stayParticle physicsIn the early period (the first half of the twentieth century), protons, neutronsPionwaithadronClass particles are considered as elementary particles.However, as more hadrons are discovered,Particle circleThe number of particles increased from a few in the early 1930s and 1940s to dozens in the 1950s.Physicians did not know their relationship until 1961 becauseMurray GelmanAndYuval NeymanEach independently proposes a hadron classification scheme called“Octet”, usingSU(3)Flavor symmetryThis problem was solved.
The eight fold way organizes hadrons into differentIsospin multipletHowever, physicists still do not know the physical principle behind this classification scheme.In 1964, Gelman andGeorge ZweigIndependent proposalQuark modelAt that time, only upper quark, lower quark andOdd quark。Although the quark model could reasonably explain the octet, there was no experimental evidence at that time.In 1968, physicistsStanford Linear Accelerator CenterThe experimental observations have finally confirmed the existence of lower quarks.Deep inelastic collisionThe experiment revealed that the proton has a secondary structure: it is composed of three more basic particles, thus confirming the quark model.
At first, people were reluctant to identify these three basic particles as quarks, but preferredRichard Feynman OfPartonModel.Over time, the quark model has gradually been widely accepted (see the entry for more detailsJ/ψ meson）。[1]
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Although lower quarks are common, lower quarkNaked massIt has not been accurately measured and should be between 4.5 and 5.3Mev/c ².Grid QCDThe value predicted by the method is more accurate: 4.79 ± 0.16Mev/c ².
staymeson(a particle consisting of a quark and an antiquark) orbaryon(particles composed of three quarks), the effective mass of quarks will become larger, which is attributed to theGluon fieldResultingbinding energy。For example, in the proton, the effective mass of the lower quark is about 330 Mev/c ².Since the naked mass of the lower quark is very small, it cannot be calculated directly because the relativistic effect must be taken into account.Under the strong force of the gluon field medium, the moving speed of quarks is about 99.995% of the speed of lightLorentz factorIt is about 100, so the total static mass of all quarks is only 1% of the mass of protons or neutrons.[1]
