Figure 2

Invariant mass distributions for ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}} } = 2.76$ TeV and $-0.9< y< 0.9$ for events satisfying the event selection in Table 1, in the invariant mass range $2.2< M_{\rm inv}< 6$ GeV/$c^{2}$. Coherent enriched sample and incoherent enriched sample for muons and electrons are shown. Blue (red) circles (triangles) are opposite-sign (like-sign) pairs. For like-sign pair the penultimate cut in Table 1 is replaced by the request of a same-sign pair. No LS events were found for coherent di-electron events.