I guess that this is the desintegration of a muon into an electron (much likely a positon because the decay of negative muon is more complicated ). This video comes from    • Natural radiation in a cloud chamber   at 24:44 seconds.
At A, the muon is coming up to down and reach the point B where it encounter a nucleus (electrostatic collision) which deflect it a bit to the point C. The path B to C is erratic, this not a straight line like A to B, because during the collision, the muon lose a lot of its kinetic energy. It come at rest at C where it decay into an electron and a neutrino. But due to the large rest mass of the muon (105 MeV/c²), a lot of energy is shared between this last 2 particles. After the decay of the muon, the electron can get from 0 to 70 MeV of kinetic energy, but on average, it's 35 MeV and the rest for the neutrino.

What are we observing ? this is indeed the case. The track C-D is an electron with a very big energy as it's a straight line, showing no disturbance (deflection). At 35 MeV, the range in air is about 100 meters.

How are we sure it can be the disintegration of muon, and not the backscattering of a particle coming from D to C with a collision at C ? because after this process, it's very unlikely that the line B - A would be straight. It should be erratic, with a lot of deflection due to Coulomb interaction as the particle have literaly no kinetic energy left. So the initial particle, is coming from A.

How can we prove that ? with historic pictures. Take a look at :
https://www.cloudylabs.fr/wp/interact...
and see how the electron is emmited like a straight line in the end of the muon track.


I'm happy about this.