RUI: Investigation of Heavy Quark Energy Loss in Relativistic Nucleus-Nucleus Collisions at the CERN 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. The strength of this energy loss is directly related to the density of the quark gluon plasma and varies according to the type of parton. From observations at RHIC, the heavier quarks appear to be more strongly coupled to the quark gluon plasma than was previously expected. High energy electrons are produced by the decays of particles made from heavy quarks, so their presence within the cluster of particles that comprise an observed jet is strong evidence for the jet to have originated from a heavy quark. The energy loss of these electron-jets can be used to investigate the properties of the quark gluon plasma. 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 the energy loss of heavy quark jets as a probe. 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.