Search for Exotic Baryons in 800 GeV $pp\to p{\Xi }^{\pm }{\pi }^{\pm }X$ Reactions

We report the results of a high-statistics, sensitive search for narrow baryon resonances decaying to ${\Xi }^{-}{\pi }^{-}$, ${\Xi }^{-}{\pi }^{+}$, ${\overline{\Xi }}^{+}{\pi }^{-}$, and ${\overline{\Xi }}^{+}{\pi }^{+}$. The only resonances observed are the well known ${\Xi }^0(1530)$ and ${\overline{\Xi }}^0(1530)$. No evidence is found for the states near 1862 MeV, previously reported by NA49 [Phys. Rev. Lett. 92, 042003 (2003)]. At the 95% confidence level, we find the upper limit for the production of a Gaussian enhancement with $\sigma =7.6\mathrm{MeV}$ in the ${\Xi }^{-}{\pi }^{-}$ effective mass spectrum to be 0.3% of the number of observed ${\Xi }^0(1530)\to {\Xi }^{-}{\pi }^{+}$. We find similarly restrictive upper limits for an enhancement at 1862 MeV in the ${\Xi }^{-}{\pi }^{+}$, ${\overline{\Xi }}^{+}{\pi }^{-}$, and ${\overline{\Xi }}^{+}{\pi }^{+}$ mass spectra.

Figure 1

E690 multiparticle spectrometer.

Figure 2

Hyperon effective mass spectra in events used for this analysis: (a) ${\Xi }^{-}$, (b) ${\overline{\Xi }}^{+}$, (c) $\Lambda$ from ${\Xi }^{-}$ decay, and (d) $\overline{\Lambda }$ from ${\overline{\Xi }}^{+}$ decay. The full width at half maximum is 1.8 MeV for the $\Lambda$ and $\overline{\Lambda }$ and 2.6 MeV for the ${\Xi }^{-}$ ${\overline{\Xi }}^{+}$.

Figure 3

Effective mass spectra for: (a) ${\Xi }^{-}{\pi }^{+}$, (b) ${\overline{\Xi }}^{+}{\pi }^{-}$, (c) ${\Xi }^{-}{\pi }^{-}$, and (d) ${\overline{\Xi }}^{+}{\pi }^{+}$.

Figure 4

Fits to the $\Xi \pi$ effective mass spectra: (a) and (d) show the region near 1530 MeV. The superimposed curves show the background function and the sum of the background and a relativistic Breit-Wigner resonance, as described in the text. (b),(c),(e), and (f) show the region near 1862 MeV. The superimposed curves consist of the background function only.