Wednesday, September 09, 2015

Particle collider creates ‘primordial goo’ of the early universe


A quark-gluon plasma is the original state of the universe. After the Big Bang, for a length of time extending for perhaps a few milliseconds, matter was so unimaginably super-heated that it was in its most disordered possible state. This means that there was nothing larger or more organized than single subatomic particles — the constituents of relatively enormous things like protons.

The behaviour of this plasma, and the process by which it cooled to form matter as we know it, is one of the most important questions for early universe cosmology today. That’s why it’s so surprising that an American particle collider called the Relativistic Heavy Ion Collider (RHIC) was able to create it with very little actual mass. Their results are published in the journal Physical Review Letters.

As you might imagine, blasting apart matter so violently that even hadrons can’t form takes a lot of input energy. In general, it’s been assumed that any particle collider looking to create a sample of quark-gluon plasma would have to smash together very heavy atomic nuclei. The Large Hadron Collider, and the RHIC itself, have both created quark-gluon plasmas in the past, by making incredibly violent collisions between heavy atoms like lead or gold.

What this particular RHIC experiment did was to create a quark-gluon plasma by colliding a the nucleus of a helium-3 atom  with an atom of gold, which was not previously thought to be possible. The pockets of plasma born of these collisions are much smaller than those created by heavier atoms, but they hung around long enough for scientists to measure their properties. The experiment proved that they are indeed in a state called a “perfect fluid,” in which matter has no internal friction at all, and conducts no heat. This is mostly a tool for physicists in their thought experiments; in the vast majority of real-world cases, a perfect fluid is totally impossible.

But the Big Bang is thought to have put all the matter in the universe into this state, all that once.

A helium-3 nucleus is made of two protons (thus, making it helium) and a neutron, making it one neutron lighter than the most common helium isotope on Earth. This three-particle nucleus was chosen because it is one particle heavier than a two-particle deuterium atom, which the Large Hadron Collider and the RHIC have previously smashed into gold in search of similar results. These helium collisions were conducted in 2014, and have just now been published; the team conducted similar tests with single protons in 2015. The results of those collisions have yet to be published.

The ability to create an ever wider array of samples of quark-gluon plasma will be important, not because the plasma itself will ever be long-lived enough to be useful, but because the data gathered as it winks in and out of existence can offer a window into the very earliest events in the history of the universe. So, as interesting as it is that smaller collisions can create smaller, more localized droplets of quark-gluon plasma, the larger, stronger signals from larger impacts may be the primary interest for research.

Source: extremetech

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