The title sums everything up. The fusion cross section increases up to a certain temperature due to collisions and the increased probability of tunneling through the coulomb barrier. But why does the cross section drop after a certain number? Do the collisions become less frequent or is there any other reason behind this? My friend told me, once the particles start moving extremely fast, they don't have enough time to fuse (for tunneling to make them fuse). Is this right? If it is, what is the minimum time needed for the particles to fuse?
- Why do the cross sections drop after a certain temperature?