Search for Light Gluinos via the Spontaneous Appearance of π+π- Pairs with an 800 GeV/c Proton Beam at Fermilab

We searched for the appearance of ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ pairs with invariant mass $\ensuremath{\ge}648\mathrm{MeV}{/c}^{2}$ in a neutral beam. Such an observation could signify the decay of a long-lived light neutral particle. We find no evidence for this decay. Our null result severely constrains the existence of an ${R}^{0}$ hadron, which is the lightest bound state of a gluon and a light gluino $(g\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g})$, and thereby also the existence of a light gluino. Depending on the photino mass, we exclude the ${R}^{0}$ in the mass and lifetime ranges of $1.2--4.6\mathrm{GeV}{/c}^{2}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}--7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\mathrm{s}$, respectively.