# 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.

• 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
Commented May 16, 2013 at 7:27
• possible duplicate of physics.stackexchange.com/q/45514 Commented May 16, 2013 at 9:05
• If you like this question you may also enjoy reading this Phys.SE post. Commented May 16, 2013 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. Commented May 18, 2013 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.