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

Abstract

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 \ensuremath{\psi} decay and double-Pomeron exchange. However, any meson of such a mass and quantum number has very restricted decay channels available---essentially only \ensuremath{\pi}\ensuremath{\pi} and, if the mass allows, KK\ifmmode\bar\else\textasciimacron\fi{}. In this case, any production process is very tightly correlated to elastic reactions, \ensuremath{\pi}\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi} and \ensuremath{\pi}\ensuremath{\pi}\ensuremath{\rightarrow}KK\ifmmode\bar\else\textasciimacron\fi{}, 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 \ensuremath{\pi}\ensuremath{\pi} and KK\ifmmode\bar\else\textasciimacron\fi{} final states. This unambiguously reveals three resonances in the 1-GeV region, ${S}_{1}$(991), ${S}_{2}$(988), and \ensuremath{\epsilon}(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 ${S}_{1}$(991) is a plausible candidate for the scalar glueball. We examine other production reactions (heavy-flavor decays and \ensuremath{\gamma}\ensuremath{\gamma} reactions) leading to the same final states, and discuss how, with future precision, these can probe fine details.