Hypercharge

In particle physics, the hypercharge (a portmanteau of hyperonic and charge) Y of a particle is a quantum number conserved under the strong interaction. The concept of hypercharge provides a single charge operator that accounts for properties of isospin, electric charge, and flavour. The hypercharge is useful to classify hadrons; the similarly named weak hypercharge has an analogous role in the electroweak interaction. Hypercharge is one of two quantum numbers of the SU(3) model of hadrons, alongside isospin I_3. The isospin alone was sufficient for two quark flavours — namely _up quark and _down quark — whereas presently 6 flavours of quarks are known. SU(3) weight diagrams (see below) are 2 dimensional, with the coordinates referring to two quantum numbers: I_3 (also known as I_z), which is the z component of isospin, and Y, which is the hypercharge (defined by strangeness S, charm C, bottomness B′, topness T′, and baryon number B). Mathematically, hypercharge is Strong interactions conserve hypercharge (and weak hypercharge), but weak interactions do not. Gell-Mann–Nishijima formula The Gell-Mann–Nishijima formula relates isospin and electric charge where I3 is the third component of isospin and Q is the particle's charge. Isospin creates multiplets of particles whose average charge is related to the hypercharge by: since the hypercharge is the same for all members of a multiplet, and the average of the I3 values is 0. These definitions in their original form hold only for the three lightest quarks. The SU(2) model has multiplets characterized by a quantum number J, which is the total angular momentum. Each multiplet consists of 2J + 1 substates with equally-spaced values of Jz, forming a symmetric arrangement seen in atomic spectra and isospin. This formalizes the observation that certain strong baryon decays were not observed, leading to the prediction of the mass, strangeness and charge of the _Omega- baryon. The SU(3) has supermultiplets containing SU(2) multiplets.