Difficulty of extracting energy loss probability distributions from RAA

The nuclear suppression of high transverse momentum P-T hadrons is one of the most striking findings in heavy-ion collision experiments. It has long been recognized that the suppression can be theoretically described by folding the primary parton spectrum with an energy loss probability distribution which is suitably averaged over the collision geometry. However, an interesting problem is to what degree the procedure can be inverted, i.e., given a measurement of the suppression factor R-AA with arbitrary precision, can the probability distribution of energy loss be extracted in a model-independent way? In this Brief Report, we present a conceptual study of the inversion problem for LHC energies and demonstrate that a measurement of R-AA alone is insufficient to determine the distribution, other observables such as gamma-hadron correlations must be taken into account.