Electron transportation

Dear experts,

I am using the Geant4.10.5p1.
I simulated simple electron simulation that the electron is generated from (0,0,0) to direction(0,0,-1) in pure water geometry, and checked the 1st step information.
I saw the x, and y position in postStep of electron have been not zero. I was confused because I thought that only z-direction have momentum so the x, y-position keep zero.
Is this the lateral displacement by multiple-scattering?

Best regards.

Yes. You should find that the momentum magnitude is also different, and that there is a non-zero TotalEnergyDeposit value (from dE/dx).

Thank you for your advice!
Is the non-zero Energy deposit comes from the true path length for the MSC theory?
I have another question about msc.
When I was using Geant4.10.3p2, these lateral displacement is not appeared in same simulation.
Both time I use EmLivermorePhysics.
Is this the version problem?

No. The non-zero energy deposit will come from (a) any continuous energy loss (dE/dx) computed for the path length by G4eIonisation, and (b) any energy deposit in the post-step discrete process which did not result in secondaries.

This sounds like a question for the EM experts. My naive response is that MSC always (necessarily) produces a lateral displacement. After all, it’s trying to emulate the random walk of multiple small scatters that a real particle would experience.

Thank you very much for the detailed explanation.
I know that is not realistic, but If I want to turn off the Lateral displacement, can I do it?

Sorry for repeating question.
But I am confusing about the difference of process name “msc” and “Cerenkov”.
I think “Cerenkov” process is represent to the Multiple scattering of Charged particle, and the true step length is same in both process.
Do you know where is the difference between both process?

Cerenkov refers to the process of emission of photons (in G4, specifically G4OpticalPhoton, not G4Gamma) when a particle traverses a transparent material with a speed higher than the speed of light in that material (c_eff = c/n, where n is the index of refraction). It is implemented as a discrete (single interaction at a time), not continuous process in G4.

Thank you very much!
I am very sorry for lack information.
The situation I read the process is below, (here, the theStep is the variable of the G4Step class )

thePostPoint = theStep->GetPostStepPoint();
theProcess = thePostPoint->GetProcessDefinedStep();
process_name = theProcess->GetProcessName();

These are written in the SteppingAction function.
Then, the process_name is “Cerenkov”, “msc”, “eIoni”, and so on.
Technically, I think the “Cerenkov” means the step is limited by step length, which is calculated by the MSC method.
If so, what is the “msc”? (That is my actual question).
I checked the true step length, it with msc is very shorter than it with Cerenkov process.