Dear contact,

I have two questions regarding sampling cutoff for ionization energy loss of particles where the Landau function is used as a probability density function.

- Is the Landau function used when simulating energy loss fluctuation (straggling)?

In the GEANT3 manual (CERN Program Library Long Writeup W5013), the “PHYS332” starting from page 258 explains that Landau function is used with cutoff coming from fitted function for \lambda_max introduced in page 261.

In GEANT4 physics reference manual (Release 11.1), only Urban’s model is introduced in 7.3.2 at page 75. Does it mean that GEANT4 uses Urban model for thin absorber case regardless of delta ray production above a given threshold energy?

- If Landau function is still being used, is the same \lambda_max function introduced in “PHYS332” of “CERN Program Library Long Writeup W5013” used for sampling cutoff?

In this case, I revisited it using TMath class of the ROOT and observed that the parameters of \lambda_max function in “PHYS332” is valid only for lower lambda values. If the same function is used, cutoff for higher lambda values are low. Please refer to “https://github.com/sungbinoh/Landau_cutoff_for_mean/blob/main/lambda_max_formula_comparison.pdf”.

Thanks in advance for your help.

Best regards,

Sungbin.