alcap-org / g4sim

Simulation toolkit based on Geant4 and ROOT
http://wuchen1106.github.io/g4sim/
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Is MomSpread specified in the input configure file the FWHM or the sigma? #42

Closed AndrewEdmonds11 closed 9 years ago

AndrewEdmonds11 commented 9 years ago

The sigma.

In the PrimaryGeneratorAction here, it uses G4RandGauss::shoot(0,MomSpread), which is just the CLHEP::RandGaussQ::shoot. This function takes the standard deviation (sigma) as the second argument so that is how we are using momentum spread.

Nam said that the 3% momentum spread that we were using during the run was the FWHM so we need to convert it at some stage (see here for a definition).

Should we do this in the code itself or shall we just change our momentum spreads in the configure files? I guess it doesn't really matter but we should just make sure we all use the same thing.

thnam commented 9 years ago

I think specifying in the config files is easier. I have made several config files in this commit: bd7b7a597426cfcf895cf3420c15c0a39c0e2397.

A look-up table is at the bottom of those files: Scale Momentum Spread Energy
1.03 28.84 0.368 3.865
1.04 29.12 0.372 3.939
1.05 29.40 0.375 4.014
1.06 29.68 0.379 4.089
1.07 29.96 0.382 4.166
1.08 30.24 0.386 4.242
1.09 30.52 0.390 4.320
1.10 30.80 0.393 4.398
1.12 31.36 0.400 4.556
1.15 32.20 0.411 4.798
1.20 33.60 0.429 5.214
1.25 35.00 0.447 5.646
1.30 36.40 0.465 6.094
1.35 37.80 0.483 6.558
1.40 39.20 0.500 7.037
1.43 40.04 0.511 7.332
1.45 40.60 0.518 7.532
1.47 41.16 0.525 7.734
1.50 42.00 0.536 8.042
1.60 44.80 0.572 9.105

Why doesn't it show as a table ...

AndrewEdmonds11 commented 9 years ago

I think specifying in the config files is easier.

I agree.

Thanks, Nam for resolving this with the table.