16 LEHIGH UNIVERSITY | COLLEGE OF ARTS & SCIENCES SPOT LIGHT FOR A MOMENT after the Big Bang, just a few millionths of a second, the universe was filled with an incredibly hot, dense liquid composed of particles moving at near-light speed. This mixture was dominated by quarks—fundamental bits of matter—and by gluons, carriers of the force that normally “glues” quarks together into familiar protons and neutrons and other particles. A quark-gluon plasma (QGP) occurs when the temperature is so high—an average of 4 trillion degrees Celsius—that individual protons and neutrons comprising atoms melt, and this event is the focus of research by high energy physicist Rosi Reed. Funded by the National Science Foundation’s Major Research Instrumentation program, Reed’s research explores hardware development and data analysis. Working at the Relativistic Heavy Ion Collider (RHIC), which is located at Brookhaven National Labs (BNL) on Long Island, New York, she has been involved in the development of two different detectors— the Event Plane Detector (EPD) for STAR and the sPHENIX Event Plane Detector (sEPD). She uses particle jets as probes to analyze QGP to answer fundamental questions about the nature of quark-gluon interactions. Particle jets are formed when a high momentum quark or gluon splits into a column of particles, which create subatomic particles called hadrons and are measured by the detectors. When this particle travels through the QGP, it will lose energy to the medium in a process called jet quenching. The modification of the jets due to the medium depends on the details of the medium such as its temperature, the size of the fluctuations within it, and the geometry of the QGP droplet. Comparing models and data from proton-proton collisions, the properties of the quark-gluon interaction can be understood. Previously, Reed installed a detector in the STAR experiment to measure charge particle distributions. This past spring, a detector was installed at sPHENIX, which is a massive cylindrical detector wrapped around a beam. Reed’s detector was attached along either end, and it is segmented so that scientists can examine the charged particle distributions. When a collision happens in the detector, Reed and her colleagues want to know the details of how the ions collided. When scientists smash together these ions, a tiny drop of matter forms so hot that the protons and neutrons melt. It’s like quark gluon soup, Reed says. And one of the questions is how do quarks and gluons interact with that soup? One of the main questions of sPHENIX is how a quark or gluon interacts with this quark gluon soup. Reed’s detector allows scientists to understand precisely how hard these ions have struck each other, whether they hit each other head-on or peripherally and what the angle is. ■ Quark Gluon Soup When scientists smash together these ions, a tiny drop of matter forms so hot that the protons and neutrons melt. It’s like quark gluon soup. Part of the sPHENIX detector, the Time Projection Chamber allows nuclear physicists to measure the momentum of charged particles streaming from collisions produced in Brookhaven Lab’s Relativistic Heavy Ion Collider Courtesy of Brookhaven National Laboratory
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