Meson
Higher-energy (more massive) mesons were created momentarily in the Big Bang, but are not thought to play a role in nature today.Mesons are classified according to their quark content, total angular momentum, parity and various other properties, such as C-parity and G-parity.From theoretical considerations, in 1934 Hideki Yukawa[5][6] predicted the existence and the approximate mass of the "meson" as the carrier of the nuclear force that holds atomic nuclei together.Yukawa or Carl David Anderson, who discovered the muon, had originally named the particle the "mesotron", but he was corrected by the physicist Werner Heisenberg (whose father was a professor of Greek at the University of Munich).[8] The first candidate for Yukawa's meson, in modern terminology known as the muon, was discovered in 1936 by Carl David Anderson and others in the decay products of cosmic ray interactions.The "mu meson" had about the right mass to be Yukawa's carrier of the strong nuclear force, but over the course of the next decade, it became evident that it was not the right particle.There were years of delays in the subatomic particle research during World War II (1939–1945), with most physicists working in applied projects for wartime necessities.During 1939–1942, Debendra Mohan Bose and Bibha Chowdhuri exposed Ilford half-tone photographic plates in the high altitude mountainous regions of Darjeeling, and observed long curved ionizing tracks that appeared to be different from the tracks of alpha particles or protons.[9] This discovery was made in 1947 with improved full-tone photographic emulsion plates, by Cecil Powell, Hugh Muirhead, César Lattes, and Giuseppe Occhialini, who were investigating cosmic ray products at the University of Bristol in England, based on photographic films placed in the Andes mountains.Spin (quantum number S) is a vector quantity that represents the "intrinsic" angular momentum of a particle.Gravity, the electromagnetic force, and the strong interaction all behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said to conserve parity (P-symmetry).It turns out that this is not quite true: In order for the equations to be satisfied, the wavefunctions of certain types of particles have to be multiplied by −1, in addition to being mirror-reversed.CP-parity was originally thought to be conserved, but was later found to be violated on rare occasions in weak interactions.The concept of isospin was first proposed by Werner Heisenberg in 1932 to explain the similarities between protons and neutrons under the strong interaction.For example, the three pions all have different charges but they all have similar masses (c. 140 MeV/c2) as they are each composed of a same total number of up and down quarks and antiquarks.Isospin, although conveying an inaccurate picture of things, is still used to classify hadrons, leading to unnatural and often confusing nomenclature.Particles could be described with isospin projections (related to charge) and strangeness (mass) (see the uds nonet figures).As other quarks were discovered, new quantum numbers were made to have similar description of udc and udb nonets.If the quarks all had the same mass, their behaviour would be called symmetric, because they would all behave in exactly the same way with respect to the strong interaction.In table form, they are:[24] There is experimental evidence for particles that are hadrons (i.e., are composed of quarks) and are color-neutral with zero baryon number, and thus by conventional definition are mesons.
Meson (software)compositequarksantiquarksStatisticsbosonichadronInteractionsstrongelectromagneticgravityHideki YukawaElectric chargeparticle physicshadronicsubatomic particlestrong interactionfemtometreprotonneutronelectronsneutrinosphotonscosmic raysbaryonic mattercyclotronsparticle acceleratorsantiprotonsBig Bangbaryonsexotic mesonsbosonsfermionsantiparticleweak interactionelectric chargeelectromagnetic interactiontotal angular momentumparityC-parityG-paritycosmic rayJ/Psi mesoncharm quarkupsilon mesonbottom quarknuclear forceatomic nucleiprotonsYukawaCarl David AndersonWerner HeisenbergUniversity of Munichdecay products"mu meson"electronleptonWorld War II"pi meson"Debendra Mohan BoseBibha ChowdhuriIlfordhalf-toneDarjeelingNatureCecil PowellHugh MuirheadCésar LattesGiuseppe OcchialiniUniversity of BristolEnglandRobert Marshakvirtual particleneutronsrho mesonsNobel Prize in Physics"the Z0 meson"Spin (physics)angular momentum operatorQuantum numbersvectorangular momentumvector mesonspin-1scalar mesonspin-0scalar mesonspseudoscalar mesonsmeson spectroscopyParity (physics)"parity"electromagnetic forceconserve parityparity violationwavefunctionquantum fieldspherical harmonicDirac equationCP-parityweak interactionsIsospinEugene Wignercharged staterho particleMurray Gell-Mannquark modelquantum superpositionstrangenessquantum numberbrokenbaryon numberGell-Mann–Nishijima formulabottomnesstopnessList of mesonsParticle Data GroupPseudoscalar mesonPseudovector mesonflavour quantum numbersspectroscopic stateground stateExotic mesonhadronsZ(4430)Belle experimenttetraquark