(a) Invariant-mass distribution of $\Xi^- \rightarrow \pi^-\Lambda$ (and charge conjugate) candidates integrated over \pt. The arrow indicates the world average $\Xi^-$ mass from Ref. and the dashed lines indicate the selected interval. (b) Invariant-mass distributions of right-sign and wrong-sign (and charge conjugate) pairs integrated over the whole \pt\ interval. The arrow indicates the \xicz\ mass .