Left: $\RAA$ of prompt $\rm D_s^+$ mesons in the 0-10% and 20-50% centrality classes as a function of $\pt$. For the 20-50% case, the symbols are displaced horizontally for visibility. Right: $\RAA$ of prompt $\rm D_s^+$ mesons compared to non-strange D mesons(average of $\Dzero$, $\Dplus$ and $\Dstar$) in the 0-10% centrality class. Statistical (bars), systematic (empty boxes), and normalisation (full box) uncertainties are shown.