Limits for the Central Production ofΘ+andΞ--Pentaquarks in 920-GeV pA Collisions

We have searched for ${\Theta }^{+}$(1540) and ${\Xi }^{--}$(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and $\sqrt{s}=41.6\mathrm{G}\mathrm{e}\mathrm{V}$. In $2\times {10}^8$ inelastic events we find no evidence for narrow ($\sigma \approx 5\mathrm{M}\mathrm{e}\mathrm{V}$) signals in the ${\Theta }^{+}\to p{K}_S^0$ and ${\Xi }^{--}$ $\to$ ${\Xi }^{-}$ ${\pi }^{-}$ channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction $\mathcal{B}d\sigma /dy{|}_{y\approx 0}$ are $(4–16)\mu b/N$ for a ${\Theta }^{+}$ mass between 1521 and 1555 MeV, and $2.5\mu b/N$ for the ${\Xi }^{--}$. The UL of the yield ratio of ${\Theta }^{+}/\Lambda (1520)<(3–12)\%$ is significantly lower than model predictions. Our UL of $\mathcal{B}{\Xi }^{--}/\Xi (1530{)}^0<4\%$ is at variance with the results that have provided the first evidence for the ${\Xi }^{--}$.