Welcome to the Symposium on Contemporary QCD Physics and Relativistic Nuclear Collisions, to be held at the Central China Normal University (CCNU) during November 9~11, 2019. This event is hosted by the College of Physics at CCNU and the meeting venue is Room 409 of Building #9. November 9th will be registration day and scientific talks will be presented on 10th and 11th. The symposium banquet will be in the evening of November 10th. 

More than forty years past its advent, Quantum Chromodynamics (QCD) as the fundamental theory of strong interactions, continues to intrigue physicists worldwide with broad inquiries. Over the two decade into the 21st century, contemporary QCD physics witnesses unprecedented advances with many fascinating discoveries and develops into a vibrant area of research with multiple thriving scientific frontiers. 

A central theme of QCD physics has focused on the theoretical understanding of strongly interacting matter under a variety of extreme conditions as well as their experimental manifestation in hadronic and nuclear collisions. Prime examples of such extreme matter include e.g. the quark-gluon plasma (QGP), the Color Glass Condensate (CGC) and the Glasma. 

The study of QCD at super high energy, via imaging internal parton structures of hadrons and nuclei from HERA to RHIC and LHC, have seen tantalizing evidences for the seminal idea that a new form of matter — the Color Glass Condensate (CGC) arises in this regime. A future Electron Ion Collider (EIC) facility may soon be on the horizon and will be able to fully investigate the realm of CGC. 

The phase of QCD matter at primordially hot temperatures is known as a quark-gluon plasma (QGP), with its early conception dating back to a number of pathbreaking papers from mid to late 1970s. It was soon envisioned to create QGP in laboratories by colliding relativistically moving large nuclei, with pioneering ideas like hydrodynamic evolution, jet energy loss, electromagnetic emissions, pion interferometry, etc, that emerged around early 1980s  and led to the start of heavy ion collision physics program over the next several decades. The QGP has been discovered and is now routinely created by high energy nuclear collisions at the RHIC and the LHC. Detailed measurements along with sophisticated transport and hydrodynamic modelings have found the QGP to be the most perfect quantum fluid — a surprising property yet with early hint already from mid 1980s. The novel phenomenon of jet quenching has served as an indispensable and powerful tool for characterizing the properties of QGP, with its theoretical frameworks being developed since 1990s and evolving toward maturity and with continuously growing experimental efforts. 

Between the initial CGC and the formation of the QGP perfect fluid, there emerges another novel state of QCD matter, proposed in mid 2000s and named as the Glasma, which provides a unique test bed for understanding non-Abelian gauge theories in the far-from-equilibrium regime. Studies of the Glasma have led to unusual insights such as transient Bose-Einstein condensation, non-thermal fixed point or emerging hydrodynamic behaviors without thermal equilibrium and may also bear importance for particle production in small colliding systems.

Theoretical investigation of QCD thermodynamics at very high temperatures has been significantly advanced through systematic developments of effective field theory framework like the hard thermal loops. With the help of modern super computing power, lattice QCD simulations have provided the first-principle answer to QCD thermodynamics (at zero baryon density) across all temperature range and fully quantified the nature of the transition from hadronic phase to quark-gluon phase, achieving the goal of a long pursuit starting from early papers in late 1970s to early 1980s. Today’s lattice QCD has become a major thrust of QCD research in all aspects, unraveling many mysteries hiding behind the QCD nonperturbative dynamics. 

Exploration of QCD matter at extremely baryon-rich regions, whiles so far approachable with lattice QCD only via susceptibilities near zero chemical potential, has  been strongly boosted by recent astrophysical observations, especially by the maximal mass of neutron stars and by the exciting discovery of gravitational waves from neutron start mergers. The exact structures of QCD matter at a few times of nuclear saturation density and beyond still remains a challenge and presents opportunities, with interesting ideas such as the quarkyonic phase. Experiment-wise, the Beam Energy Scan (BES) program at RHIC as well as a number of future low energy collider like FAIR, NICA and HIAF  will soon provide fresh information for probing QCD properties in the baryon-rich region. 

The purpose of this Symposium is to reflect on the past history, examine the present status and discuss the future directions of these exciting research frontiers. 

This Symposium also celebrates the exceptional scientific accomplishments of three distinguished colleagues: J.-P. Blaizot, M. Gyulassy, and L. D. McLerran, who turned 70 this year. Their careers of generating seminal and impactful ideas have concurred with the QCD era of nuclear physics from its early days into its present modern state. Their outstanding contributions have helped shape a large part of the contemporary QCD physics and relativistic nuclear collisions.