the massive Higgs boson is created by spontaneous symmetry breaking of the Higgs field. The Higgs boson (spin-0) is predicted by electroweak theory, and is the only Standard Model particle not yet observed. Leptons also exist in six flavours: Charged lepton / antiparticleД®lectron neutrino / Electron antineutrino Their respective antiparticles are known as antileptons (although the antiparticle of the electron is called the positron for historical reasons).

Leptons do not interact via the colour force.

Their respective antiparticles are known as antiquarks. According to the Standard Model, there are 12 flavours of elementary fermions: six quarks and six leptons. They are classified according to whether they interact via the colour force or not. Fermions are the basic building blocks of all matter. Each fermion has its own distinct antiparticle. Quark structure proton: 2 up quarks and 1 down quark.ДЇermions have half-integer spin for all known elementary fermions this is ВЅ.

Fundamental particles