High-pt suppression and surface effects in nucleus-nucleus collisions

Constantin Loizides

Parton energy loss effects in heavy-ion collisions are discussed within the Parton Quenching Model (PQM), constructed using the BDMPS quenching weights and a Glauber-based description of the collision geometry at mid-rapidity.

The single parameter of the model is adjusted to describe the nuclear modification factor measured in central Au-Au collisions at top RHIC energy. The model is then applied to other high-pt observables, their evolution with centrality, and to describe/predict high-pt suppression effects for other AA colliding systems and centre-of-mass energies.

The inspection of production points and emission angles for primary partons within PQM reveals that in central collisions only those partons which are produced near the surface escape from the medium and contribute to the production of high-pt particles. In the case of back-to-back parton pairs this bias results in the tangential emission of the pair with respect to the surface: predominantly those pairs escape where both partons feel the presence of the medium as little as possible. This situation will be compared to latest findings for gamma-jet correlations.