How to change the physics model of msc

Physics Processes, Models and Cross Sections
1

Dear experts,

I am a rookie of Geant4. Thank you for the helps in advance.

I am working on the scattering angle study.
I saw a plot (Figure 1 of ShieldSquare Captcha) that changes the physics model (Stand EMV, WVI-MSc, Single Scat, etc.).

Question 1 : Can you please give an introduction about how to actually implement it (change the model of msc) ? I want to try the model “WVI-Msc” and Single scattering.

The purpose of this is because that we have a project that the result of data doesn’t agree with the MC, as shown in “Scattering angle comparison.png”.

Scattering angle comparison
Scattering angle comparison1920×947 97.1 KB

Currently the Physics list I used is “FTFP_BERT”. We also tried with the “FTFP_BERT_EMZ”, but no significant difference, the agreement between data and MC is still poor. Therefore I think I should try to change the model of MSC (multiple scattering).

======================== Some information about our experiment : ===================
BeamTest experiment with silicon tracker in ELPH, Japan. The positron beam with the energy of around 950 MeV was used in the experiment.

========================== Some information about the MC : =======================

  1. The experiment setup was almost included in the MC (scintillators, readout board, glue, mechanical support, etc.).

  2. The positron beam was used in the MC

  3. The informations of the beam energy distribution and the beam direction distribution is provided by the accelerator group (ELPH), should be precise enough.

  4. The physics list of “FTFP_BERT (_EMZ)” was used.

  5. In the run.mac, the following was added.
    /run/setCut 1 mm
    /run/setCutForAGivenParticle e- 0.1 mm (also tried with 0.08 mm)
    /run/setCutForAGivenParticle e+ 0.2 mm (also tried with 0.08 mm)
    /run/setCutForAGivenParticle gamma 0.3 mm (also tried with 0.08 mm)

Question 2 : Or is the direction I think incorrect ? (has the scattering angle distribution of positron at that given energy range already been fully understood ? If the answer is yes, then probably the problem is from my side, maybe the geometry of my G4 setup has to be optimized.) But I also found a paper (Year : 2014. Title : Multiple Coulomb Scattering in Thin Silicon. Link : https://arxiv.org/pdf/1405.2759.pdf), which shows a discrepancy between data and MC in the study of the scattering angle distribution.

Question 3 : Or is there any suggested physics_list I can try for such energy range ?

Thank you again !
Happy holidays !

2

Hello,

you describe everything except beam energy.

The approach you described in details is correct but absence of tails in scattering angle for me is strange. From my point of view, your choice of physics is optimal.

VI

3

Hello VI,

Thanks for the reply.
In the experiment, the positron beam with the energy of around 800 MeV was used.

I found that the “_EMZ” doesn’t take the Single Coulomb into account. So I also tried with “_WVI” and “_SS”, but the agreement doesn’t improve.

There is a paper I found (Year : 2014. Title : Multiple Coulomb Scattering in Thin Silicon. Link : https://arxiv.org/pdf/1405.2759.pdf), which shows a discrepancy between data and MC in the study of the scattering angle distribution in thin silicon.

I wonder was the physics model in large angle scattering tuned already ?

Thank you
Best,
Cheng-Wei