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Search for formation of isospin-3/2 $Ξ$ states by neutrinos

A narrow peak near 1870 MeV is observed in the combined invariant-mass spectrum of the systems $ΛK^0_S π^-$, $ΛK^0_S π^+$, $ΛK^- π^-$, and $ΛK^- π^+$ formed in $ν_μ$- and $\bar{ν_μ}$-induced charged-current collisions with free protons, deuterons, and Neon nuclei. Observed width of the resonance is consistent with being entirely due to apparatus smearing. A possible interpretation of the peak is formation and three-body $ΛK π$ decay of an exotic baryon with $I = 3/2$ and $S = -2$.