Spin (physics) In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.[1][2] Spin is a solely quantum-mechanical phenomenon; it does not have a counterpart in classical mechanics (despite the term spin being reminiscent of classical phenomena such as a planet spinning on its axis).[2] Spin is one of two types of angular momentum in quantum mechanics, the other being orbital angular momentum. Orbital angular momentum is the quantum-mechanical counterpart to the classical notion of angular momentum: it arises when a particle executes a rotating or twisting trajectory (such as when an electron orbits a nucleus).[3][4] The existence of spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which particles are observed to possess angular momentum that cannot be accounted for by orbital angular momentum alone.[5] where h is the Planck constant.
List of particles This is a list of the different types of particles found or believed to exist in the whole of the universe. For individual lists of the different particles, see the individual pages given below. Elementary particles[edit] Fermions[edit] Fermions are one of the two fundamental classes of particles, the other being bosons. Fermions have half-integer spin; for all known elementary fermions this is 1⁄2. Quarks[edit] Leptons[edit] Bosons[edit] Bosons are one of the two fundamental classes of particles, the other being fermions. The fundamental forces of nature are mediated by gauge bosons, and mass is believed to be created by the Higgs Field. The graviton is added to the list[citation needed] although it is not predicted by the Standard Model, but by other theories in the framework of quantum field theory. Hypothetical particles[edit] Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally as of 2014: Composite particles[edit] Hadrons[edit]
Antimatter In particle physics, antimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but have opposite charge and other particle properties such as lepton and baryon number. Encounters between particles and antiparticles lead to the annihilation of both, giving rise to varying proportions of high-energy photons (gamma rays), neutrinos, and lower-mass particle–antiparticle pairs. Setting aside the mass of any product neutrinos, which represent released energy which generally continues to be unavailable, the end result of annihilation is a release of energy available to do work, proportional to the total matter and antimatter mass, in accord with the mass-energy equivalence equation, E=mc2.[1] Antiparticles bind with each other to form antimatter just as ordinary particles bind to form normal matter. Antimatter in the form of anti-atoms is one of the most difficult materials to produce. History of the concept Notation Origin and asymmetry Positrons
Fermion Type of subatomic particle In particle physics, a fermion is a particle that follows Fermi–Dirac statistics. Generally, it has a half-odd-integer spin: spin 1/2, spin 3/2, etc. These particles obey the Pauli exclusion principle. Fermions include all quarks and leptons and all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei. In addition to the spin characteristic, fermions have another specific property: they possess conserved baryon or lepton quantum numbers. As a consequence of the Pauli exclusion principle, only one fermion can occupy a particular quantum state at a given time. Composite fermions, such as protons and neutrons, are the key building blocks of everyday matter. English theoretical physicist Paul Dirac coined the name fermion from the surname of Italian physicist Enrico Fermi.[2] Elementary fermions[edit] The Standard Model recognizes two types of elementary fermions: quarks and leptons. Composite fermions[edit] See also[edit]
Spontaneous symmetry breaking Consider the bottom of an empty wine bottle, a symmetrical upward dome with a trough for sediment. If a ball is put in a particular position at the peak of the dome, the circumstances are symmetrical with respect to rotating the wine bottle. But the ball may spontaneously break this symmetry and move into the trough, a point of lowest energy. The bottle and the ball continue to have symmetry, but the system does not.[4] Most simple phases of matter and phase-transitions, like crystals, magnets, and conventional superconductors can be simply understood from the viewpoint of spontaneous symmetry breaking. Spontaneous symmetry breaking in physics[edit] Spontaneous symmetry breaking simplified: - At high energy levels (left) the ball settles in the center, and the result is symmetrical. Particle physics[edit] Chiral symmetry[edit] Chiral symmetry breaking is an example of spontaneous symmetry breaking affecting the chiral symmetry of the strong interactions in particle physics. , where .
neutrino muonique Définition, traduction, prononciation, anagramme et synonyme sur le dictionnaire libre Wiktionnaire. Français[modifier | modifier le wikicode] Étymologie[modifier | modifier le wikicode] Composé de neutrino et muonique. Locution nominale[modifier | modifier le wikicode] neutrino muonique masculin (Physique) En physique des particules, particule élémentaire, un type de neutrino, de charge électrique nulle et d'une masse presque égale à la moitié de celle de l'électron. Traductions[modifier | modifier le wikicode] Hyperonymes[modifier | modifier le wikicode] neutrino Voir aussi[modifier | modifier le wikicode] Neutrino sur Wikipédia Brane In string theory and related theories, D-branes are an important class of branes that arise when one considers open strings. As an open string propagates through spacetime, its endpoints are required to lie on a D-brane. The letter "D" in D-brane refers to the fact that we impose a certain mathematical condition on the system known as the Dirichlet boundary condition. The study of D-branes has led to important results, such as the anti-de Sitter/conformal field theory correspondence, which has shed light on many problems in quantum field theory. See also[edit] References[edit] Jump up ^ Moore, Gregory (2005).
Des neutrinos observés en pleine transformation Des neutrinos observés en pleine transformation Surnommées « particules fantômes » en raison de leurs interactions rarissimes avec la matière, les neutrinos sont très difficiles à observer. Or une collaboration internationale de physiciens vient non seulement de le faire mais surtout de détecter pour la première fois la transformation, ou « oscillation quantique de saveur », d’une forme de neutrinos particulière en une autre. Saveur Les neutrinos sont des particules principalement issues du coeur des étoiles. L’expérience qui a permis cette observation est installée sur deux sites différents. Oscillation Entre janvier 2010 et mars 2011, Super-Kamiokande a ainsi détecté 88 neutrinos créés par l’accélérateur de particules situé à Tokai. C’est dans l’observation expérimentale de l’apparition de neutrinos électroniques que réside la différence avec les travaux précédents. L’expérience japonaise permet également de confirmer que les neutrinos ont une masse. La Recherche Noter cet article :
String (physics) In physics, a string is a physical object that appears in string theory and related subjects. Unlike elementary particles, which are zero-dimensional or point-like by definition, strings are one-dimensional extended objects. Theories in which the fundamental objects are strings rather than point particles automatically have many properties that are expected to hold in a fundamental theory of physics. Most notably, a theory of strings that evolve and interact according to the rules of quantum mechanics will automatically describe quantum gravity. In string theory, the strings may be open (forming a segment with two endpoints) or closed (forming a loop like a circle) and may have other special properties. Prior to 1995, there were five known versions of string theory incorporating the idea of supersymmetry, which differed in the type of strings and in other aspects. As it propagates through spacetime, a string sweeps out a two-dimensional surface called its worldsheet.