Search for the exotic ${\Xi }^{--}\left(1860\right)$ resonance in $340\mathrm{GeV}∕c$ ${\Sigma }^{-}$-nucleus interactions

We report on a high statistics search for the ${\Xi }^{--}\left(1860\right)$ resonance in ${\Sigma }^{-}$-nucleus collisions at $340\mathrm{GeV}∕c$. No evidence for this resonance is found in our data sample which contains 676000 ${\Xi }^{-}$ candidates above background. For the decay channel ${\Xi }^{--}\left(1860\right)\to {\Xi }^{-}{\pi }^{-}$ and the kinematic range $0.15<x_F<0.9$ we find a $3\sigma$ upper limit for the production cross section of 3.1 and $3.5\mu \mathrm{b}$ per nucleon for reactions with carbon and copper, respectively.

Figure 1

Invariant mass distributions of $\Lambda {\pi }^{-}$ pairs with $p_{\Lambda \pi }<80\mathrm{GeV}∕c$ (solid histogram) and $<80\mathrm{GeV}∕c$ (dashed histogram) in $340\mathrm{GeV}∕c$ ${\Sigma }^{-}$ induced interactions.

Figure 2

Upper histogram: $x_F$ distribution of the observed ${\Xi }^{-}$ events within a $\pm 2\sigma$ mass window. Lower histogram: $x_F$ distribution of the observed ${\Xi }^{-}{\pi }^{-}$ pairs within the mass range between 1.82 and $1.90\mathrm{GeV}∕c^2$. In both cases the background has been subtracted by means of sideband events.

Figure 3

Effective mass distribution of ${\Xi }^{-}{\pi }^{-}$ combinations of all reactions, including also reactions in the tracking detectors $(\mathrm{Si}+\mathrm{C}+\mathrm{H})$ close to the C and Cu targets. Part (b) shows an extended view of the region around $1.862\mathrm{GeV}∕c^2$ marked by the arrows. Note the offset of the $y$-axis in this panel. In each panel the lower histogram shows the distribution after background subtraction via sidebands.

Figure 4

Effective mass distribution of ${\Xi }^{-}{\pi }^{-}$ combinations with $x_F\left({\Xi }^{-}{\pi }^{-}\right)⩽0.15$ (a), $x_F\left({\Xi }^{-}{\pi }^{-}\right)⩽0.3$ (b), and $x_F\left({\Xi }^{-}{\pi }^{-}\right)>0.3$ (c). In each plot the lower and upper histogram correspond to the carbon and copper target, respectively.