A pile-up rejection procedure is applied to the set of **data** taken at √ s = 7 TeV: events with more than one distinct reconstructed primary vertex are rejected. This cut has a negligible effect on simulated events without pile-up: only 0.06% of the events are removed. We have compared a selection of high pile-up probability runs (see section 3) with a sample of low pile-up probability runs. The UE distributions differ by 20-25% between the two -4 - samples. After the above mentioned rejection procedure, the difference is reduced to less than 2%. Therefore, in the runs considered in the analysis, the effect of pile-up is negligible.