First indirect evidence of so-far undetected strange baryons

Aug 19, 2014
Brookhaven theoretical physicist Swagato Mukherjee. Credit: Brookhaven National Laboratory

(Phys.org) —New supercomputing calculations provide the first evidence that particles predicted by the theory of quark-gluon interactions but never before observed are being produced in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC), a facility that is dedicated to studying nuclear physics. These heavy strange baryons, containing at least one strange quark, still cannot be observed directly, but instead make their presence known by lowering the temperature at which other strange baryons "freeze out" from the quark-gluon plasma (QGP) discovered and created at RHIC, a U.S. Department of Energy (DOE) Office of Science user facility located at DOE's Brookhaven National Laboratory.

RHIC is one of just two places in the world where scientists can create and study a primordial soup of unbound quarks and gluons-akin to what existed in the early universe some 14 billion years ago. The research is helping to unravel how these building blocks of matter became bound into hadrons, particles composed of two or three quarks held together by gluons, the carriers of nature's strongest force.

"Baryons, which are hadrons made of three quarks, make up almost all the matter we see in the universe today," said Brookhaven theoretical physicist Swagato Mukherjee, a co-author on a paper describing the new results in Physical Review Letters. "The theory that tells us how this matter forms-including the protons and neutrons that make up the nuclei of atoms-also predicts the existence of many different baryons, including some that are very heavy and short-lived, containing one or more heavy 'strange' quarks. Now we have indirect evidence from our calculations and comparisons with experimental data at RHIC that these predicted higher mass states of strange baryons do exist," he said.

Added Berndt Mueller, Associate Laboratory Director for Nuclear and Particle Physics at Brookhaven, "This finding is particularly remarkable because strange quarks were one of the early signatures of the formation of the primordial . Now we're using this QGP signature as a tool to discover previously unknown baryons that emerge from the QGP and could not be produced otherwise."

Freezing point depression and supercomputing calculations

The evidence comes from an effect on the thermodynamic properties of the matter nuclear physicists can detect coming out of collisions at RHIC. Specifically, the scientists observe certain more-common strange baryons (omega baryons, cascade baryons, lambda baryons) "freezing out" of RHIC's quark-gluon plasma at a lower temperature than would be expected if the predicted extra-heavy strange baryons didn't exist.

"It's similar to the way table salt lowers the freezing point of liquid water," said Mukherjee. "These 'invisible' hadrons are like salt molecules floating around in the hot gas of hadrons, making other particles freeze out at a lower temperature than they would if the 'salt' wasn't there."

To see the evidence, the scientists performed calculations using lattice QCD, a technique that uses points on an imaginary four-dimensional lattice (three spatial dimensions plus time) to represent the positions of quarks and gluons, and complex mathematical equations to calculate interactions among them, as described by the theory of quantum chromodynamics (QCD).

"The calculations tell you where you have bound or unbound quarks, depending on the temperature," Mukherjee said.

The scientists were specifically looking for fluctuations of conserved baryon number and strangeness and exploring how the calculations fit with the observed RHIC measurements at a wide range of energies.

The calculations show that inclusion of the predicted but "experimentally uncharted" strange baryons fit better with the data, providing the first evidence that these so-far unobserved particles exist and exert their effect on the freeze-out temperature of the observable particles.

These findings are helping physicists quantitatively plot the points on the phase diagram that maps out the different phases of nuclear matter, including hadrons and quark-gluon plasma, and the transitions between them under various conditions of temperature and density.

"To accurately plot points on the phase diagram, you have to know what the contents are on the bound-state, hadron side of the transition line-even if you haven't seen them," Mukherjee said. "We've found that the higher mass states of strange baryons affect the production of ground states that we can observe. And the line where we see the ordinary matter moves to a lower temperature because of the multitude of higher states that we can't see."

Explore further: High-energy particle collisions reveal the unexpected

More information: "Additional Strange Hadrons from QCD Thermodynamics and Strangeness Freezeout in Heavy Ion Collisions" journals.aps.org/prl/abstract/… ysRevLett.113.072001

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User comments : 12

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GuruShabu
1 / 5 (11) Aug 19, 2014
"New supercomputing calculations provide the first evidence that..."
How can be a simulation be considered a "evidence"?
This is closer to day-dreaming than "science"!
Osiris1
1 / 5 (4) Aug 19, 2014
I would say this is a good candidate for 'dark matter'.
Osiris1
2 / 5 (4) Aug 19, 2014
We know next to nothing about just what 'dark matter' IS. It would be folly not to pursue every lead. Know you that out of 'day dreaming' have come many if not most of the scientific breakthroughs achieved by man.
Toiea
3.3 / 5 (7) Aug 19, 2014
I would say this is a good candidate for 'dark matter'.
I'd say, these particles would be the worst candidate for dark matter - they're terribly heavy and short-living.
Steve 200mph Cruiz
4.3 / 5 (7) Aug 19, 2014
What are you guys talking about? This has nothing to do with dark matter.

"New supercomputing calculations provide the first evidence that..."
How can be a simulation be considered a "evidence"?
This is closer to day-dreaming than "science"!


The title clearly says "indirect evidence", this is physics, that means it's ALL math. Because of the definition of what physics is, you can use a super computer (which is really more like a kick ass graphing calculator), enter the equations with defined variables and see what happens.
Mimath224
1 / 5 (3) Aug 19, 2014
@Steve 200mph Cruiz...mathematical phyisics eh? But I do agree with you about the DM post. Actually, because of the chemical analogy given in the article the lowering of temperature imo is more likely to be about entropy than DM, that is, most chemical reactions are exothermic where endothermic reactions are an increase in 'order'. Wonder if it might be similar for the qgp? If so then these calculations might give us a little bit more insight to conditions in the early universe.
Psilly_T
2 / 5 (3) Aug 20, 2014
well just shooting an idea out there..not claiming its right. If gas rushes to DM densities early in the universe would these areas not be cooler if the area was littered with these heavy cold inducing particles where the gasses could condense to form stars and galaxies etc. possible link? meh I dunno, a lot of you say no way so what ever.
antialias_physorg
5 / 5 (4) Aug 20, 2014
How can be a simulation be considered a "evidence"?

The simulation matches the observed data. Which makes the thing that is simulated a hot contender.

if the area was littered with these heavy cold inducing particles

Where do you get the notion of 'cold inducing' from?
Osiris1
1 / 5 (1) Aug 22, 2014
When one 'does something that works' and obtains a candidate for the 'unobservable', then one can produce this for testing any number of times. If I was a DM researcher and had this in MY lab, you would better believe that my staff would work with this, test purported detection device ideas on it, etc. And we would do this until we had a good detector that we could use to find the same stuff 'in the wild'.
Toiea
2.3 / 5 (3) Aug 22, 2014
If I was a DM researcher and had this in MY lab
IMO Nicola Tesla has been the first researcher of dark matter. The DM particles (scalar waves) can be prepared rather easily: you need the Dirac fermions or magnetic monopoles and electric pulses (a transient, not alternative electric field). In practical research you should start with phenomena, which work well in the kitchen and to gradually expand/extrapolate to areas, which are more experimentally demanding. The mainstream scientists are doing exactly the opposite (partially due to their fringe interpretation of SUSY and effort to substantiate the stringy models with it).
pepe2907
5 / 5 (1) Aug 22, 2014
""New supercomputing calculations provide the first evidence that..."
How can be a simulation be considered a "evidence"?"
"Calculations", not "simulations" and they "reveal", not "are considered", because everything in QM is probabilistic by nature and the probability of these rare occurrences is very very small. So they need a lot of calculations to find the small difference in the results between "what would be" with and without this particular phenomena and to make this calculation for a huge number of events /collisions/...
mikep608
1 / 5 (1) Aug 23, 2014


"RHIC is one of just two places in the world where scientists can create and study a primordial soup of unbound quarks and gluons-akin to what existed in the early universe some 14 billion years ago. The research is helping to unravel how these building blocks of matter became bound into hadrons, particles composed of two or three quarks held together by gluons, the carriers of nature's strongest force."

EWhat a bunch of bullshit. Aren't these supposed to be the particles that decay in microseconds, and they were supposed to be bouncing off of eachother during the Big Bong?