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, 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.

Scintillating panels

panels.tg contains a portion of a plastic scintillation panel. panels.mac shoots 6 GeV mu+ to it. The simulation result is saved in a ROOT file panels.root.

dE/dx plot

The GEARS output provides two variables to roughly calculate this: de and dl. de is the energy deposited in a step point. dl is the corresponding step length. A jupyter notebook dedx.ipynb is created to analyze the cosmic ray muon dE/dx in air and the scintillation panels. It can be run in a web browser through binder or Google CoLab.