I scattered 10 GeV muons off lead with different thicknesses (1 to 30 mm). I am looking for scattered muons with transverse momentum bigger than 200 MeV/c or 250 MeV/c resp.. For a "defaultCutValue" of 1 mm, i get a non linear rate as a function of the thickness of the lead. Decreasing the "defaultCutValue" the rate becomes more and more linear, which is fine. But the rate becomes smaller and smaller, the higher the Cut Value is; much below the experimental values. Due to single muon scattering the behaviour should be linear for large angles (large transverse momentum), but why is the rate so sensitive to the Cut Values? Why does the rate not converge for small Cut Values?
With low production threshold, the emission of d-rays and bremsstrahlung in the absorber guarantees several steps. With high cut, there is only 1 step, and the multiple scattering occurs only once, when the particle exits the absorber. Then the tail of the theta distribution is contreversal. There is a way to force a stepMax 'by hand', in order to have several steps in the absorber, via G4UserLimits. I ran few test jobs with a program derived from our examples/extended/electromagnetic. I attach the code and the results.txt : when using a stepMax, the results are more stable against the production cuts. It is foreseen to implement an algorithm to force the multiple scattering to do automatically at least few steps in any layers. But this is still under study.
