104 Chapter 4: Fluctuations in Jet Tomography What is most striking in Fig. 4.4 is the hierarchy of Q -dependent length scales. No single, representative path length can account for the distribution of all flavors. In general heavier flavors are less biased toward the surface (in direction φ ) than lighter flavors since the energy loss decreases with the parton mass. Gluons are more surface biased than light quarks due to their color Casimir enhanced energy loss. In addition, note the surprising reversal of the u and c suppressions, also seen in Fig. 4.5. Fig. 4.2 shows that the energy loss of c is somewhat less than for u ; however, the higher p$_{T}$ power index, n , of c relative to u – as predicted by pQCD and due to the valence component of u – compensates by amplifying its quenching. However, it is clear that none of the distributions can be usefully cate- gorized as surface emission. The characteristic widths of these distributions range from Δ x ≈ 3 − 6 fm. Such a large dynamic range of path length fluc- tuations allows for the consistency of simultaneously reproducing both the electron and pion data. We turn next to Figs. 4.6 and 4.7 to show the interplay between dynamical geometry seen in Fig. 4.4 and the elastic-enhanced quenching of partons. In Figs. 4.6 and 4.7 the solid green curves labeled “DGLV+TG/BT: Full Geom- etry” are the results using approach I based on Eq. (4.4). The curves labeled TG and BT are from approach II based on Eq. (4.7). The effective fixed L$_{Q}$ in II were taken to match approximately the green curves in which full path length fluctuations are taken into account. This procedure is not exact be- cause of the different numerical approximations involved, but the trends are