# Why quarks are confined? Why can't they be found in unbound states?

No one has observed before a "free" quark, i.e. a quark in an unbound state. According to one paper, I read that $$p\bar{p}$$ collision produce unbound $$t\bar{t}$$ pair which quickly decay into other particles. But some people argue that the produced $$t\bar{t}$$ pairs decay so quickly that they had no time to bind! And I agree with this idea.

So why can one not find quarks in unbound states?

This is because the force-versus-distance law for quarks is such that the farther away from one another you pull a pair of quarks, the harder they attract one another. It is as if they were attached to each other with a rubber band (a very stiff one!). If you pull them far enough apart, there's enough energy stored in the system to create a new pair of quarks (i.e., the rubber band snaps) which pair up with the others and instead of getting two "free" quarks, you get a pair of mesons with two quarks inside each one.

If you want a more descriptive and a simple mathematical treatment using the formulation of electrodynamics and quantum mechanics, then Leonard Susskind's series of lectures will give you a lot of insights!!

Here is the Link : https://inspirehep.net/literature/1532

Quarks that are lighter than the QCD scale, ($$\sim 200\,{\rm MeV}$$) will always be confined, but heavier ones can be unbound. The top quark weighs $$170\,{\rm GeV}$$, so it can be unbound.

The QCD scale is the mass scale that pops out when you renormalize the strong interactions.