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In particle physics, an elementary particle or fundamental particle is a -->particle whose substructure is unknown, thus it is unknown whether it is composed of other particles.〔 〕 Known elementary particles include the fundamental fermions (quarks, leptons, antiquarks, and antileptons), which generally are "matter particles" and "antimatter particles", as well as the fundamental bosons (gauge bosons and Higgs boson), which generally are "force particles" that mediate interactions among fermions.〔 A particle containing two or more elementary particles is a ''composite particle''. Everyday matter is composed of atoms, once presumed to be matter's elementary particles—''atom'' meaning "indivisible" in Greek—although the atom's existence remained controversial until about 1910, as some leading physicists regarded molecules as mathematical illusions, and matter as ultimately composed of energy.〔〔 〕 Soon, subatomic constituents of the atom were identified. As the 1930s opened, the electron and the proton had been observed, along with the photon, the particle of electromagnetic radiation.〔 At that time, the recent advent of quantum mechanics was radically altering the conception of particles, as a single particle could seemingly span a field as would a wave, a paradox still eluding satisfactory explanation.〔 〕〔 〕〔 〕 Via quantum theory, protons and neutrons were found to contain quarks—up quarks and down quarks—now considered elementary particles.〔 And within a molecule, the electron's three degrees of freedom (charge, spin, orbital) can separate via wavefunction into three quasiparticles (holon, spinon, orbiton).〔 〕 Yet a free electron—which, not orbiting an atomic nucleus, lacks orbital motion—appears unsplittable and remains regarded as an elementary particle.〔 Around 1980, an elementary particle's status as indeed elementary—an ''ultimate constituent'' of substance—was mostly discarded for a more practical outlook,〔 embodied in particle physics' Standard Model, science's most experimentally successful theory.〔〔 〕 Many elaborations upon and theories beyond the Standard Model, including the extremely popular supersymmetry, double the number of elementary particles by hypothesizing that each known particle associates with a "shadow" partner far more massive,〔 〕〔 〕 although all such superpartners remain undiscovered.〔〔 〕 Meanwhile, an elementary boson mediating gravitation—the graviton—remains hypothetical.〔 == Overview == (詳細はspin''—either bosons or fermions. These are differentiated via the spin–statistics theorem of quantum statistics. Particles of ''half-integer'' spin exhibit Fermi–Dirac statistics and are fermions.〔 Particles of ''integer'' spin, in other words full-integer, exhibit Bose–Einstein statistics and are bosons.〔 ;Elementary fermions: *Matter particles * *Quarks: * * * up, down * * *charm, strange * * *top, bottom * *Leptons: * * *electron, electron neutrino (a.k.a., "neutrino") * * *muon, muon neutrino * * *tau, tau neutrino *Antimatter particles * *Antiquarks * *Antileptons ;Elementary bosons: *Force particles (gauge bosons): * *photon * * gluon (numbering eight)〔 * *''W''+, ''W''−, and ''Z''0 bosons * *graviton (hypothetical)〔 *Scalar boson * * Higgs boson A particle's mass is quantified in units of energy versus the electron's (electronvolts). Through conversion of energy into mass, any particle can be produced through collision of other particles at high energy,〔〔 although the output particle might not contain the input particles, for instance matter creation from colliding photons. Likewise, the composite fermions protons were collided at nearly light speed to produce the relatively more massive Higgs boson.〔 〕 The most massive elementary particle, the top quark, rapidly decays, but apparently does not contain, lighter particles. When probed at energies available in experiments, particles exhibit spherical sizes. In operating particle physics' Standard Model, elementary particles are usually represented for predictive utility as point particles, which, as zero-dimensional, lack spatial extension. Though extremely successful, the Standard Model is limited to the microcosm by its omission of gravitation, and has some parameters arbitrarily added but unexplained.〔 〕 Seeking to resolve those shortcomings, string theory posits that elementary particles are ultimately composed of one-dimensional energy strings whose absolute minimum size is the Planck length. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「elementary particle」の詳細全文を読む スポンサード リンク
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