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In particle physics, the baryon number is a strictly conserved additive quantum number of a system. It is defined as :: where ''n''q is the number of quarks, and ''n'' is the number of antiquarks. Baryons (three quarks) have a baryon number of +1, mesons (one quark, one antiquark) have a baryon number of 0, and antibaryons (three antiquarks) have a baryon number of −1. Exotic hadrons like pentaquarks (four quarks, one antiquark) and tetraquarks (two quarks, two antiquarks) are also classified as baryons and mesons depending on their baryon number. ==Baryon number vs. quark number == Quarks carry not only electric charge, but also charges such as color charge and weak isospin. Because of a phenomenon known as ''color confinement'', a hadron cannot have a net color charge; that is, the total color charge of a particle has to be zero ("white"). A quark can have one of three "colors", dubbed "red", "green", and "blue". For normal hadrons, a white color can thus be achieved in one of three ways: *A quark of one color with an antiquark of the corresponding anticolor, giving a meson with baryon number 0, *Three quarks of different colors, giving a baryon with baryon number +1, *Three antiquarks into an antibaryon with baryon number −1. The baryon number was defined long before the quark model was established, so rather than changing the definitions, particle physicists simply gave quarks one third the baryon number. Nowadays it might be more accurate to speak of the conservation of quark number. In theory, exotic hadrons can be formed by adding pairs of quark and antiquark, provided that each pair has a matching color/anticolor. For example, a pentaquark (four quarks, one antiquark) could have the individual quark colors: red, green, blue, blue, and antiblue. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「baryon number」の詳細全文を読む スポンサード リンク
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