Jetography in Heavy Ion Collisions

During the last decades, heavy ion collisions have become an increasingly active area of research. This system provides a unique laboratory to study partonic matter (quarks and gluons, the nucleon constituents described by Quantum Chromodynamics) at temperatures and densities much higher than those inside a nucleus. Under such extreme conditions partons reach deconfinement, forming a new phase of matter known as the quark-gluon plasma. This dense nuclear medium has become an important object of study due to exhibiting collective behaviour, and because it is thought to have filled the universe in the instants after the Big Bang.

Owing to its high temperature the quark-gluon plasma is very short-lived, making it impossible to observe directly. It can instead be studied indirectly through the high energy particles produced during the collision, typically observed as narrow jets. As these jets develop, the medium’s evolution becomes imprinted in their kinematic information. By comparing heavy-ion measurements with unmodified jet samples from proton-proton collisions, the medium properties can be extracted and studied.

The work developed in this thesis is aimed at extending the present understanding of jet modifications due to the quark-gluon plasma. The first part of this work focuses on gluon radiation from a pair of partons traversing a deconfined medium. By casting the gluon radiation spectrum in terms of solutions to integral equations which can be solved numerically, it could be computed without the usual assumptions about the nature of parton-medium interactions.

The second part of this work examines the interplay between jet development and medium evolution. Three equivalent parton shower algorithms were constructed, each generating radiation inside a jet according to a different ordering pre scription. When simplified medium model is applied to each jet sample, the fraction of quenched jets was found to be sensitive to the ordering prescription