Hard Probes in Heavy-Ion Physics

Understand

The aim of ultrarelativistic heavy ion physics is to study collectivity and thermodynamics of Quantum Chromodynamics (QCD) by creating a transient small volume of matter with extreme density and temperature.

• There is experimental evidence that most of the particles created in such a collision form indeed a thermalized system characterized by collective response to pressure gradients.
• However, a numerically small subset of high transverse momentum ($P_T$) processes takes place independent of the bulk, with the outgoing partons subsequently propagating through the bulk medium.
• Understanding the modification of such 'hard probes' by the bulk medium is an important part of the efforts to determine the properties of hot and dense QCD matter.