Exploring the Phase Diagram of QCD Matter

02/12/2021 - 3:30pm to 4:30pm
Speaker(s) / Presenter(s): 
Daniel Cebra (UC Davis)

Host: Fatemi


Collisions between relativistic heavy-ions (gold or lead) are  energetic enough to vaporize the
participating neutrons and protons  creating an equilibrated plasma of quarks and gluons. This
plasma is thought to be similar to the state of the universe about one microsecond after the big bang.
The existence of this deconfined partonic phase has been well established an the top energies
available at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). However,
this plasma is a complicated phase of matter; the nature of the force between objects
operating under the color force is quite different from those  interacting through the electromagnetic
force, which has driven our understanding of what it means to be 'matter' or to be a 'phase of matter'.
Although we had made progress in understanding the nature of hot dense nuclear matter, there were still
important open questions about how the matter undergoes the transition between a quark-gluon plasma and
a hot hadronic gas. If the plasma has an equal mix of quarks and anti-quarks, lattice QCD calculations
now tell us that  there will be a crossover transition. However, in heavy-ion collisions, we create
systems with an excess of quarks, and under these circumstances we expect a first order phase transition,
the termination will be a critical point. In 2010 and 2011, RHIC performed a scan of several beam energies
in order to map the QCD matter phase diagram. Results of that can suggested that the critical point could
be at the lowest energy feasible to be run at RHIC, therefore in the follow-up beam energy scan (BES-II),
which is currrently being run (2018-2021), we have added a fixed-target energy scan to access lower energies and
higher ratios of quarks to anti-quarks. This talk will report on the conclusions that can be drawn
from these energies scan concerning the phase diagram of QCD matter.



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