Image courtesy of Brookhaven National Laboratory Initial hot spots created by collisions of one, two, and three-particle ions with much larger gold ions (top row). Expected patterns if the collisions are creating tiny hot spots of the primordial soup, or quark-gluon plasma.
Surprisingly, smaller particles colliding with large nuclei appear to produce tiny droplets of quark-gluon plasma (QGP). Recent results show that the tiny droplets behave like a liquid not the expected gas. The results support the case that these small particles produce tiny drops of the primordial soup.
Smashing large atomic nuclei, containing protons and neutrons, together at close to the speed of light re-creates the conditions of the very early universe. It was thought that only the nuclei of large atoms such as gold would have enough matter and energy to produce a primordial soup of matter’s most basic “quark” and “gluon” building blocks. But smaller particles colliding with large nuclei produce tiny droplets of QGP.
Experiments are revealing the key elements required for creating QGP and could offer insight into the initial characteristics of the colliding particles. The discovery of elliptic-shaped flow in particles streaming out of Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab, when gold nuclei collided showed that that the matter created in these collisions behaved like a liquid rather than the expected gas. Additional experiments confirmed that this liquid is indeed composed of visible matter’s most fundamental building blocks, quarks and gluons, and that the flow occurs with minimal resistance – making it a nearly “perfect” liquid plasma.
The RHIC scientists caused He-3 nuclei (2 protons, 1 neutron) to collide with gold and single protons with gold to discover a triangular pattern of flow that is consistent with the creation of tiny QGP. These small particle collisions could be producing the extreme temperatures required to free quarks and gluons – albeit at a much smaller, more localized scale than in the relatively big domains of QGP created in collisions of 2 heavy ions.
Because not all of the key signatures of QGP formation exist, scientists at the RHIC are continuing to study colliding protons with gold ions – to explore whether there are other interesting phenomena occurring in these collisions in addition to particle flow. There’s widespread agreement that the measurements at RHIC. http://science.energy.gov/np/highlights/2015/np-2015-08-a/
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