Scientists model the 'flicker' of gluons in subatomic smashups

Scientists model the 'flicker' of gluons in subatomic smashups
Four snapshots of the gluon density in a proton at high energy, as modeled by Mäntysaari and Schenke. Red indicates high gluon density, blue indicates low density. Credit: Brookhaven National Laboratory

Scientists exploring the dynamic behavior of particles emerging from subatomic smashups at the Relativistic Heavy Ion Collider (RHIC)-a U.S. Department of Energy Office of Science User Facility for nuclear physics research at DOE's Brookhaven National Laboratory-are increasingly interested in the role of gluons. These glue-like particles ordinarily bind quarks within protons and neutrons, and appear to play an outsized role in establishing key particle properties.

A new study just published in Physical Review Letters reveals that a high degree of gluon fluctuation-a kind of flickering rearrangement in the distribution of gluon density within individual protons-could help explain some of the remarkable results at RHIC and also in experiments at the Large Hadron Collider (LHC) in Europe.

Right now it's impossible to directly "see" the distribution of gluons within individual protons and nuclei-even at the most powerful particle accelerators. So Brookhaven Lab theoretical physicists Björn Schenke and Heikki Mäntysaari developed a mathematical model to represent a variety of arrangements of gluons within a proton.

"It is very accurately known how large the average gluon density is inside a proton," Mäntysaari said. "What is not known is exactly where the gluons are located inside the proton. We model the gluons as located around the three valance quarks. Then we control the amount of fluctuations represented in the model by setting how large the gluon clouds are, and how far apart they are from each other."

The fluctuations represent the behavior of gluons in particles accelerated to high energies as they are in colliders like RHIC and the LHC. Under those conditions, the gluons are virtual particles that continuously split and recombine, essentially flickering in and out of existence like fireflies blinking on and off in the nighttime sky.

Scientists would like to know if and how these fluctuations affect the behavior of the particles created when protons collide with heavy nuclei, like the gold ions accelerated at RHIC. Data from RHIC's proton-gold collisions, and from the LHC's proton-lead collisions, have shown evidence of "collective phenomena"-particles emerging with some "knowledge" of one another and in some preferred directions rather than in a uniform fashion. In RHIC and LHC smashups of two large particles (gold-gold or lead-lead), this collective behavior and direction-dependent flow has been explained by the liquid state of quarks and gluons-the "perfect liquid" quark-gluon plasma (QGP)-created in these collisions. But collisions of tiny protons with the larger nuclei aren't supposed to create QGP. And the current understanding of the QGP can't completely explain the experimental results.

"If we want to understand what happens, we have to know the geometry of the proton just before the collisions. It makes a difference if you have a round object hitting a nucleus vs. something with a more irregular structure hitting the nucleus," Mäntysaari said. "The collective behavior we see in the experiments might imply that there is some more complex structure to the proton," he added, noting that exploring the internal structure of the proton is a fundamental research endeavor for nuclear physicists.

The model developed by Mäntysaari and Schenke describes how the proton structure can fluctuate. To test the model, they turned to a different set of experimental data-results from collisions of electrons with protons at the HERA accelerator in Germany. A particular reaction that sometimes occurs in these collisions-where a particle called a J/psi is produced and the proton breaks up into a spray of other particles-is highly dependent on the level of structural fluctuations in the proton.

The Brookhaven theorists used their model to predict the frequency of this interaction while varying the level of gluon fluctuations, and compared their calculations with the experimentally observed data. They found that the version of their model with the highest degree of fluctuations was the one that fit the data best.

"This process doesn't happen at all if the proton always looks the same. The more fluctuations we have, the more likely this process is to happen," Mäntysaari said.

He and Schenke are now looking to apply this knowledge to the proton-nucleus collisions.

"When the gluon fluctuations are incorporated into the hydrodynamic models of QGP, we get a better agreement with the experimental data from these proton-nucleus collisions," Mäntysaari said.

As Schenke noted, "This implies that the formation of a strongly interacting QGP in proton-nucleus collisions provides a possible explanation of the experimentally observed collectivity."

If the nuclear physics community gets to build a proposed future project called an Electron-Ion Collider (EIC), they'll have an opportunity to improve on the precision of these results.

"An EIC will allow us to measure this more precisely, and in different kinematics-how the depend on energy, for example," Mäntysaari said. "And an EIC can also do the same kind of studies in nuclear targets to see how much the structure of the nucleus fluctuates event by event."

In essence, the EIC would be a true gluon-imaging machine-a way to directly probe the internal structure of the building blocks of visible matter, including the glue that binds everything in the universe today.


Explore further

Physicists zoom in on gluons' contribution to proton spin

More information: Heikki Mäntysaari et al, Evidence of Strong Proton Shape Fluctuations from Incoherent Diffraction, Physical Review Letters (2016). DOI: 10.1103/PhysRevLett.117.052301
Journal information: Physical Review Letters

Citation: Scientists model the 'flicker' of gluons in subatomic smashups (2016, August 2) retrieved 25 June 2019 from https://phys.org/news/2016-08-scientists-flicker-gluons-subatomic-smashups.html
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Aug 02, 2016
Really, and how do you know it's not just radiation due to the motion of a charge?

Aug 02, 2016
I suspect there is a neutral particle sitting at the near center of the proton...

Aug 02, 2016
Very interesting. This implies that nuclei are quark-gluon plasmas without settled identities or even positions for the neutrons and protons in them; essentially they are composite particles.

Aug 03, 2016
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Aug 03, 2016
This comment has been removed by a moderator.

Aug 03, 2016
To all, Why and how? I'd like to build the instrumentation to control this phenom.

Aug 04, 2016
To all, Why and how? I'd like to build the instrumentation to control this phenom.

I'm sure the simulator has a dial on it....but if you mean real world applicability, there is none as the only stable product from atom smash ups are photons.....

OK, the proton and gluon combo is illogical, the net is always positive, therefore a non performer as insufficient. The neutron is a proton and electron capture in the atomic confinement. i. e. the negative field and the positive field that was unknown when some PhD stated that the neutron has zero charge; therefore, unnecessary. So theoretically illogical, does not provide necessary and sufficient conditions to define truth. QED silly wabbit

Aug 04, 2016
As for photons, I accept the definition as a point upon the sphere surrounding the emitter, i.e. in fact none of these so called particles need exist, none are necessary or sufficient. But then, most don't get it since they only know the toys taught to them but never given certainty. So the concept of particle has no meaning. It's not like a particle of my mom's cake. Quanta is something man made up. Quanta has no existence. It's a discretization of the continuous field. If you were paying attention in class you will recall concepts vs reality.

Aug 04, 2016
It's a discretization of the continuous field.

No argument here sir. It is only done so that it can be represented mathematically.

I'm beginning to like you. You do understand the multiple misconceptions and misinterpretations of QM, GR, BB, and the SM. So modern physics requires a complete rewrite. Now we can do this; however, how do we handle what we are using? There exist some truth by measurement, like gravity; however, not holistic. Atomic physics is a shambles. So what do you mean when you say represented mathematically? juz say'n

Aug 06, 2016
This comment has been removed by a moderator.

Aug 07, 2016
Oh, look! It's a home-schooled-piece-of-shite convention.

What's the Victorian collective noun for that? A dram of dolts? An assemblage of arsehats?

Think we can use this within our list of the most exotic quotes from the least of us. Could be the reason we look for dark whatever.

Aug 07, 2016
Very interesting. This implies that nuclei are quark-gluon plasmas without settled identities or even positions for the neutrons and protons in them; essentially they are composite particles.
I do not understand. Do you mean to say instead that
"nucleons are quark-gluon plasmas without settled identities or even positions for the quarks and gluons in them" ?
No; most people have this vision (promoted by pop-sci pictures) of a ball of neutrons and protons. I think you and I know that it's a quark-gluon plasma, but I think most people don't think of it that way. This article (not to mention the science underlying it) gives a view of that, and that's what I was commenting on.

Aug 07, 2016
@ Da Schneib What about the shell model and the resulting self-consistent field calculations? Wouldn't the shell model fail completely if the quarks and gluons were not nearly bound within nucleons? How do you explain magic numbers and the prediction of the stability of the super heavies?

Aug 07, 2016
@ Da Schneib What about the shell model and the resulting self-consistent field calculations?
All based on underlying symmetries of the quarks and gluons. We're just starting to investigate this in concrete terms with lattice QCD due to bare QCD's analytic intractability. This article shows pretty much the forefront of this avenue of research.

Wouldn't the shell model fail completely if the quarks and gluons were not nearly bound within nucleons?
No. Because it's based on the underlying physics of QCD, the shell model gives predictions that match reality; but it's the details that are lacking.

How do you explain magic numbers and the prediction of the stability of the super heavies?
They emerge from QCD. How is exactly what we're finding out in experiments and theoretical calculations like the ones documented here.

Aug 07, 2016
@hyperfuzzy (about bullshit)
You do understand the multiple misconceptions and misinterpretations of QM, GR, BB, and the SM.

Why, of course. He is a prominent propagator or even author of hem.
Here they are: https://www.youtu...5OdguJro

Perfect

Aug 07, 2016
Da Schneib Of course, QCD is the underlying theory. I thought we were talking about the degree of localization and delocalization of the constituent elementary (quarks and gluons) and their mean free paths. At the time scale of the experiments, even the gluons seem to be mainly localized about the quarks. When I think of a quark-gluon "plasma" approach, I think of the quarks and gluons as being delocalized over the size of the nucleus. Perhaps, I have misinterpreted your comments.

Aug 07, 2016
I'd be interested to see if any of the physicists who post here occasionally can tell us whether we know enough to figure the uncertainty of position of the quarks and gluons in the nucleus and tell us more than the obvious: that the uncertainty in position must be smaller, in most cases, than the size of the nucleus. (I say in most cases because of radioactive decay of some nuclei.) I'd be surprised if we know enough to state what the mean free path might be other than to constrain it to the size of the nucleus.

Aug 08, 2016
Really, and how do you know it's not just radiation due to the motion of a charge?

Because we'd see every atom glowing like crazy if it were. We don't. So it's not.

What's the Victorian collective noun for that? A dram of dolts? An assemblage of arsehats?

It's called a ship of fools
https://en.wikipe...of_fools
Or for those who remember the Far Side cartoons: A car of idiots
http://4.bp.blogspot.com/-qWDmf63y408/VZhFnMTA6HI/AAAAAAAAD3I/ZPU0UmF7akk/s1600/farside%2B001.jpg

Aug 08, 2016
I don't think a nucleus is a quark gluon plasma. It is more like a molecular fluid held together by van der Waals forces.
How are they different? Just how much energy, or are there dynamic differences?

Aug 08, 2016
Da Schneib: there's a definitive difference between a QGP and Protons. In a QGP, quarks are entirely free to flow within the medium. When a QGP 'freezes out,' these quarks bind up into discrete hadrons (protons, neutrons, pions, eg). Gluons still flow within a hadron between the quarks, and also between hadrons, binding them together (not entirely unlike photons holding an electron to a molecule, but also passing between molecules to hold them more weakly together).

This study is meant to look at how quarks move between the hadrons of a nucleus. We'll know more when we build an electron-ion collider that allows us to use electrons as high energy probes of the nucleus.

Aug 08, 2016
So even within the confines of a nucleus, the protons and neutrons retain their identities? That's what I was talking about; a lone proton can't be a QGP, due to confinement.

Aug 08, 2016
Really, and how do you know it's not just radiation due to the motion of a charge?

Because we'd see every atom glowing like crazy if it were. We don't. So it's not.

What's the Victorian collective noun for that? A dram of dolts? An assemblage of arsehats?

It's called a ship of fools
https://en.wikipe...of_fools
Or for those who remember the Far Side cartoons: A car of idiots
http://4.bp.blogspot.com/-qWDmf63y408/VZhFnMTA6HI/AAAAAAAAD3I/ZPU0UmF7akk/s1600/farside%2B001.jpg

Good read

Aug 08, 2016
This comment has been removed by a moderator.

Aug 08, 2016
So even within the confines of a nucleus, the protons and neutrons retain their identities?


Yes, with the usual caveat that identical particles are indistinguishable, so it only makes sense to speak of a nucleus with Z protons and N neutrons. But they are "separate" particles. Any one particle isn't meaningfully a QGP, nor is a proton-ion collision expected to be sufficient energy density to melt the protons and neutrons into a QGP either. (A simplified version of this calculation was a really cool exercise in grad QM, where you can show how you need both high particle density and high energy to melt hadrons).

What this study seems to be saying is that sometimes, the gluon density seems higher than you might expect, and maybe that throws off when we should expect QGPs to form in collisions.

Aug 08, 2016
Wow, since we're just shooting the breeze, when I took QM, BSEE, I was also taking modern physics, thus with what theory was used for each left plenty of unanswered questions. Best course EM theory. However, I can disprove modern physics. I recognized that QM had it almost correct, use a wave equation, of course, no theory, it works, except for the man made creations to fit some model, as well as the misinterpretations of what is a particle, i.e. we were talking about energy in a cavity with the cavity defining the limitations, not the actual atoms. Did I mention in each case a comprehensive theory for the source of gravity was never defined to my liking. Add Einstein's corpuscular theory to the mix and the slit experiment and the creation of the nonexistent photon and the asinine change space and time to fit the data, a cheat, with an unproven assumption and poor knowledge of the actual subject. This is what we get. Nonsense.

Aug 08, 2016
So we are left with this being taught in grad school and no one see's the errors in a dubious science defined as particle physics, a physics of the non-existent and the illogical, seeking to define reality with science that allows time travel and reshaping space and time. Sure, that makes sense, genius. Funny

Aug 09, 2016
what do you mean when you say represented mathematically? juz say'n

Mathematically, mainstream physics describes everything as a point held together by smaller points

Baloney.

Here's a point, a point is a geometrical representation of nothing; however, with proper dimensions and attributes it may be able to define where and when. To assign any other properties you must define your space and your universe of discourse, logically; else, your statement makes no sense, i.e. mathematically speaking. Note: The logic I used is the Formal Logic. Please state yours, include you method for measuring truth. I use [1,0] You may define whatever you wish. But it must be defined to be proper math.

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