The invariant mass distribution of $\Xi^-\pi^+ + \Xi^+\pi^-$ pairs in $|y|<0.5$ produced in pp collisions at $\sqrt{s} = 13$ TeV for $1.6 < < p_{\rm T,\Lambda\pi} < 2.0$ GeV/$c$ and the I+II+III multiplicity class (full black circles). The combinatorial background estimated with the event mixing technique is shown as open red squares in panel (a), whereas the invariant mass distribution after combinatorial background subtraction is shown in panel (b) together with the fits to the signal and the residual background contributions. The solid red curve is the result of the combined fit and the dashed black line represents the residual background.