Differential Measures of Parton Energy Loss in the Quark Gluon Plasma Using Photon Jet Correlations

Lehigh University, Bethlehem PA

Investigators

Abstract

It is a well-established fact that protons and neutrons are made up of smaller constituents called quarks and gluons. In collisions using two beams of heavy nuclei, a new state of matter is formed, called the quark-gluon plasma (QGP). This project will answer fundamental questions about the QGP, such as how matter is transformed from a collection of protons and neutrons to a free state where quarks and gluons can travel through space unhindered, much like they did in the primordial soup of matter following the Big Bang. The goal of the project is to probe the inner workings of the QGP by resolving its properties at much shorter length scales by using hard collisions of quarks to probe this hot nuclear medium. This research will be performed at the Solenoidal Tracker at the Relativistic Heavy Ion Collider (STAR), which is located at Brookhaven National Laboratory. Particle jets are formed in the very initial stages of the heavy ion collision, when two quarks or gluons have a hard scattering in which they are kicked in opposite directions from one another and roughly perpendicular to beam of heavy ion particles. The quarks and gluons that are kicked out in such an interaction will travel through the medium, interacting and losing energy to it. They then fragment and hadronize into a spray of particles that can be measured by the detectors at STAR. Specifically, the effort will concentrate on observables related to prompt photon-jet correlations at the top energies at RHIC. This has the advantage over other observables that the transverse momentum of the jet is explicitly known due to both conservation of momentum, and the fact that the photon does not interact with the Quark Gluon Plasma. These measures will be necessary to understand the temperature and energy dependence of key features of theoretical models of the quark-gluon interactions.