The STAR collaboration at the RHIC has published an analysis of factors that affect the flow of particles from heavy ion The results of the physical review letters will help the scientists zero in on key properties of a unique form of matter that mimics the early universe.
A trillion-degree soup of quarks and gluons is what physicists are interested in. These are the components that make up the protons and neutrons of atomic nuclei. The hot quark soup is created by colliding beams. Scientists can study the quarks and gluons as they were 14 billion years ago thanks to the collisions.
A facility that can vary the beam energy and collide different kinds of ion allows us to change the temperature and density of the hot blob of quark matter. It's possible to tell us more about the properties of the matter we've created by studying what happens under those different conditions.
Don't go with the flow.
The scientists were interested in the flow of debris from the smashups. Nuclear physicists have observed that off-center collisions push more particles out along the reaction plane of the colliding nuclei than they would if the nucleus were parallel to it. The elliptic flow patterns were important to the discovery that the Q GP behaves as a liquid with a low viscosity.
The simplistic picture shows the flow isn't as smooth as it could be. There are many changes. Scientists will be able to calculate the plasma's properties much more precisely if they nail down the source of the fluctuations.
"The fluctuations could come from the initial state, when the ion collides first, or they could develop while QGP is evolving, or they could develop when the system produces the particles we track in our detector," said Roy Lacey. You can learn where the fluctuations come from by carefully choosing the measurements.
The source is being tracked.
Scientists studied flow patterns from a variety of RHIC operations to tease out the contributions.
They looked at how central or off-center the ion struck one another in the data. Scientists can see the influence of initial state effects with this exercise.
They looked at the flow patterns in the collisions of the same ion system. If you see a difference in flow patterns by energy, you'll see that the blob of hot matter is evolving.
The flow patterns of different species of particles hitting the detector were tracked. As the Q GP transitions back into particles made of quarks and gluons, there will be fluctuations.
Flow fluctuations are dependent on the state of the collision.
The most influential thing is how central the collision are. There is a football-shaped overlap region where the pressure is stronger on the short axis of the football than on the long axis. The pressure gradient pushes more particles out of the plane than before. The analysis accounts for the variability of the zone.
There are a lot of small balls hitting each other. It appears to be an ellipse shape, but there is variability around the edges.
Lacey said that lumpiness influences fluctuations in the flow of particles that eventually emerge.
Small nuclei are more likely to generate larger flow fluctuations than large nuclei.
The flow patterns that were shown in the analyses were not affected by collision energy or particle species.
Magdy said that this is the first time that they have been able to combine the data from the beam energy scans and the collision of different systems.
There are implications.
The scientists will be able to make more precise calculations of the quark-gluon plasma's properties now that they know the initial state conditions are the main cause of the flow fluctuations.
Lacey said that they are now able to put better constraints on the magnitude of the properties.
The process of mapping out the phases of any type of matter is similar to that of quark matter.
Lacey said that the more precise measurement will help narrow down whether or not there are phases in nuclear matter.
Scientists may be able to discover if there is a critical point in the nuclear phase diagram if they put tighter constraints on the measurement of viscosity. The type of phase change from ordinary nuclear matter to QGP itself changes from a first-order transition to a second-order transition. There is a smooth transition between hadrons and Q GP. Physicists will be able to look for a dip in shear viscosity that is expected to occur at this point on the map of nuclear phases with the help of precision measurement of viscosity.
Lacey said that they will use the new constraints and model comparisons to move in that direction.
Magdy said, "This new analysis is challenging the models to provide an explanation that will accommodate this comprehensive set of data so we can gain a better understanding of the properties and evolution of the quark-gluon Plasma."
There is more information in the Physical Review Letters. There is a book titled "PhysRevLett.129.252301."
Journal information: Physical Review Letters
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