Invariant mass distribution of $\pi^{+}\pi^{-}$ pairs in $-0.5< y< 0$ after the like-sign background subtraction in p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The left (right) plot is obtained at low (high) $\pt$ of $\pi^+\pi^-$ pairs in minimum bias events. The abbreviation of Res. bkg represents the residual background