How do collisions between cosmic ray nuclei and interstellar hydrogen produce pions?

When primary cosmic ray atomic nuclei collide with interstellar hydrogen, the high-energy interaction results in the production of mesons, specifically pions.1

These pions are categorized by their charge and decay through different processes:

• Charged pions: These particles have a very short half-life of approximately two hundred-millionths of a second. They decay into muons, which subsequently decay to produce electrons, positrons, and neutrinos.1
• Neutral pions: These particles decay rapidly into high-energy gamma rays.1

The detection of these resulting gamma rays and the synchrotron radiation generated by the secondary electrons provides critical evidence for the distribution of cosmic rays within the Milky Way Galaxy.1