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Quark-Gluon Plasma - QGP

Posted: Thu Feb 25, 2010 12:41 pm
by spencer

Re: Quark-Gluon Plasma - QGP

Posted: Thu Feb 25, 2010 1:37 pm
by Kasuha
positively charged quarks may prefer to emerge parallel to the magnetic field in a given collision event, while negatively charged quarks prefer to emerge in the opposite direction
It's a bit confusing here. Isn't "opposite direction" to "parallel to the magnetic field" also parallel to the magnetic field?
I guess they meant that one quarks tend to appear closer to south magnetic pole and other quarks closer to north magnetic pole because that's the only asymmetric thing I can imagine about it...?

Re: Quark-Gluon Plasma - QGP

Posted: Thu Feb 25, 2010 2:02 pm
by tswsl1989
A magnetic field has a direction (North to South), so opposite and parallel would be a line running the opposite way (South -> North)

Re: Quark-Gluon Plasma - QGP

Posted: Thu Feb 25, 2010 3:57 pm
by Kasuha
Yes but they did not mention poles, at least not in the article. "They're moving parallel to vertical" does not tell me if they're going up, down, or some up and some down.
So I assumed they meant poles and wanted to make sure.

Re: Quark-Gluon Plasma - QGP

Posted: Fri Feb 26, 2010 8:08 am
by chriwi
I think the magnetic fild generated by moving electric charges has no poles but only closed circlelike magnetic lines and the charged Quarks circle arround them the positiv in one direction, the negative in the other direction.

Re: Quark-Gluon Plasma - QGP

Posted: Fri Feb 26, 2010 9:48 am
by Tau
You're right. A magnetic field consists of field line loops. Normally, this loop is caused by a magnet, that contains part of the loop. But a moving charge in space with leave "floating" loops around its trajectory.
So in the above mentioned plasma each moving charge will make those loops, and the loops interact.
A magnetic monopole with be a beginning of a field line, by the way.

Re: Quark-Gluon Plasma - QGP

Posted: Fri Feb 26, 2010 12:52 pm
by Kasuha
chriwi wrote:I think the magnetic fild generated by moving electric charges has no poles but only closed circlelike magnetic lines and the charged Quarks circle arround them the positiv in one direction, the negative in the other direction.
Sure these are closed lines but they still got "towards south" or "towards north" direction - it's similar to going east or west on earth although there are no east or west poles too.

Re: Quark-Gluon Plasma - QGP

Posted: Thu Mar 25, 2010 5:46 pm
by rhody
I am new here, but not to physic's...

Just curious, to any physicist(s) participating in experiments that involve quark-gluon plasma, are you familiar with the work of Dr Glendenning ?

If so, what are your opinions of the following ?

Thanks in advance...


Sometimes a picture is priceless, from this Science Beat November 5, 2004 The Strange Insides of Neutron Stars

Dr. Normal Glendenning's home page

Found this today, some stuff may be old, some new, from:
Volume 27 - Issue 07 :: Mar. 27-Apr. 09, 2010
from the publishers of THE HINDU

This is the clearest most concise explanation of the timing and temperature of the jets I have seen to date, for me at least, and evidence of CP violation as well, see diagram in the link.

highlights below:

The temperature measurement was, however, based on the measurement by the PHENIX experiment. This temperature measurement, combined with other observations of the four experiments analysed over the nine years of RHIC’s operation, indicates that RHIC’s Au-Au collisions produce a freely flowing liquid QGP, according to a BNL press release. The QGP is believed to have filled the universe a few microseconds after it came into existence 13.7 billion years ago before cooling and condensing to form the protons and neutrons that make the matter we see around us, from atoms to stars, to planets and people. At RHIC, QGP liquid appeared and a temperature of 3 × 1012°C was reached in less than a billionth of a second, and the QGP itself lasted for less than a billionth of a trillionth of a second, the release said.
The temperature is inferred from the distribution of the frequency, or the energy, of the light emitted from the QGP liquid just like a hot iron rod emits a red glow. Since light interacts very little with the hot liquid, it is an accurate measure of the hot conditions within.

These data, according to Steven Vigdor of BNL, who oversees the RHIC programme, provide the first measurement of the temperature of the QGP at RHIC. According to him, the temperature inferred from these new measurements is considerably higher than the long-established maximum possible temperature attainable without liberating the quarks and gluons from their normal confinement inside individual protons and neutrons.

Theoretical predictions before the start of RHIC in 2000 expected that the QGP would exist as a perfect gas of free quarks, antiquarks and gluons. But analysis of data from RHIC’s first three years of operation produced the astonishing result that the matter behaved like a liquid whose constituent particles interact very strongly among them. The trajectories of the thousands of particles produced indicate that the particles produced tend to move collectively, more like the “flow” of a liquid in motion.

However, unlike ordinary liquids, in which individual molecules move about randomly, the hot QGP seems to move in a pattern that exhibits a high degree of coordination among the particles, somewhat like a school of fish. This liquid matter has been described as a nearly “perfect” liquid in the sense that it flows with almost no viscosity. Such a “perfect” liquid, however, does not fit in with the picture of free quarks and gluons that physicists had hitherto used to characterise the QGP.

Bubbles of broken symmetry

Another exciting, and related, finding from RHIC that throws new light on the nature of the QGP is the first evidence of profound symmetry transformations within the hot soup of quarks, antiquarks and gluons. This finding, which has been published in the journal Physical Review Letters, suggests that “bubbles”, or local domains, form in the hot strongly interacting matter of the QGP in the interiors of which parity, or “mirror symmetry” – a fundamental symmetry that says that the physics of a system and its counterpart in a mirror-reflected world should be the same – is violated.

Parity (P) symmetry and charge-parity (CP) symmetry, in which the mirror-reflected world also has all its particles replaced by their antiparticles, are known to be violated in the nuclear weak interaction that causes radioactive decay. However, there is no evidence to date of these symmetries being broken in strong interactions that bind quarks into protons and neutrons and hold the nuclei together. Although the theory of strong force, known as quantum chromodynamics (QCD), itself does not forbid P violation or CP violation in strong interactions, experiments so far have put very stringent limits on its occurrence.

“The key to observing the effect is to study correlations among the particles emerging from the collision,” says Nu Xu of Lawrence Berkeley National Laboratory, STAR experiment spokesperson. “We have observed a correlation among emitted charged particles of the predicted type, with the degree of directional preference increasing as the collisions vary from head-on to more grazing,” Xu added. STAR data also seem to suggest the local breaking of CP symmetry. If CP symmetry had not been broken at some early time in the evolution of the universe, the particles and antiparticles that were created in equal numbers during the Big Bang would have annihilated each other in pairs, leaving no matter to form the stars and planets we see today.


Some small violations of CP symmetry have been seen in previous experiments as well, but these are too weak to explain matter dominance in the universe. Likewise, STAR finding too does not provide an explanation for that but may offer some insight into how such symmetry-breaking occurs. According to Vigdor, the features observed at STAR were found to be qualitatively consistent with predictions of symmetry-breaking domains in hot quark matter.

Theorists were long in the habit of thinking of this phase change — from the confined-quark to the deconfined-quark stage — as analogous to phase changes in water, for example from liquid water to ice. In the case of a neutron star, it was assumed, pressure increases smoothly with depth, until at some point neutron matter makes a smooth transition to quark matter.

If phase changes in water occurred in a system with two oppositely charged components, instead of freezing from the top down, spheres of ice would form.
But phase changes in water, says Glendenning, "are first-order transitions with only one independent component" — namely water itself. "In the real world, this kind of transition is far from typical. The situation is much more interesting for substances with two or more components."

Going through a phase
The stuff of a neutron star, for example. One of the two components that vary in neutron-star phase changes is electric charge. While neutron stars are globally neutral, local regions could have excesses of positive or negative charge.

A second component is baryon number, which must also be conserved. Hadrons have positive baryon numbers, while their antiparticles have negative baryon numbers.

There is no simple correspondence between electric charge and baryon number. A neutron has a positive baryon number but no electric charge; up and down quarks both have a fractional baryon number (plus 1/3), but an up quark's electric charge is plus 2/3, and a down quark's is minus 1/3.

Because of this two-component system — the hadronic matter and the quark matter — the stuff of a neutron star can make trade-offs locally to maintain overal global electrical neutrality and conserve baryon number. Between the star's outer, quark-confined regions and its innermost, quark-deconfined regions, there will be mixed phases, mixed hadronic and quark matter that take on fantastic geometries.
Hadron regions like to maintain an equal number of neutrons and protons. This is not possible globally but is approachable locally, where hadronic matter begins to mix with quark matter, because under extreme pressure neutrons can become protons by transferring electric charge to quarks — changing up quarks into down or strange quarks, for example. The result is a region of positively charged nuclear matter with negatively charged quark matter embedded in it.

Glendenning uses a vivid metaphor to describe how different a two-component phase change is from the one-component phase changes of water: "Suppose water had two independent components and one of them was electric charge, with opposite charge on the ice than on the water. Then a lake would not freeze over starting with a sheet of ice on top, but ice spheres would form throughout the volume of the lake, of slightly different size and spacing from top to bottom, because of the pressure gradient."

Glendenning theorizes that in a neutron star of the right mass and density, a crystal of hadronic and quark matter in mixed geometric configurations occupies the region between outer nuclear matter and inner quark matter. Likewise, where hadronic matter and quark matter are mixed, if quark matter is in the minority the quarks are segregated as droplets in a crystalline array, each droplet at a lattice point. As the pressure increases the proportion of quark matter increases and the droplets elongate to rods; still more pressure means still more free quarks, and the rods join into slabs.

As pressure continues to increase, quark matter becomes the dominant phase, and the hadrons inside it form slabs, rods, and finally droplets, just before the system turns to pure quark matter. Glendenning jokingly refers to this as a pasta model: "Drops like orzo, rods like spaghetti, slabs like lasagna."

The picture of neutron star interiors based on two-component phase transitions is not intuitive (nothing about neutron stars is), and while Glendenning says he's astonished everybody before him missed it, he admits it took him five years to realize it himself.