This particle is the heaviest theorized to occur in a stable three-particle mixture proposed by Bodler and Witten. The “eta–eta-prime puzzle” concerns two composite particles with different numbers of this particle. Pair production of this particle occurring from gluon fusion is used to determine the formation of QGPs. This particle occurs in the lightest lambda baryons. Electric charge and a property characterizing this particle were proposed to describe the “eightfold way” classification of (10[1])mesons and hadrons. This fundamental particle is the lightest to have an isospin of zero. The unusually long lifetime of kaons is due to this particle, since they consist of one of these second-generation particles along with an up or down quark. For 10 points, name this quark paired with charm. ■END■ (10[1])