<P> Zweig preferred the name ace for the particle he had theorized, but Gell - Mann's terminology came to prominence once the quark model had been commonly accepted . </P> <P> The quark flavors were given their names for several reasons . The up and down quarks are named after the up and down components of isospin, which they carry . Strange quarks were given their name because they were discovered to be components of the strange particles discovered in cosmic rays years before the quark model was proposed; these particles were deemed "strange" because they had unusually long lifetimes . Glashow, who co-proposed charm quark with Bjorken, is quoted as saying, "We called our construct the' charmed quark', for we were fascinated and pleased by the symmetry it brought to the subnuclear world ." The names "bottom" and "top", coined by Harari, were chosen because they are "logical partners for up and down quarks". In the past, bottom and top quarks were sometimes referred to as "beauty" and "truth" respectively, but these names have somewhat fallen out of use . While "truth" never did catch on, accelerator complexes devoted to massive production of bottom quarks are sometimes called "beauty factories". </P> <P> Quarks have fractional electric charge values--either (− ​ ⁄) or (+ ​ ⁄) times the elementary charge (e), depending on flavor . Up, charm, and top quarks (collectively referred to as up - type quarks) have a charge of + ​ ⁄ e, while down, strange, and bottom quarks (down - type quarks) have − ​ ⁄ e . Antiquarks have the opposite charge to their corresponding quarks; up - type antiquarks have charges of − ​ ⁄ e and down - type antiquarks have charges of + ​ ⁄ e . Since the electric charge of a hadron is the sum of the charges of the constituent quarks, all hadrons have integer charges: the combination of three quarks (baryons), three antiquarks (antibaryons), or a quark and an antiquark (mesons) always results in integer charges . For example, the hadron constituents of atomic nuclei, neutrons and protons, have charges of 0 e and + 1 e respectively; the neutron is composed of two down quarks and one up quark, and the proton of two up quarks and one down quark . </P> <P> Spin is an intrinsic property of elementary particles, and its direction is an important degree of freedom . It is sometimes visualized as the rotation of an object around its own axis (hence the name "spin"), though this notion is somewhat misguided at subatomic scales because elementary particles are believed to be point - like . </P>

An antibaryon composed of two anti up quarks and one antidown quark
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