科研之友
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摘要
<正>For nearly forty years after the advent of the quark model [1,2],the only observed hadrons were mesons consistent with being a quark-antiquark(qq) pair and baryons consistent with being composed of three quarks(qqq). There was no reason why more ‘‘exotic" configurations, such as qqqq(tetraquarks) or qqqqq(pentaquarks), could not exist. Indeed, such a possibility was mentioned in the pioneering papers [1,2] and they had been predicted by such schemes as s–t channel duality in baryon-antibaryon scattering [3], the bag model of quark confinement [4–6], and binding of hadrons into molecules [7,8].
