Combined yield of muons from \Wminus and \Wplus decays with $\pt^\mu >$ 10 \GeVc, normalised by the average number of binary nucleon--nucleon collisions \avNcollMult in \pPb collisions at \eightnn in the Pb-going (left) and p-going (right) configurations. The bars and boxes correspond to statistical and systematic uncertainties respectively. The horizontal dashed line indicates the central value of the yield normalised to \avNcollMult measured for the 0--100\% centrality interval.