The PDG Tables list more scalar mesons than can fit into one quark model nonet: indeed, even more than can belong to two multiplets. Consequently, some of these must be states beyond the quark model. So which of these is ${ \bar q}q$ or ${ \bar{ qq}}qq$ or multi-meson molecule or largely glue? How experiment can help us distinguish between these possibilities is discussed.
Categories: hep-ph