(Top panel) The $\mathrm {\Xi}^{-}\mathrm {\pi^+}$invariant mass distribution in $\left | y \right | $ < 0.5 for the transverse momentum bin 1.2< $p_{\rm T}$< 1.6 GeV$\kern-0.15em /\kern-0.12em c$ in pp collisions at $\sqrt{s}$=7TeV The background shape estimated using pairs from different events (event-mixing) is shown as open red squares. The mixed-event background is normalized in the range 1.49< M< 1.51 GeV$\kern-0.15em /\kern-0.12em c^2$ (Bottom panel) The invariant mass distribution after mixed-event background subtraction for 1.2< $p_{\rm T}$ < 1.6 GeV$\kern-0.15em /\kern-0.12em c$ The solid curve is the result of the combined fit and the dashed line describes the residual background.