QGP tomography with photon tagged jets in ALICE
  $\gamma +$jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies. Tagging events with a well identified high $p_{T}$ direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon, allows us to determine, with a good approximation, both the jet fragmentation function and the back-to-back azimuthal misalignement of the direct photon and the jet. Comparing these two observables measured in $pp$ collisions with the ones measured in $AA$ collisions will reveal the modifications of the jet structure induced by the medium formed in $AA$ collisions and consequently will infer the medium properties. 
Yaxian Mao, Yves Schutz, Daicui Zhou, Christophe Furget and Gustavo   Conesa Balbastre
hep-ph