  The basic idea of jet tomography is to infer information about the density
evolution of the medium created in heavy-ion (A-A) collisions by studying the
suppression of hard probes in an A-A environment as compared to the baseline
process known from p-p collisions. The suppression of back-to-back correlations
in heavy-ion collisions allows, due to a different geometrical bias, a view
into the medium which is qualitatively different from the one offered by single
hadron suppression. A control parameter for the suppression corresponding to a
systematic variation of in-medium pathlengths and density can be obtained by
studying collisions at finite impact parameter b. A systematic variation of
pathlength can then be introduced by studying the suppression pattern as a
function of the angle phi with the reaction plane. Using a 3-d hydrodynamical
evolution model for the medium and a Monte-Carlo model which has been shown to
successfully reproduce the measured suppression of back-to-back correlations in
central collisions of Au-Au at 200 AGeV, we compute the suppression as a
function of phi for b of 2.4 fm. 4.5 fm, 6.3 fm and 7.5 fm. Given that this
involves variations in both control parameters b and phi a comparison with data
should eventually allow to place strong constraints on the combination of
energy loss model and medium evolution model.
