Gross, Politzer & Wilczek: 2004 Nobel Prize Winners in Physics

[marcus]

David J. Gross, H. David Politzer and Frank Wilczek are awarded the 2004 Nobel Prize in Physics

 

[humanino]

you're late
[thread=46198]arivero[/thread]
I am so glad about this prize !
QCD rules

 

[marlon]

you're late
[thread=46198]arivero[/thread]
I am so glad about this prize !
QCD rules

Since i did my master-thesis on this subject, i can only agree with those wise words of Humanino : QCD rules...

marlon

 

[marcus]

a brief sketch of asymptotic freedom

Sean Carroll gave a simple sketch of the main idea (not for marlon and others for whom it is an old story, but for any newcomers)

"...CD is the theory of the strong interactions, in which quarks possesses a certain "color" (purely metaphorical, of course) and are bound together in protons and neutrons by massless particles called gluons. It's extremely similar to how protons and electrons possesses a quantity called "charge" and are bound together in an atom by photons. But there is also a crucial difference -- you can pull an electron apart from an atom (and thank goodness, since TV and other necessities would otherwise be impossible), but you can't pull quarks out of protons and neutrons. The basic reason why is asymptotic freedom -- the remarkable quality that the QCD force gets weaker at higher energies (short distances) and stronger at low energies (large distances). In the early '70s physicists were struggling to understand new data on the structure of protons and neutrons from "deep inelastic scattering" experiments at the Stanford Linear Accelerator (SLAC) and elsewhere, in which high-energy electrons were fired at these heavier nuclear particles. It all snapped into place once Gross, Politzer and Wilczek discovered asymptotic freedom (through some heroic calculations) and immediately applied it to make sense of the data -- the quarks were becoming free (non-interacting) asymptotically (as the energies were increased). Bjorken and others had discussed the possibility of asymptotic freedom, but it was Gross, Politzer and Wilczek who actually demonstrated that QCD (a non-abelian Yang-Mills theory, to be specific) would have that property. These days QCD is a phenomenally successful theory, and forms a crucial part of the Standard Model of particle physics. This is a Nobel Prize that is long overdue and well deserved..."

http://preposterousuniverse.blogspot.com/2004/10/nobel-prize-in-physics-for-asymptotic.html

 

[marlon]

As an addendum to marcus's post...

Three quarks bound together is a baryon. Examples are the neutron and proton. A quark-antiquark-combination is called a meson like the pion , which is the lightest meson ("easiest to make, if you will").

The quarks in baryons and mesons are held together by the strong force which is mediated by the gluons. These are elementary massless particles. The different baryons in the atomic nucleus are held together by the residual strong force mediated by the pions (they are not elementary particles).

The biggest difference between photons and gluons is the fact that gluons carry colour-charge and they can interact with each other as a consequence of this. Photons do not interact whiwh each other...

Photons also do not interact with the Higgs-field because the U(1) symmetry always remains after the spontaneous breakdown of symmetry. So basically photons are always massless particles.

regards
marlon

 

[Haelfix]

The calculation I think they are referring to is the pinning down of the QCD beta function exactly.

An extraordinarily hard thing to do if you don't know anything about dimensional regularization, like they do in classrooms in field theory. What takes 3 lectures to describe nowdays, would take (given the technology of the time) something like 50 lectures.