High-energy particle collisions reveal the unexpected

Aug 08, 2014
High-energy collisions between nuclei (white arrows) produce a cloud of elementary particles including quarks (red) and gluons (yellow). When gluons form an expansion front, they can produce a wall of matter called a color glass condensate, which eventually dissipates as the expansion continues. Credit: © 2014 Larry McLerran, RIKEN–BNL Research Center

The nucleus of an atom is composed of protons and neutrons, which are themselves made up of elementary particles called quarks and gluons. Observing these elementary particles is difficult and typically involves smashing atoms together at close to the speed of light to observe emissions from high-energy collisions.

Larry McLerran from the RIKEN–BNL Research Center and Christian Klein-Boesing from the University of Münster in Germany have now shown that the production of photons in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) is consistent with a theory known as geometric scaling over an unexpectedly wide range of conditions.

A hypothesis arising from recent particle physics theory is that at extremely high energies, gluons could reach densities high enough to form an intermediate and exotic state of matter called a color glass condensate (Fig. 1), which is a precursor to other exotic states known as glasma and quark–gluon plasma. At high energies and densities, the color glass condensate also exhibits a property called geometric scaling, where physical quantities such as the rate of photon production scale with the size of the nucleus in a manner predicted by theory. "However, the expansion of the system should eventually promote the violation of geometric scaling," says McLerran.

The researchers showed that the photon yields of collisions conducted at the RHIC and LHC between two protons, two gold ions, two lead ions, or a gold ion and a deuteron (a nucleus containing one proton and one neutron) are consistent with the yields predicted by geometric scaling over a wider range of experimental conditions than previously expected. This result held true despite the large energy difference between the experiments at the two collider facilities. "The fact that our data exhibit geometric scaling suggests that photon production takes place early, before system expansion can dilute the effects of geometric scaling."

The finding has potentially important implications for quantum chromodynamics—a theory that describes the strong interactions underlying the physics of the nucleus. In particular, it could indicate that physicists have been making some wrong assumptions about the dynamics of photon production at the energies of RHIC and LHC collisions. The researchers suggest that the finding could indicate something very interesting and not yet understood about the evolution of glasma or , although more detailed computational simulations are needed to confirm the dynamics of photon production in such collisions.

Explore further: Smashing protons into lead ions creates quark-gluon plasma that behaves like liquid

More information: Klein-Boesing, C. & McLerran, L. Geometrical scaling of direct-photon production in hadron collisions from RHIC to the LHC. Physics Letters B 734, 282–285 (2014). DOI: 10.1016/j.physletb.2014.05.063

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George_Rajna
Aug 09, 2014
This comment has been removed by a moderator.
mikep608
1.6 / 5 (7) Aug 09, 2014
gluons don't exist. Protons are nat made of smaller particles. If protons were made from smaller particles, they wouldn't be identical. the tiny differences between protons that would result from being made from smaller particles would compound greatly when zoomed out to our level. There would be no uniform elements. What this experiment shows is that photons do not exist. It shows that an event that has the characteristics of what they define as the properties of photons occur. this is a reaction that eather has from atomic activity.
Whydening Gyre
3.7 / 5 (3) Aug 09, 2014
gluons don't exist. Protons are nat made of smaller particles. If protons were made from smaller particles, they wouldn't be identical. the tiny differences between protons that would result from being made from smaller particles would compound greatly when zoomed out to our level. There would be no uniform elements. What this experiment shows is that photons do not exist. It shows that an event that has the characteristics of what they define as the properties of photons occur. this is a reaction that eather has from atomic activity.

That protons all appear to have equal properties is an indication that what makes them up have no differences and therefore are the basic structures in this observable universe.
mikep608
5 / 5 (1) Aug 10, 2014
"That protons all appear to have equal properties is an indication that what makes them up have no differences and therefore are the basic structures in this observable universe."

And how did EVERY proton in the universe become EXACTLY alike then? This idea that they are made from smaller particles yet are identical is directly opposite of everything in nature that is made from smaller parts--they aren't exactly alike. on Earth, things that are close to each other evolve into seperate species, and this is just dealing with a few thousand to a million. Compare this to the fact that there are more protons in the universe then there are numbers to describe them in a very large area. What properties do these smaller particles have that they fit just perfectly so? not even the nucleus of an atom have arranged themselves in exact amounts, so why would these quarks?
Arties
3 / 5 (1) Aug 10, 2014
photon yields of collisions are consistent with the yields predicted by geometric scaling over a wider range of experimental conditions than previously expected
So that the better agreement with theory is presented as a surprise and unexpected finding? This is how the scientific journalism works. Nevertheless the pattern in which the particles follow the established theories just way too well is [ur=http://www.newscientist.com/article/mg21628923.800-higgs-boson-is-too-saintly-and-supersymmetry-too-shy.html]quite common[/url] in contemporary physics and it demonstrates the crash of theoretical speculations of the recent years.