Inclusive transverse momentum distribution of negative (top) and positive (bottom) muons at backward (left) and forward (right) rapidity in \pPb collisions at \eightnn. The results of the fit to the inclusive spectrum using a combination of MC templates is shown as a continuous line, the green, pink and blue dashed lines representing the contributions of the \W-, \Z/$\gamma^*$- and heavy-flavour hadron decay muons, respectively. The bottom panels show the ratio of the data to the fit result.