Prospects of medium tomography using back-to-back hadron correlations
  We discuss the prospects of extracting information about the bulk QCD matter distribution and evolution on the basis of hard hadronic back-to-back correlations in ultrarelativistic heavy-ion collisions. Using both hydrodynamical and parametrized evolution models for the spacetime evolution of the produced matter, which have been tested against RHIC data, we study six different setups for the spacetime dependence of hard-parton energy losses. Assuming that the energy loss of hard partons traversing the medium is radiative and calculable in the BDMPS formalism, we adjust one parameter, the quenching power scale, to the measured R_AA in each of the setups and study the systematic variations of the back-to-back yield as a function of p_T. We show which spacetime regions are probed by one-particle and two-particle observables and study the role of longitudinal and transverse expansion in some detail. We also comment on the importance of considering fluctuations around the average energy loss. We conclude that while current data are too limited in momentum coverage, future data for higher trigger energy might provide the lever arm in away side hadron momentum necessary to perform medium tomography, provided that sufficient precision can be achieved. 
Thorsten Renk and Kari J. Eskola