Wednesday, August 23, 2006

Quark Gluon Plasma

In absence of quality thinking time, I will provide you with one of my favorite shortcuts to thinking: pictures. In this case, I found some particularly nice pictures in one of Stefan's talks. They depict very nicely the difference between common hadronic matter and the quark gluon plasma.

The possibility to produce a state of matter as hot and dense as it was in the first moments of the universe is one of the primary goals for Heavy Ion collisions. For this purpose, heavy nuclei like those of lead and gold, are collided with highest energies and form an intermediate hot and dense state, the so-called fireball. The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) performs such experiments, with which we hope re-create conditions similar to those in the very early universe.

The top energy for the collision of gold nuclei at RHIC is about 200 GeV per nucleon. Such a gold nucleus consists of 197 nucleons (79 protons and 118 neutrons), which adds up to 40 TeV: that is roughly the energy of a mass of 10 milligram (a grain of coarse salt) falling from a height of 2.5 cm (or 1 inch), its macroscopic!

In a head-on, central collision with such an energy, some 1000 particles are produced. The tracks of the charged particles are measured in the large detectors, and they typically look like this:



(picture credits go to Jens Berger, from the STAR team)


Naive as I am, I always thought there are ten-thousands of nuclei in such a collision, but actually the number is roughly 70.

Matter in the particle beam before the collision is present in its usual form of nuclei, which consists of neutrons and protons. In this state, the quarks are confined to these color-neutral bound states, which are called hadrons. This usual matter, which consists of protons and neutrons, is called hadronic matter. The fireball created in the collisions is so hot and dense, that it is expected to allow the quarks to move almost freely, thus removing the confinement into hadrons. This state, then is called the quark gluon plasma. The pictures below show both possibilities.

This is hadronic matter:


where the grey bubbles indicate the color-neutral hadrons, inside which you see the valence quarks (large) and further virtual colored particles - so called sea quarks, and gluons. The arrows indicate the isospin of the quarks. The protons and neutrons consist of up and down quarks, with isospin +1/2 (up quark), and isospin -1/2 (down quark), respectively.

This, in contrast is the quark gluon plasma:

Here the colored constituents are able to move freely within the blob of heated, deconfined matter. The initial temperature of the fireball which creates such extreme conditions is some hundred MeV. My unit converter says that is about 1013 Kelvin, a pretty hot soup.

The challenge for the theoretical physicists is now to come up with observables, which allow to distinguish in which form the matter was present in the fireball. After all, in the dectors, nobody has ever found an isolated quark, its always hadrons.

At RHIC, it is now quite sure that matter is not hadronic any more in the collision. But what it is instead, that is still not completely clear. At the moment, the state of matter created is dubbed a quark gluon liquid, which is a a liquid of strongly interacting quarks and gluons rather than a gas of weakly interacting quarks and gluons. If someone has a picture for that, I'd really like to see it.



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20 comments:

QUASAR9 said...

Wow! Bee excellent post.
You've stolen my thunder, I cannot possibly to it any better. I'll have to bow and refer a link to this post.

Stefan the pictures are excellent, I may still need to ask your permission for use on the same topic on some future post.

You could say for now I'm redshifting behind Bee who is clearly travelling at the speed of light. - Q

QUASAR9 said...

Re comment at my place:

Hi Bee,
my apologies for having omitted your
More about Extra Dimensions
I had read it, when you posted it and enjoyed it, but the link slipped my mind. I've now added it to my post. Thanks!

I shall be taking a second read of:
minimal length model

Bee, You are a gem, not just providing useful links but providing helpful posts I can link to. Thanks!

Bee said...

Hi Quasar,

thanks so much for the nice words :-) It makes me realize that it's worth the effort.

These days my speed of light is energy dependent. It can even reach infinity...

Best,

B.

stefan said...

Stefan the pictures are excellent, I may still need to ask your permission for use on the same topic on some future post.

Hi quasar, I am happy that you like them. Feel free to use the - just give me the credits, that would be nice. And:

Now that I look at them again, I think it's important to keep in mind that they are more a mnemonic than a true representation of the physical constitution of a hadron, which is a really complicated object of interacting coloured things.

paul valletta said...

Stefan, the constituency of the Quark Gluon "soup" , do you think should be called Quark "GLUTON" ?

Amazing pictures, does not really capture though, the fact that a new phase of matter at specific temperature, is an intermediate product?

Virtual Gas = Virtual Solid = Virtual Liquids, for High temperatures, just as for Cold temperatures?

Is the density of "Hot" Quark_Gluons, equal to that of "Cold" Quark_Gluons ?

It is sure to note that a hot Plasma (phase of matter), can be of the same constituency of a cold Plasma (Bose_Einstein_Condensate) ?

Cold 'Fusion' emerges from Hot 'fission' ?

paul valletta said...

Please forgive me, I am having some computer problems!

http://en.wikipedia.org/wiki/Colour_confinement

Is needed to explain some Bossa Nova:

http://en.wikipedia.org/wiki/Hadronization

the "grey" area is a confinment field

Bringing "hot" particulates together constitutes :

The confining phase is usually defined by the behavior of the action of the Wilson loop, which is simply the path in spacetime traced out by a quark-antiquark pair created at one point and annihilated at another point. In a non-confining theory, the action of such a loop is proportional to its perimeter. However, in a confining theory, the action of the loop is instead proportional to its area. Since the area will be proportional to the separation of the quark-antiquark pair, free quarks are suppressed.

http://en.wikipedia.org/wiki/Schwinger_model

Yet in a condensate, the above statement could also be true for Bossa Nova ?

Handwaving to non colliding interactions ;)

QUASAR9 said...

perfect low viscosity

In three spatial dimensions, it is a close relative of the quark-gluon plasma, the super-hot state of matter that hasn't existed since the tiniest fraction of a second after the big bang that started the universe.
When viewed in 10 dimensions, the minimum number prescribed by what physicists call "string theory," it is a black hole.

Uncle Al said...

Gold and bismuth are monoisotopic. They make for clean beams. Hit 'em again! Harder! HARDER!!!

Anonymous said...

Hi,

I wonder, what is it that makes the quarks "comunicate" in this "liquid"?

macroscopic particles of the right size and density can be very helpfull when investigating the flow-properties of a liquid

But these particles ARE not the liquid.

- so, either there is a medium in which the quarks swimm, or there are forces between the quarks comunicating the positions among each other thus making it seem like they are swimming in a streaming liquid.

greetings

Klaus

Plato said...

IN regards to your post B

Bee said...

Hi Plato, it seems blogger is having some difficulties today.

In regards to your comment

To avoid doubling of information ;-)

Best, B.

stefan said...

Paul,

should be called Quark "GLUTON" ?

You mean like pluton ;-)
Otherwise I don't understand, I have to admit..

not really capture though, the fact that a new phase of matter at specific temperature, is an intermediate product?

Good point: The picture shows some static, equilibrium configuration, while a real collision is an extremely fast process - it takes only some Fermi/c, or the time for light to cross a large nucleus. It is not self-evident that it makes sense at all to speak of quark matter in equilibrium in connection with heavy ion collisions.

However, from models that analyse the collisions and interactions of partons (the quarks and gluons in the nuclei), it looks as if even this short time can be enough to create an equilibrated system, which then, of course, expands and cools extremely rapidly..

Virtual Gas = Virtual Solid = Virtual Liquids, for High temperatures, just as for Cold temperatures?

I guess I should write sometime something about the phase diagram of nuclear matter. So, indeed, the picture shows cool, compressed nuclear matter, rather than a hot quark gluon gas. Current wisdom ist that you can reach the QGP at moderate temperature also if you just compress enough. On the other hand, by heating, one goes through a cross-over form hadrons to a QGP, which means that there is a smooth change in the proprties of the particles, from hadrons to (maybe) QGP liquid to free QGP gas..

is the density of "Hot" Quark/Gluons, equal to that of "Cold" Quark/Gluons?

Here, one has to be careful about what is meant with density of quarks, since we deal with a highly relativistic system. In a hot QGP, the net density of quarks (quarks minus antiquarks) is very low, while the number density (quarks plus antiquarks) is very high, and comparable to the density of a cool, compressed QGP.

It is sure to note that a hot Plasma (phase of matter), can be of the same constituency of a cold Plasma (Bose_Einstein_Condensate) ?

I don't quite understand? Well, the same constituents, quarks and gluons, can form a "liquid" or gas at high temperture, and a "condensate" (Colour-Superconducitvity) at high density and moderate temperature.. OK, Colour-Superconductivity is, so far, not more than a theoretical prediction from QCD. It has never been observed yet, though lots of people are thinking about options to tune collision parameters such that it could be created, and about possible signals in the late hadronic data.


Best, stefan

stefan said...

Klaus,

I don't get the point with the need for the medium?

In a common liquid, there is no medium, it's just the particles, atoms or molecules, that make up the substance, which can move around, but have quite strong forces - either attraction, but short-range hard-sphere repulsion works also - among each other and, for that reason, have some short-range correlation.

It's the same here - one just has to stipulate that there are strong forces among the quarks, mediated by gluons, both attractive and reulsice, and sufficently high scattering cross sections.

Best, stefan

paul valletta said...

Stefan, just to clarify "GLUTON", I meant this to be relative to the process:

http://en.wikipedia.org/wiki/Gluten

Please forgive my bad choice of words !

Bee said...

Hi Stefan,

I think Paul might have made a pun, think GLUE, GLUONS, GLUTEN...

Best,

B.

Plato said...

IN regards to the stereo system, we have some amazing properties in our assessment of the WMAP

http://background.uchicago.edu/~whu/intermediate/basic1.gif

With the discovery of sound waves in the CMB, we have entered a new era of precision cosmology in which we can begin to talk with certainty about the origin of structure and the content of matter and energy in the universe.-Wayne Hu

So while the orchestration is quite pervasive in it's arrangement, there are wonderful songs going on in other locations within the CMB?:)

Afterglow is a nice song coming from a Canadian heart.

Plato said...

Principle of the Finite Imagination:How smart has the atom to be to imagine the existence of a human being? To imagine several billions of them? Of the world they live in? With all the global and sociological problems? How smart has the atom to be to imagine the existence of the earth, the solar system, our galaxy, the universe, or even multiverses? The poor atom was just looking for a theory of everything, just some few equations that extend the Standard Model such that they explain the observed liver growth.

From a cancer perspective the constituent as the atom may have had other issues to worry about since it had overtaken and caused a socialogical problem with the current status of life?

So unbeknownst to the wider perspective, the universe in ths explanation seem to have resulted in complex negoatatons, and it folowed a pattern in life?

So the ball rolls in which direction?

A cure for cancer. No hope?

Not likely to instill such things in the "fate of despair" when one askes for something to hold on too? Olli?

So it goes with AP? :)

SERHAT I┼×TIN said...

So far no problem (for me) in understanding that colour charge in bulk quark-gluon plasma is screened, yet what if one consider surface effects? What i mean here is actually plasma surface, no screened colour charge on surface or wtf ?? By the way I no I am a newbee physicist :p

serhat istin said...

So far no problem (for me) in understanding that colour charge in bulk quark-gluon plasma is screened, yet what if one consider surface effects? What i mean here is actually plasma surface, no screened colour charge on surface or wtf ?? By the way I no I am a newbee physicist :p

Gina said...

Wonderful thank you for this very informative blog.