# Asymptotic Freedom - Qualitative Explanation

I am doing a (mostly qualitative) course on Particle Physics, and am confused about the concept of asymptotic freedom. The lecture notes basically say that a quark may experience no force/be "unbound" temporarily as a result of a collision. (due to properties of the strong force) Is there all there is to it?

Later, it mentioned that asymptotic freedom is important in electron-positron annihilation into hadrons. Were there no asymptotic freedom, the cross section of the process would be different. I can't see how this follows on from what was said above.

So I am seeking an qualitative explanation of this concept, and perhaps something about its consequences as well.

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From the horse's mouth -- frankwilczek.com/Wilczek_Easy_Pieces/373_Asymptotic_Freedom.pdf (Wilczek was one of the Nobel prize winners, for a theoretical understanding of asymptotic freedom). –  Siva May 16 '13 at 7:27
possible duplicate of physics.stackexchange.com/q/45514 –  John Rennie May 16 '13 at 9:05
If you like this question you may also enjoy reading this Phys.SE post. –  Qmechanic May 16 '13 at 14:10
@JohnRennie no, the question you linke to is not a duplicate. Asymptotic freedom and confinedment are NOT the same. There is absolutely no reason to close this question, as some people think. –  Dilaton May 18 '13 at 19:42

In order to understand asymptotic freedom, you need to be aware of the concept of renormalization. Since you want a qualitative description, just think of renormalization a modification of the coupling strengths and masses of particles at high energies. This is roughly like pushing a ball through the water; the harder you push, the more the water sticks around it and the harder it is to move. This can be modeled with Newton's 2nd law $F=ma$ by replacing the mass with a slightly larger mass $m+\delta m$, and this $\delta m$ depends on the velocity of the ball in the water.