Search for an exotic $S=-2$, $Q=-2$ baryon resonance at a mass near 1862 MeV in quasireal photoproduction

A search for an exotic baryon resonance with $S=-2$, $Q=-2$ has been performed in quasireal photoproduction on a deuterium target through the decay channel ${\Xi }^{-}{\pi }^{-}\to \Lambda {\pi }^{-}{\pi }^{-}\to p{\pi }^{-}{\pi }^{-}{\pi }^{-}$. No evidence for a previously reported ${\Xi }^{--}(1860)$ resonance is found in the ${\Xi }^{-}{\pi }^{-}$ invariant mass spectrum. An upper limit for the photoproduction cross section of 2.1 nb is found at the 90% confidence level. The photoproduction cross section for the ${\Xi }^0(1530)$ is found to be between 9 and 24 nb.

Figure 1

(a) Invariant mass distribution of the $p{\pi }^{-}$ system. (b) Invariant mass distribution of the $p{\pi }^{-}{\pi }^{-}$ system. Both invariant mass distributions contain also the charge conjugate (c.c.) modes ($\overline{p}{\pi }^{+}$, $\overline{p}{\pi }^{+}{\pi }^{+}$) and are subject to the constraints in event topology discussed in the text.

Figure 2

Invariant mass distribution of the $p{\pi }^{-}{\pi }^{-}{\pi }^{-}$ system, subject to the constraints in event topology discussed in the text. The mixed-event background is represented by the gray shaded histogram, which is normalized to the background component of the fitted curve described in the text. The arrow shows the hypothetical ${\Xi }_{3/2}^{--}$ mass.

Figure 3

Invariant mass distribution of the $p{\pi }^{-}{\pi }^{-}{\pi }^{+}$ (plus c.c.) system, subject to the constraints in event topology discussed in the text. The mixed-event background is represented by the gray shaded histogram, which is normalized to the background component of the fitted curve described in the text. The arrow shows the hypothetical ${\Xi }_{3/2}^0$ mass. The excess near 1.77 GeV has a statistical significance of only $1.8\sigma$.