Search for the pentaquark candidate $\Theta (1540){}^{+}$ in the hyperon beam experiment WA89

We report on a high-statistics search for the $\Theta (1540){}^{+}$ resonance in ${\Sigma }^{-}$-nucleus collisions at 340 GeV/c. No evidence for this resonance was found in our data sample which contains 13 million $K_s^0\to {\pi }^{+}{\pi }^{-}$ decays above background. For the decay channel ${\Theta }^{+}\to K_s^{0}p$ and the kinematic range $x_F>$ 0.05, we find the production cross section to be $\mathrm{BR}({\Theta }^{+}\to K_s^{0}p){\sigma }_0<1.8$ μb per nucleon at 99% C.L.

Figure 1

Summary of the first nine published observations of the $\Theta (1540){}^{+}$ resonance [1, 2, 3, 4, 5, 6, 7, 8, 9].

Figure 2

Reconstructed mass distribution m(${\pi }^{+}{\pi }^{-})-m(K_s^0)$ of $K_s^0$ candidates.

Figure 3

Invariant mass spectrum of all observed $K_s^{0}p$ candidates. Upper plot shows an extended view of the region around 1540 MeV/$c^2$. Statistical errors are approximately the size of the dots.

Figure 4

$x_F$ distribution for $K_s^{0}p$ pairs in the mass range $1500<m(K_s^{0}p)<1560$ MeV/$c^2$.