Dissertation: How to improve our understanding of the interaction between fundamental particles using measurements from the Large Hadron Collider? (ÖԲԱٲ)
Just a millionth of a second after the big bang, our universe was an extremely hot, dense soup of particles, where quarks and gluons roamed free. Today, they exist in bound states as protons and neutrons. To recreate these extreme conditions, heavy-ions like gold or lead nuclei collide, creating a tiny fireball where everything "melts" into a quark-gluon plasma (QGP), which might be the hottest matter in the universe, 250,000 times hotter than the core of the Sun. It cools instantly, leading to the formation of ordinary matter.
How does quark-gluon plasma behave?
By pinning down the value of the transport properties of the QGP, such as shear viscosity, with help from sensitive flow observables in large collision systems, there are more guidelines to go after, when exploring the possibility of QGP being formed in small collision systems. This will give us a better understanding of the matter created in heavy-ion collisions, as well as the early universe and the fundamental aspects of physics.
The ALICE detector at CERN is used to investigate the short-lived QGP. We cannot directly observe it, but instead use information from the final state particles. These particles move towards the detector in collective patterns, a phenomenon referred to as flow.
“The primary goal of my research is to examine the behavior of the quark-gluon plasma (QGP) throughout heavy-ion collisions using flow observables. This involves experimental measurements and Bayesian analysis. The focus lies on understanding the transport properties of the QGP, especially the specific shear viscosity (η/s), which is a physical quantity denoting how a fluid deforms under shear stress, explains Anna ÖԲԱٲfrom Ģֱ.
A significant step to understanding of the QGP
The QGP, first observed in heavy-ion collisions over 20 years ago, is a unique state of matter that continues to be the subject of ongoing research. A main area of study is its transport properties, especially its specific shear viscosity (η/s). This property measures a fluid's resistance to deformation - a higher η/s indicates greater resistance, similar to the high viscosity of honey compared to water. A lower η/s value signifies a near-perfect fluid with minimal internal friction. The QGP's η/s is believed to be notably low, indicating an exceptionally fluid state.
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Through experimentally measured higher-order harmonic flow observables and model predictions, we have managed to significantly reduce the uncertainty of the η/s, bringing us closer to determining its actual value. These findings represent a significant step forward in our understanding of the QGP, says ÖԲԱٲ.
Practical applications of research findings
Additionally, we are exploring the possibility of QGP formation in smaller collision systems, such as proton-proton collisions, a theory that challenges previous beliefs that QGP could only be formed in heavy-ion collisions. As part of this investigation, we are using new methods that eliminate all background noise, and we continue to observe a flow-like signal in these smaller systems.
This research is not only vital for advancing our understanding of the universe, but it also has practical implications. The insights gained can potentially lead to technological innovations, foster international collaboration, and find applications in diverse fields like medicine and nuclear energy, contributing to societal progress and economic development.
M.Sc. Anna ÖԲԱٲ defends her doctoral dissertation “Improving understanding of the QCD matter properties with flow harmonic observables at the LHC” on 19.6.2024 at 12:00. Opponent is Professor Anne Sickles (University of Illinois at Urbana Champaign, USA) and custos is Senior Lecturer Dong Jo Kim (Ģֱ). The language of the dissertation is English.
The dissertation “Improving understanding of the QCD matter properties with flow harmonic observables at the LHC” can be read on the JYX publication archive: