High pT suppression: path-length dependence

• 2 times more suppression out-of-plane (“long” direction)
• than in-plane (“short” direction).
• Glauber parton energy loss model predicts only ~50% increased “out-of-plane” vs “in-plane” π0 emission
• Azimuthal anisotropy stronger than “canonical” L2 (or L) path-length dependence.
• Source of extra azim. anisotropy above pT ~ 4 GeV/c ?