Matter is usually comprised of protons and neutrons which consist of quarks bound tightly together by the Strong Interaction of Particle Physics. However at incredibly large temperatures of a few trillion Celsius, quarks become free and a new and poorly understood “Quark-Gluon Plasma” (QGP) phase is created. While the QGP is presumed to have existed soon after the Big Bang, it has also been produced in experiments where heavy nuclei (such as gold) are collided in particle accelerators at virtually the speed of light. This has been performed in the Large Hadron Collider in CERN and at the Brookhaven National Laboratory on Long Island, USA.

Because each nucleus is incredibly small (100 billion of them side-by-side would span a distance of 1mm) the region of QGP created is correspondingly small. Due to this tiny size, it is impossible to place detectors inside this region, and, in any case, they wouldn’t work because they’d instantly melt into the plasma phase! The plasma “fireball” also expands and cools incredibly rapidly, so it quickly returns to the normal state of matter where quarks are tightly bound.

So to understand the QGP, physicists have to rely on observations of particles ejected from the fireball region out into the “normal” phase of matter and into their detectors and then “reverse engineer” the physics of the QGP. To make the connection from the detected particles back to the fireball, it is therefore essential to understand the QGP’s “transport” properties, i.e. how it expands and flows as a bulk material.

One such property is the electrical conductivity, which is what the quantity this project has calculated. This requires supercomputers, such as those provided by the DiRAC Consortium, in order to simulate the many degrees of freedom of the strong Interaction. Our results, shown in the figure, are the first time anyone has calculated the temperature dependency of the conductivity of matter across transition temperature. In this figure, this transition temperature corresponds to around 180 MeV.