Cosmic Ray Muon Production Altitude is not right!! Hi there, I wrote a Programm to calculate the cosmic ray muon intensity on different altitudes. I dedicated this programm from the intensity of the primary cosmic rays and the intercations in the atmosphere. First a Proton with the Energy E1 enters the atmosphere and after the mean interaction lenght after 18km above sea level collides with a Proton of an atomic nucleus which is not in motion. For a pp collision like that the center of mass energy is given by: Sqrt(s) = Sqrt(2 * E1 *mp) Where mp is the mass of the Proton of the nucleus. This collision produces +/- and 0 Pions each one 33%, the number of Pions produced can be read out of a plot from Review on Particle Physics (see attachment) and depends on the cms Energy. The kinetic Energy of the Produced particle can be calculated by: Ekin=(Sqrt(s)-N*m)/N where N is the number of Pions produced and m the mass of a Pion. Using the same algorithm I can calculate the other collisions in the atmosphere, now between Pions +/- and nuclear Protons. The altitudes of such collisions would be 12 km, then 9 km then 7.7km, calculated with the mean interaction lenght. The Problem is the pions do not reach the second collision because of decaying in to muons. The result up to Energies of the primary Proton of 100TeV all the pions decay at about 14 to 12.5km altitude in Muons. In fact this is different we do have certain energetic Pions wich decay on 7km altitude. Why could my programm fail in calculating the muon production altitude? Can you help me?