A high-sensitivity search for the strangeness $S=-2\mathrm{}$ $H$ dibaryon $\left(\mathrm{uuddss}\right)$ was conducted at the Brookhaven Alternating Gradient Synchrotron (AGS) using the reaction ${}_{}{}^3{}_{}{}^{}H\mathrm{e}\left(K^{-}{,K}^{+}\right)\mathrm{Hn}$ at $P_{K^{-}}=1.8\mathrm{}\mathrm{GeV}/c$. The sensitivity was independent of $H$ lifetime and decay modes. No evidence for $H$ production was observed. In a mass range extending from about $50$ to $380\mathrm{MeV}{/c}^2$ below the $\Lambda \Lambda$ threshold of $2.231\mathrm{GeV}/c^2$, the resulting upper limits on the $H$-production cross section are in the range of $0.058$ to $0.021\mu \mathrm{b}/\mathrm{sr}$, approximately 1 order of magnitude below a theoretical calculation.

• Received 2 January 1997

DOI:https://doi.org/10.1103/PhysRevLett.78.3646