Based on this study, I would recommend that the code in makePhotonPatch.c be changed as follows to agree with Eq. 3.
------------------------------ #define TARGET_TO_LGD_DISTANCE 102.9 #define LGD_RADIATION_LENGTH 3.1 #define LGD_SHOWER_OFFSET 2.35 #define E_CRITICAL 0.01455 ... zMax = LGD_RADIATION_LENGTH*(LGD_SHOWER_OFFSET + log(cluster->energy/E_CRITICAL)); ------------------------------
As a check, I applied this change to the code and then generated a sample of 10000 showers from gamma rays at normal incidence and random energies between 0 and 2GeV. For each shower I compare the actual depth centroid returned by the generator with the value of zMax computed by makePhotonPatch. The comparison is shown in Fig. 5.