Inconsistencies in, and short pathlength correction to, RAA(pT) in A+A and p+A collisions

We present the first leading hadron suppression predictions in Pb + Pb and p + Pb collisions from a convolved radiative and collisional energy loss model in which partons propagate through a realistic background and in which the radiative energy loss receives a short pathlength correction. We find that the short pathlength correction is small for D and B meson R AA ( p T ) in both Pb + Pb and p + Pb collisions. However the short pathlength correction leads to a surprisingly large reduction in suppression for π mesons in p + Pb and even Pb + Pb collisions. We systematically check the consistency of the assumptions used in the radiative energy loss derivation-such as collinearity, softness, and large formation time-with the final numerical model. While collinearity and softness are self-consistently satisfied in the final numerics, we find that the large formation time approximation breaks down at modest to high momenta p T ≳ 30 GeV . We find that both the size of the small pathlength correction to R AA ( p T ) and the p T at which the large formation time assumption breaks down are acutely sensitive to the chosen distribution of scattering centers in the plasma.