Muon pair production from bremsstrahlung photons - optimisation

Physics, Transport and Magnetic Fields
1

I am simulating muon pair production from a 20 GeV e- beam incident on a tungsten target.
Currently it is taking over 2 hrs (1 core) to run 1e5 electrons.
I have implemented PART-THR and EMFCUF, but they don’t seem to be helping.

I am cutting bremsstrahlung photons < 211 MeV and electrons below 211 MeV.

The input file is attached. I have tried a number of things but nothing seems to be making it more efficient. Any insights would be very helpful.

muon_prod.inp (1.2 KB)

2

Dear Joshua,

there are a few issues with your input:

  • The PART-THR card only sets the energy transport cutoffs for hadrons, muons and neutrinos.
  • You need to specify the region on the EMF-CUT card with Type transport, otherwise it is only applied to the second region.
  • You should add a second EMF-CUT card with Type PROD-CUT to prevent the generation of electrons and photons below the energy limit for the specified material.
  • Finally, on the EMF-CUT card you specify 200 GeV instead of 200 MeV.

Cheers,
David

3

Hi David,

Thanks for the help. I have it running now with precision physics and the recommended EMFCUTs and it takes about 30 min for 1e7 primaries. That’s fast enough for me.

My last question: I am not seeing any muon pair production occurring yet, it seems from the documentation that precision physics automatically includes bremsstrahlung and muon photonuclear pair production. Is this correct? Perhaps the muphoton card I added isn’t doing what I hoped.

-Josh

muon_prod.inp (1.2 KB)

4

Muon pair production by photons is not activated by any default choice, rather requires a PHOTONUC card with SDUM=MUMUPAIR.

Although your MUPHOTON card has no effect being empty, muon photonuclear reactions are indeed activated by default. However, these concern the muon interaction with atomic nuclei via virtual photon exchange, not the muon pair production by high-energy photons discussed above.