Hard probes observables (foreword)

• Early production (t~1/pT~ 0.1 fm/c) in parton-parton scatterings with large Q2

• Direct probes of partonic phases Þ Sensitive to hot/dense medium (QGP) effects: parton energy loss, color screening ...

• 3 types: High-pT particles (jets, prompt g), large mass (D, B, J/Y) particles, [Elliptic flow]

• Comparison to available set of baseline "vacuum" data (pp Ö AA) via Ncoll (# of binary inelastic colls.) scaling:

• Elementary processes calculable via pQCD.

• Factorization theorem: