Figure 5: Invariant mass distributions for photon pairs accepted by the on-line πstream for
the data and simulations in the EB (left) and in the EE (right). The distributions for data are
obtained with 18.7 nb−1 . The number of events in the simulation distribution is normalized to
that for the data. In addition, the difference between data and simulation observed for EB and
EE energy scales with the off-line analysis (see Section 4.4) are also corrected for. Here and in
the following the ﬁtted peak width is given as a fraction of the ﬁtted peak position.