The question: How much does elastic energy loss contribute to the jet quenching observed at RHIC? has baffled theorists for some time. Originally, it was thought that elastic energy loss of partons was small, compared with radiative energy loss, but various aspects of the jet quenching data from RHIC led some theorists to reconsider the importance of elastic, i.e. collisional, energy loss:
The manuscript is a contribution to the ongoing debate. It explores the phenomenology of elastic energy loss in back-to-back coincidence measurements of hadrons emitted in nuclear collisions at RHIC. Because the jet opposed to the trigger hadron traverses, on average, a much longer path inside the medium, it is more sensitive to the differences in pathlength dependence of elastic and inelastic energy loss. Elastic energy depends linearly on the path length L, while inelastic energy loss has a quadratic path length dependence. The results presented by the author strongly favor the dominance of inelastic (radiative) energy loss and indicate that any elastic energy loss component must be small.