Advances in High Energy Nuclear Physics

Among the four fundamental forces in nature the strong nuclear force is understood the least. The strong force is behind many important processes in the universe. One particularly important aspect of the strong nuclear force is the existence of quark gluon plasma.

If ordinary matter is heated up to temperatures of about 1,000,000,000,000 degrees, hotter than the core of the sun, atoms and molecules cease to exist and even protons and neutrons inside atomic nuclei melt. The remaining primordial soup of quarks and gluons is what filled the very early universe. One can recreate quark gluon plasma in large particle colliders by smashing heavy nuclei into each other.

Experimental programs at the Large Hadron Collider in Europe and the Relativistic Heavy Ion Collider in the US study quark gluon plasma. The PI and his group will carry out research that will improve our understanding of properties of quark gluon plasma in nuclear collisions. The project will use computer simulations, machine learning, and advanced statistical methods to reach this goal. It will provide training for graduate students and young scientists in nuclear science.

Quark gluon plasma in nuclear collisions is studied through the use of probes that are created together with the plasma in these collisions. Among the most promising probes are high energy photons and jets. Photons have the unique property that the quark gluon plasma is almost transparent to them.

They can thus deliver information from deep inside the droplet of plasma that is created. However, state-of-the-art calculations assume that the plasma is actually perfectly transparent to photons. This project attempts to quantify the errors that are made with the assumption of a complete absence of final state interactions.

This can lead to a better understanding of available data on photons which exhibits some puzzling features. Jets are seen in detectors as collimated sprays of hadrons, i.e. bound states of quarks and gluons. They emerge from a single, very energetic quark or gluon that has been scattered away from the axis of the colliding beams.

Jets evolve in a complicated pattern in space-time as well as momentum space while they interact with the plasma around them. This project will try to go beyond the simple space-time picture, inspired by classical propagation, that is often utilized in the interpretation of data, by looking at the equivalent of Wigner distributions for these jet showers.

Lastly, the PI will continue to develop and explore the "Hybrid Hadronization" computer code. Hybrid Hadronization is a novel simulation of the process of quarks and gluons forming hadrons in the last phase of nuclear collisions. Applications will focus on jets and involve the recombination of quarks and gluons from the plasma with those in jets.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.