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DIS weights in 2.12.10 do not conserve total cross section. #2

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jonpaley opened this issue Oct 2, 2018 · 2 comments
Open

DIS weights in 2.12.10 do not conserve total cross section. #2

jonpaley opened this issue Oct 2, 2018 · 2 comments

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@jonpaley
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jonpaley commented Oct 2, 2018

We have discovered that the DIS-related weights in v2.12.10 do not conserve total cross section. We see this when we apply, eg, the GENIE formation zone weights to an analysis that is very sensitive to DIS events (neutrino energies > 10 GeV) in the NOvA far detector. In short, if we apply absolutely no event selection in the analysis, and look at the predicted far detector true neutrino energy spectrum (with no extrapolation using the near detector), this weight moves the event rate up and down. But the formation zone should have no impact on the actual cross section, and only just impact the distributions of the final-state hadrons. We have confirmed that the average formation zone weight is not equal to 1. We have seen similar effects for other DIS knobs.

Can this be fixed in GENIE v3?

@candreop
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candreop commented Oct 4, 2018

The issue with the formation zone is likely to be a inherent limitation of reweighting that cannot be fixed. Tweaking parameters might open up the space of likely event generation outcomes, but you cannot reweight events that were not generated in the first place. With the formation zone, the presence of the nucleus boundary plays a role and when a particle escape the nucleus then the game is over. If the full ensemble of events needed to balance out weights (for any systematic that is meant to maintain unitarity) is not available then the average weight will not be 1. This is only one of the unavoidable reweighting limitations that led GENIE tuning to produce weighting functions from brute force scans via Professor. Will investigate the issue but it is unlikely this will happen before v3.0.0 release.

@jonpaley
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jonpaley commented Oct 4, 2018

Thanks for getting back to me Costas, and for clarifying the specific issue with the formation zone. I think a disclaimer about this is needed in the GENIE manual, because this will require a different treatment than how experiments treat other GENIE knobs.

However, we also saw this same problem with other DIS-related knobs, examples are the pi pi- and N pi-production probabilities. So is this a general feature of all hadron transport "knobs"?

ShiveshM pushed a commit to ShiveshM/Generator that referenced this issue Dec 14, 2018
Corrected implementation and inferfaces for Delta decay
idkakorin added a commit that referenced this issue Mar 18, 2019
idkakorin added a commit that referenced this issue Mar 18, 2019
Merge pull request #2 from GENIE-MC/master
mroda88 added a commit that referenced this issue Dec 2, 2019
candreop added a commit that referenced this issue Feb 28, 2020
sync candreop and GENIE-MC Generator masters
mroda88 pushed a commit that referenced this issue Nov 9, 2020
sync with GENIE-MC master
afropapp13 pushed a commit to afropapp13/Generator that referenced this issue Mar 11, 2021
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