Nearly Perfect Quark-Gluon Droplet at the Smallest Scales
ABSTRACT :
In high energy collisions of large, heavy nuclei (e.g., Au or Pb), a new state of matter consisting of liberated quarks and gluons is formed at a temperature of a few trillion Kelvins. This "Quark-Gluon Plasma" (QGP), discovered at the Relativistic Heavy Ion Collider (BNL) and the Large Hadron Collider (CERN, Switzerland), is found to exhibit amazing collective behavior as a nearly "perfect" fluid, which flows with close-to-zero viscous dissipation. It was thought that elementary collision systems like proton-proton (pp) or proton-nucleus (pA) are too small and dilute to form a QGP fluid so they were often treated as a reference in understanding the emergence of perfect fluidity in large heavy ion systems. Surprisingly, in recent years, evidence for collective effects and QGP formation has also been revealed in those smallest collisions, when looking at a fraction of rare events releasing the largest number of particles. In this talk, I will describe key findings related to the possible formation of the tiniest QGP fluid in pp and pA systems, and discuss their implications to the standard paradigm of heavy ion physics, as well as new opportunities opened up in studying emergent Quantum Chromodynamics phenomena under extreme conditions.
ABOUT THE SPEAKER:
Prof. Wei Li received his Ph.D. in experimental particle and nuclear physics at MIT in 2009. Following a postdoc position at MIT working on the first relativistic heavy ion physics program at the LHC, he joined the Rice faculty in 2012. Prof. Li's interest focuses on understanding emergent behaviors in strong nuclear forces under extreme conditions. Prof. Li has been a leader of the CMS heavy ion program since its inception, serving as co-convener of the group and also the project director of time-of-flight upgrades for heavy ions at the future high-luminosity LHC. His group led a surprising discovery of quark-gluon plasma in proton-proton and proton-nucleus collisions. Prof. Li received an Early Career Award from the U.S. Department of Energy, a Sloan Research Fellowship and a Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House.