Lijuan Ruan: Then and Now / 2013 Early Career Award Winner

WHAT DID THE 2013 EARLY CAREER AWARD ALLOW YOU TO DO?

My research uses heavy-ion collisions to study the “quark-gluon plasma” (QGP) and the phase diagram of Quantum Chromodynamics (the study of the strong interactions between quarks mediated by gluons).

QGP is believed to have existed just microseconds after the Big Bang. At that time, there were no protons and neutrons, just a sea of quarks and gluons—the building blocks of atomic nuclei. 

Scientists recreate this quark-gluon plasma by accelerating heavy ions to nearly the speed of light and smashing them together at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). 

Studies of this hot quark soup are revealing intriguing surprises and insights into the nature of the early universe and the strong force. Would the strong force between a quark and an anti-quark be modified in the QGP, and if so, how?

The Early Career Award enabled me to collaborate with several outstanding postdoctoral researchers. During this time, we conducted measurements on the melting of various quarkonium states. These are bound states composed of a heavy quark and anti-heavy quark held together by gluons with differing binding energies. One of these quarkonium states is called Upsilon. It’s made of a bottom quark and the bottom quark’s antiparticle partner.

This research utilized the newly installed Muon Telescope Detector at the Solenoidal Tracker at RHIC. 

We published the measurement of how much the three Upsilons are suppressed individually at RHIC. The outcomes matched what theory predicted. The Upsilon that’s less tightly bound is notably more suppressed compared to the one that’s tightly bound. This finding provides evidence for models that incorporate modifications to the strong force between a quark and an antiquark in the hot, dense medium of the QGP. 

The Early Career Award helped me build a team to work together. I learned tremendously from each of my team; quite a few have become staff members at national labs or faculty at universities. They are thriving and becoming leaders in the field. It is satisfying to see them shine.

ABOUT: 

Lijuan Ruan is a Senior Physicist in the Physics Department at Brookhaven National Laboratory

SUPPORTING THE DOE SC MISSION:

The Early Career Research Program provides financial support that is foundational to early career investigators, enabling them to define and direct independent research in areas important to DOE missions. The development of outstanding scientists and research leaders is of paramount importance to the Department of Energy Office of Science. By investing in the next generation of researchers, the Office of Science champions lifelong careers in discovery science. 

For more information, please go to the Early Career Research Program page.

THE 2013 PROJECT ABSTRACT: 

Title – Mid‐rapidity Di‐lepton Measurements at RHIC with the Muon Telescope Detector at STAR

An important task in today’s relativistic heavy ion physics is to study the fundamental properties of the Quark Gluon Plasma (QGP), including the temperature, density profile, and color screening. 

Data taken over the last decade have demonstrated that the Relativistic Heavy Ion Collider (RHIC) has created the QGP, a hot, dense medium with partonic degrees of freedom. However, the initial temperature of the QGP is not well constrained by previous experimental results and estimates dependent on models have large uncertainties. The planned study will measure the decay of different quarkonium states into two muons. These bound states of two heavy quarks are predicted to melt before decaying at very different temperatures in the QGP. The dissociation of the states depends on the color screening length of the QGP and quarkonium binding energies, that is, how strongly the different colored quarks are screened from each other in the QGP. 

In addition, measurements of muon‐electron correlations from heavy flavor decay will help remove the dominant background for an alternative method of determining the QGP temperature based on the measurement of thermal radiation. With these new techniques, the planned measurements will provide direct information on the temperature and the characteristics of the color screening in the QGP created at RHIC.

RESOURCES:

BE Aboona et al. (STAR Collaboration), “Measurement of Sequential Upsilon Suppression in Au+Au collisions at √sNN = 200 GeV with the STAR Experiment.” Phys. Rev. Lett.130, 112301 (2023). [DOI: 10.1103/PhysRevLett.130.112301]

J Adam et al. (STAR Collaboration), “Measurement of inclusive J/ψ suppression in Au+Au collisions at √sNN = 200 GeV through the dimuon channel at STAR.” Phys. Lett. B 797, 134917 (2019). [DOI: 10.1016/j.physletb.2019.134917]

 

DOE Explains… offers straightforward explanations of key words and concepts in fundamental science. It also describes how these concepts apply to the work that the Department of Energy’s Office of Science conducts as it helps the United States excel in research across the scientific spectrum. For more information on quarks and gluons and DOE’s research in this area, please go to the “DOE Explains…Quarks and Gluons” webpage.     

Additional profiles of the Early Career Research Program award recipients can be found at the Early Career Program highlights page. 

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