Using Jets as a Probe of the Quark Gluon Plasma

Lehigh University, Bethlehem PA

Investigators

Abstract

The building blocks of matter, protons and neutrons, are made up of smaller constituents, which are called quarks and gluons. In collisions of heavy nuclei accelerated to nearly the speed of light, a new state of matter is formed, called the quark-gluon plasma (QGP). In this matter, the protons and neutrons seem to "melt", allowing the quarks and gluons to form a soup-like phase with a viscosity that is nearly as low as possible, earning it the title of a perfect liquid. This project will answer fundamental questions about the QGP, such as how normal matter came into being and how it evolved from the primordial soup of matter which existed just after the Big Bang. The goal of the project is to probe the inner workings of the QGP and determine its properties at much shorter length scales by using high momentum collisions of quarks from within the heavy nuclei collisions. This research will be performed with the STAR detector at the Relativistic Heavy Ion Collider (RHIC), which is located at Brookhaven National Laboratory. This award will also support the PI's mentoring of graduate students and undergraduate students as well as broadening the participation of people from underrepresented groups in STEM through outreach activities. Particle jets are formed in the very initial stages of the heavy nuclei collision, when two quarks or gluons have a high momentum collision. In this collision they are kicked in opposite directions from one another, roughly perpendicular to the beam of heavy ion particles. The quarks and gluons from such an interaction will travel through the QGP, interacting with and losing energy to it. They then fragment and hadronize into a spray of particles which can be measured by the detectors at STAR. The energy scale of the particle jet is inversely proportional to the length scale that it can probe. This effort will focus on observables related to prompt photon-jet correlations at the top collision energies at RHIC. Observables in this category have the advantage that the transverse momentum of jets produced these collisions is explicitly known, due to both conservation of momentum, and the non-interaction of the photon with the QGP. These measurements will be necessary to understand the temperature and energy dependence of key features of theoretical models of the quark-gluon interactions, and thus understand how the strong nuclear force operates. 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.