摘要
The quark model based on quark–antiquark mesons and three-quark baryons has been very successful in classifying the hadrons.However,quantum chromodynamics(QCD)does not forbid the existence of exotic hadronic states with other quark–gluon configurations,such as
The quark model based on quark-antiquark mesons and three-quark baryons has been very successful in classifying the hadrons. However, quantum chromodynamics （QCD） does not forbid the existence of exotic hadronic states with other quark-gluon configurations, such as glueballs （with no quark）, hybrids （with quarks and excited gluon）, mul- tiquark states （with more than three quarks）, and hadron molecules （bound state of two or more hadrons）. It is a long history of searching for all these kinds of states; however, no solid conclusion was reached until the recent discovery of tetraquark and pentaquark states.
