Muon Interactions

Muons, being charged particles (mu+ and mu-), can interact with matter by ionizing it. They themselves lose energy during this process.

Stopping power

The stopping power of a material to a particle is defined as the energy loss in a unit track length, S = -dE/dx. It changes with material, particle type, and the kinetic energy of the particle. The first figure in the [PDG][] [review][] on Passage of particles through matter shows the dE/dx of muons in Cu as a function of their energies. It reaches its minimum around 1 GeV.

Cosmic ray muons

According to [HyperPhysics][], the average energy of muons reaching sea level is about 4 GeV. They are called [minimum ionizing particles][mip], as their dE/dx in air is around its minimum . A muon loses about 2 GeV passing through the atmosphere, its original energy is then about 6 GeV.

Both mu+ and mu- can be created in the air by protons from the Sun. The ratio of (number of mu+)/(number of mu-) is around 1.3 according to http://arxiv.org/abs/1005.5332. The momentum and angular distributions of cosmic ray muons at sea level can be found in https://arxiv.org/abs/nucl-ex/0601019.