From Professor Steffen Bass: In an article just published in the Physical Review Letters, a group of theorists including Prof. Steffen A. Bass showed that the quark-gluon plasma (QGP) created in high energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and the Large Hadron Collider (LHC) at CERN forms the most perfect liquid ever studied in the laboratory. To read more about this article, click here:
Using a new theoretical tool developed by Dr. Huichao Song at Ohio State in collaboration with Prof. Bass and other colleagues at OSU and the University of Tokyo, the dynamical evolution code VISHNU, the researchers were able to extract from an analysis of experimental data a tight upper limit for the QGP shear viscosity. The reported work improved a previously established upper limit by about a factor three and established that QGP is even more liquid than a gas of ultracold Lithium atoms in the unitary limit of infinitely large scattering length. The quantum mechanical uncertainty principle predicts for any real fluid an absolute lower limit for the specific shear viscosity (i.e. the unitless ratio of shear viscosity to entropy density, η/s) of around 1/(4π)=0.08. The upper limit for the QGP established in the reported work is less than 2.5 times this theoretical lower bound; a similar analysis by Prof. John Thomas' group here at Duke for ultracold lithium atoms gives values around 3-4 times this lower bound. It is a curious observation that the quark-gluon plasma holds at the same time the record for having by far the largest absolute value of shear viscosity (in standard dimensionfull units) and by a significant margin the smallest specific shear viscosity (in dimensionless units). It is the latter that controls the fluidity of the QGP -- hence the label "nearly perfect liquid" that the researchers attach in their paper to the quark-gluon plasma. Read the article here.