Geant4 step size

Hello, I simulated a 45GeV e+ , here the features of the beam

/gps/particle e+
/gps/energy 45 GeV
/gps/ene/type Gauss
/gps/ene/sigma 0 GeV
/gps/pos/type Beam
/gps/pos/shape Circle
/gps/pos/radius 0. mm
    /gps/pos/sigma_x 0.3 mm
    /gps/pos/sigma_y 0.3 mm
    /gps/pos/centre 0 0 -100 cm 
    /gps/direction 0 0 1

then you see…it’s a gaussian beam having a sigma_x and sigma_y 300um. The beam hit 2 targets… I’m studying the positrons outgoing the targets…

This is a plot of the positrons outgoing the first target (it’s a Be target having hourglass shape and the thickness at the center of the hourglass is 3mm)


On the x axis I plotted
x=x_ext-x_prod where x_ext is the position at the exit of the target and x_prod is the position of production of the primary positron

On the y-axis I plotted x' that is the angle at the exit of the target.

You see there is a long line at x=0, as if x_ext=x_prod… my supervisor said me that he thinks that it’s due to the step dimension…then to try to modify the step size…but…how to modify it?
I’ve the and StepMax.hh but I can’t find a value to modify

StepMax.hh (3.0 KB) StepMaxMessenger.hh (2.5 KB) (3.6 KB) (3.0 KB)

Hello anyone please?
Ps. I forgot…this is the ROOT macro to plot data and here the full source of the simulation I run the simulation using run1.mac