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Time fix #119

merged 4 commits into from Oct 27, 2020

Time fix #119

merged 4 commits into from Oct 27, 2020


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@mroda88 mroda88 commented Oct 14, 2020

This pull request assigns proper space and time coordinates from Pythia decayed particles according to our new definitions: space in fm and time in ys.
I took the liberty to have some optimisations and I changed the unit definitions from static const to static constepxr so the scaling factors could be defined as constexpr. This trick could be done with constants as well but it was beyond the scope of this fixes and I will defer to a later moment.

About the validation tests. I generated tau events, enabling the pythia decay for tau. The taus were generated on protons, with a uniform flux up to 35 GeV.
With a macro (available in $GENIE/contrib/pythia_units) I extracted time of flight and decay length for the taus and I plotted them.
As you can see the length goes up to 18 X 10^12. Being this in fm, this corresponds to a maximum of 1.8 cm which is expected from the typical OPERA experience.

To understand the time unit, I fitted the points.
Screenshot from 2020-10-14 12-46-18
The slope is about 0.3 fm / x and it is supposed to be the speed of the tau, which is heavily boosted so, close to the speed of light ( about 3 X 10^8 m/s ). Solving for x, that is 10 ^-24 s as expected. So the time is in ys.

Let me know if we need more.

@mroda88 mroda88 added the framework Framework related issues or improvements label Oct 14, 2020
@mroda88 mroda88 added this to the 3.2.0 release milestone Oct 14, 2020
@mroda88 mroda88 requested review from candreop and nusense Oct 14, 2020
@mroda88 mroda88 self-assigned this Oct 14, 2020
@mroda88 mroda88 merged commit 8b7fff0 into master Oct 27, 2020
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