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Baryon number

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	Topics Baryon number Topic Home In particle physicsParticle physics Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactio... , the baryon number is an approximate conserved quantum numberQuantum number A quantum number describes the energies of electrons in atoms.... of a system. It is defined as: where is the number of quarks, and is the number of antiquarks. Why one third? According to the laws of strong interactionStrong interaction The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as ... there cannot be any bare color charge, i.e. the total color charge of a particle has to be zero ('white'), (cf. confinementColour confinement Colour confinement or color confinement is the physics phenomenon that colour charged particles cannot be isolated.... ). This can only be achieved by either putting together a quark of one color with an antiquark of the corresponding anti-color, giving a mesonMeson In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin.... with baryon number zero, by combining three quarks into a baryonBaryon In particle physics, the baryons are the family of subatomic particles which are made of three quarks.... with baryon number +1, or by combining three antiquarks into an anti-baryon with baryon number −1. Another possibility is the exotic pentaquarkPentaquark A pentaquark is an hypothetical subatomic particle consisting of a group of five quarks, or more specifically four quarks an... , thought to be found experimentally, which consists of 4 quarks and 1 anti-quark. Thus, quarks are always present in threes if antiquarks are counted as "negative quarks". Historically, baryon number was defined long before the current model of quarks was established, so rather than changing the definition, particle physicists simply divided the previously known quantum numberQuantum number Overview A quantum number describes the energies of electrons in atoms.... by three. Nowadays it might be more accurate to speak of the conservation of quark number. Particles without any quarks or antiquarks have a baryon number of zero. Such particles include leptonLepton In physics, a lepton is a particle with spin, 1/2 that does not experience the strong nuclear force.... s, the photonPhoton In modern physics, the photon is the elementary particle responsible for electromagnetic phenomena.... , and the W and Z bosonsW and Z bosons In physics, the W and Z bosons are the elementary particles that mediate the weak force.... . The baryon number is nearly conserved in all interactions of the Standard ModelStandard Model The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces,... . The loophole is the chiral anomalyChiral anomaly A chiral anomaly is the anomalous nonconservation of a chiral current.... . However, sphaleronSphaleron Overview A sphaleron is a static solution to the electroweak field equations of the Standard Model of particle physics, and it is inv... s are not all that common. Electroweak sphalerons can only change the baryon number by 3. 'Conserved' means that the sum of the baryon number of all incoming particles is the same as the sum of the baryon numbers of all particles resulting from the reaction. A violation of baryon number might lead to proton decay, but only if the baryon number changes by 1. The still hypothetical idea of grand unified theory allows for the changing of a baryonBaryon In particle physics, the baryons are the family of subatomic particles which are made of three quarks.... into a bunch of leptonLepton In physics, a lepton is a particle with spin, 1/2 that does not experience the strong nuclear force.... s, thus violating the conservation of baryon and lepton number. Proton decayFacts About Proton decay In particle physics, proton decay is an unobserved radioactive decay in which the proton decays into lighter subatomic parti... would be an example of such a process taking place. See also proton decayProton decay In particle physics, proton decay is an unobserved radioactive decay in which the proton decays into lighter subatomic parti... Lepton numberLepton number In high energy physics, the lepton number is the number of leptons minus the number of antileptons.... B-LB-L Overview In high energy physics, B-L is the baryon number minus the lepton number.... flavour (particle physics)Flavour (particle physics) Flavour, in the context of particle physics, is a quantum number of elementary particles related to their weak interactions.... IsospinIsospin In physics, and specifically, particle physics, isospin is a symmetry of the strong interaction as it applies to the interac... HyperchargeHypercharge In particle physics, the hypercharge of a particle is the sum of the baryon number B and the flavor charges: strangeness... External links