Acoplanarity of a Lepton Pair to Probe the Electromagnetic Property of Quark Matter

We investigate the P_T-broadening effects in dilepton production through photon-photon scattering in heavy ion collisions. The QED multiple interaction effect with the medium is found to be consistent with the recent observation of a low transverse momentum lepton pair from the ATLAS Collaboration at the LHC. We further comment on the magnetic broadening effect and point out a number of ways to disentangle these two mechanisms. In particular, the rapidity dependence of the P_T-broadening effect provides a unique probe to the magnetic effect.