Alice Ohlson

A strongly-coupled, deconfined state of quarks and gluons, known as the Quark-Gluon Plasma (QGP), is created in high-energy collisions of heavy nuclei. The QGP can be probed by high-momentum quarks and gluons (collectively known as partons) that are produced in hard scatterings early in the collision. The partons traverse the QGP and fragment into collimated “jets” of hadrons. Studies of parton energy loss within the QGP, or medium-induced jet quenching, can lead to insights into the interactions between a colored probe (a parton) and the colored medium (the QGP).

Two analyses of jet quenching in relativistic heavy ion collisions are presented here. In the jet-hadron analysis, it is shown that jets that traverse the QGP are softer (consisting of fewer high-momentum fragments and more low-momentum constituents) than jets in p+p collisions. There are also indications that the shapes of the distributions of charged hadrons about the jet axis are modified by interactions with the QGP. Additionally, a measurement of jet v2 demonstrates that the parton energy loss depends on the length of the parton’s path through the QGP. The data analyzed here were collected in sqrt(s_NN) = 200 GeV Au+Au and p+p collisions at the STAR detector at the Relativistic Heavy Ion Collider.