Experimental limit on<i>ι→γγ</i>and the interpretation of the iota as a glueball

Abstract

By observing the reaction \ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}${K}_{s}^{0}$${K}^{\ifmmode\pm\else\textpm\fi{}}$${\ensuremath{\pi}}^{\ensuremath{\mp}}$, the TPC/Two-Gamma experiment at the SLAC ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ storage ring PEP has obtained a 95%-confidence-level limit of ${\ensuremath{\Gamma}}_{\ensuremath{\iota}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$B(\ensuremath{\iota}\ensuremath{\rightarrow}KK\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi})1.6 keV for the \ensuremath{\iota}(1450) meson. If, as is likely, the \ensuremath{\iota} decays predominantly into KK\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi}, the resulting ${\ensuremath{\Gamma}}_{\ensuremath{\iota}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$ limit appears to conflict with previous assignments of an observed \ensuremath{\rho}\ensuremath{\gamma} decay to \ensuremath{\iota} and also with many analyses of \ensuremath{\eta}-\ensuremath{\eta}'-\ensuremath{\iota} mixing. The contrast of this small \ensuremath{\gamma}\ensuremath{\gamma} width with the large rate for J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\iota} is evidence that the \ensuremath{\iota} is a glueball with little admixture of qq\ifmmode\bar\else\textasciimacron\fi{} states.