Master Thesis defense by Mikkel Tornhøj Petersen

Title: Search for a small droplet of Quark-Gluon Plasma with flow-vector fluctuations in p-Pb collisions

Abstract:

Quark-gluon plasma (QGP), a unique state of matter, is created in relativistic heavy-ion collisions, while no direct experimental observation can be made to prove its existence and properties in small collision systems such as proton-lead collisions.

In heavy-ion collisions, the collective expansion of the final state particles is characterized by the anisotropic flow measured through flow vectors. Experimental data show that the flow vector fluctuates event-by-event as a function of the particle kinematics, which originates from the fluctuations in the initial energy density of the nuclear collisions.

In this thesis, both transverse momentum- and pseudorapidity-dependent flow vector fluctuations have been measured in p-Pb collision at the LHC. State-of-the-art non-flow suppression techniques have been used to minimize the potential non-flow contaminations, which is a critical challenge for flow measurements in small system studies. To further improve our understanding of the physics mechanism beyond, comparisons to the calculations from a transport model with the QGP recreation will be presented.

These results will provide tight constraints on the fluctuating initial conditions in small systems, allowing us to explore how anisotropic flow develops from the initial geometry through the dynamic evolution of the created system in p-Pb collisions. They will eventually help to understand the origin of anisotropic flow in small collision systems and answer if a droplet of QGP has been produced in experiments.