RUI: Jet Tomography of Compressed Nuclear Matter with the ALICE Experiment at the LHC

California Polytechnic State University Foundation, San Luis Obispo CA

Investigators

Abstract

Shortly after the Big Bang, the Universe was composed of a plasma of free particles called quarks and gluons. As the Universe expanded and cooled, the quarks and gluons condensed into the protons and neutrons which now make up the cores of all atoms. This phase transition from a hot, dense plasma to a gas of normal matter is similar to that of steam condensing into liquid water. Using large particle accelerators, scientists are recreating this subatomic soup in the laboratory by colliding gold or lead atoms at very high energies and studying the intriguing properties of this unusual state of matter. One of the most important discoveries to come from experiments at the Relativistic Heavy Ion Collider (RHIC) is that the dense matter is opaque to very high energy quarks and gluons produced in the collisions. These `partons' suffer tremendous energy loss as they make their way out of the collision zone, depositing a large fraction of their initial energy in the medium. As a result, far fewer of these partons than expected escape to fragment into jets of high energy particles while those in the wake of the speeding parton pick up some additional energy. The subtle changes in the distribution of energy to particles coming from the collision can be detected and studied in a manner analogous to how X-ray images show variations in the density of bones and organs within the human body. For this reason, the technique is known as jet tomography. A surprising conclusion from evidence collected so far is that the matter produced at RHIC, which was initially expected to behave like a gas, actually exhibits properties more like a liquid. The CERN Large Hadron Collider (LHC) in Switzerland will collide nuclei at energies 30 times higher than at RHIC, producing an even hotter, denser, longer-lived medium. This RUI project will utilize the ALICE experiment to explore the properties of this matter using jet tomography. Undergraduate students working on this experiment will be trained in the most advanced data collection, reduction and analysis techniques at the cutting edge of high energy nuclear physics. They will be able to apply these skills in a wide variety of careers, whether they choose to pursue an advanced degree in basic science or not. Their contributions will also help us develop new insights into the fundamental interactions among the basic building blocks of the universe, leading to a deeper understanding of the world around us.