Meson dynamics beyond the quark model: Study of final-state interactions

A scalar glueball is predicted in the 1-GeV mass region. The present analysis is concerned with experimental evidence for such a state. It has been proposed that glueballs should be preferentially produced in supposedly glue-rich processes such as psi decay and double-Pomeron exchange. However, any meson of such a mass and quantum number has very restricted decay channels available: essentially only ππ and, if the mass allows, KK-bar. In this case, any production process is very tightly correlated to elastic reactions, ππ→ππ and ππ→KK-bar, by unitarity. Novel processes cannot then reveal effects that could not be seen in these elastic reactions. Nevertheless, they can valuably supplement this standard information where it lacks precision. Recent high-statistics results on central dimeson production at the CERN ISR enable us to perform an extensive new coupled-channel analysis of I = 0 S-wave ππ and KK-bar final states. This unambiguously reveals three resonances in the 1-GeV region, S1(991), S2(988), and ε(900), where the naive quark model expects just two. We discuss in detail these new features and how they may be confirmed experimentally, and give their present interpretation. The S1(991) is a plausible candidate for the scalar glueball. We examine other production reactions (heavy-flavor decays and γγ reactions) leading to the same final states, and discuss how, with future precision, these can probe fine details