Hard scattering at RHIC: Experimental review

The most significant results on hard scattering processes in Au+Au, p+p, and d+Au collisions at sqrt(s_NN) = 200 GeV obtained after 3 years of operation at the BNL Relativistic Heavy-Ion Collider (RHIC) are summarized. Hadron production at high transverse momentum (p_T) in central Au+Au collisions shows very different properties (production yields, flavor composition, azimuthal correlations, …) in comparison to p+p, d+Au, and peripheral Au+Au collisions, and this fact constitutes arguably the most interesting outcome of the experimental program so far. Four main topics are covered in this report: (i) the depletion of high p_T inclusive hadron spectra, (ii) the anomalous'' baryon-meson composition at intermediate p_T's, (iii) the disappearance of away-side azimuthal (jet) correlations, and (iv) the large value of collective azimuthal (elliptic flow) correlations. Additionally, the observed high p_T Cronin enhancement’’ in d+Au collisions will be discussed. A succinct comparison of experimental data to theoretical models is also provided.