Charmonium and $e^+e^-$ pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV

Understand

The ALICE Collaboration at the LHC has measured the J/$\psi$ and $\psi^{'}$ photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV.

• The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal.
• The analysis is based on an event sample corresponding to an integrated luminosity of about 23 $\mu\rm{b}^{-1}$.
• The cross section for coherent and incoherent J/$\psi$ production in the rapidity interval $-0.9<y<0.9$, are $\mathrm{d}\sigma_{{\rm J}/\psi}^{\rm coh}/\mathrm{d}y = 2.38^{+0.34}_{-0.24}\big(\mathrm{sta+sys}\big)$mb.