Search for the Pentaquark via thePcs¯0→φπpDecay

We report results of the first search for the pentaquark $P_{\overline{c}s}$ which is predicted to be a doublet of states: $P_{\overline{c}s}^0=|\overline{c}\mathrm{suud}〉$ and $P_{\overline{c}s}^{-}=|\overline{c}\mathrm{sddu}〉$. A search was made for the decay $P_{\overline{c}s}^0\to \phi \pi p$ in data from Fermilab experiment E791, in which a $500\mathrm{GeV}/c$ ${\pi }^{-}$ beam interacted with nuclear targets. We present upper limits at 90% confidence level for the ratio of cross section times branching fraction of this decay to that for the decay $D_s^{\pm }\to \phi {\pi }^{\pm }$. The upper limits vary between 0.022 and 0.046 for $M\left(P_{\overline{c}s}^0\right)$ between $2.750$ and $2.907\mathrm{GeV}{/c}^2$, assuming a $P_{\overline{c}s}^0$ lifetime of 0.4 ps.