CAREER: Jet Measurements and a Novel Hadronic Calorimeter at the Relativistic Heavy Ion Collider

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This award supports the PI and her research group in investigations to understand the strong nuclear force and to engage with middle and high school students in the Atlanta area to broaden their understanding of nuclear physics. Quarks and gluons are the most fundamental building blocks of normal matter. However, due to the nuclear strong force, they cannot be observed individually and are confined within particles like protons and neutrons in the nucleus. Under extreme temperatures and densities, a new state of matter known as the quark-gluon plasma (QGP) can be formed. The QGP is an excellent test bed for the theory of the strong force. The Relativistic Heavy Ion Collider (RHIC) is one of two facilities world-wide capable of creating the QGP. In addition to producing the QGP, heavy ion collisions produce energetic quarks and gluons that interact with the QGP and then produce a spray of particles called a "jet" that can be measured with detectors. While previous RHIC experiments have shown evidence of jet energy loss, a new experiment called sPHENIX will enable precise measurements of fully reconstructed jets. sPHENIX includes a special detector, the first central hadronic calorimeter (HCal) at RHIC, which is essential for measuring the energy of these jets. In addition to jet related analyses, this award includes testing HCal components with cosmic rays before assembly and development of a calibration procedure for this novel detector.Working with the sPHENIX HCal will provide opportunities for the diverse population of undergraduates at GSU to gain experience in research and hardware. The undergraduate and graduate students involved in this project will be trained to work in big data analysis, network within large collaborations and develop useful hardware skills that are all important for preparing the next generation in a variety of STEM fields. Using components similar to those for the sPHENIX HCal, GSU students will work with Atlanta area middle and high school students to measure cosmic rays. Participation of the GSU Women in Physics student organization, for which the PI is the advisor, allows the middle and high school students to engage in science and work with a diverse group of scientists at a critical time when students are choosing career paths and is intended to help encourage a diverse population to pursue STEM careers. The sPHENIX hadronic calorimeter has a novel tilted plate design, which includes scintillator tiles embedded between steel plates. This award includes the development of a calibration procedure for this novel detector, which will be essential for successful measurements. Testing the scintillator tiles with cosmic rays will provide baseline calibration information and experience from the beam test prototype will be useful in developing the calibration procedure, which ultimately may include using photon tagged jets in p+p collisions to set the jet energy scale. Photon tagged jets are also important probes of the QGP. Since the photon is unmodified by the QGP, the photon's energy provides access to the initial parton energy of the opposing jet and therefore access to how much energy was lost. In parallel to sPHENIX preparations, this project will make the most precise photon tagged correlation measurements achievable from the 16 years of PHENIX data. These correlation measurements access the transport coefficient, q-hat, which measures the energy loss of partons per unit pathlength. Jet structure measurements give further insight to the fragmentation and energy loss of the partons in the medium. sPHENIX will enable new jet observables at RHIC that will advance our understanding of energy loss mechanisms in the QGP and thereby further our understanding of QCD under extreme conditions.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.