S1 scintillation timing from NEST

[terliuk]

What is the problem / what does the code in this PR do
Introduces new mode for S1 shape where timing is done from timing spline, and scintillation time is received directly from nestpy which will address issue #165

[terliuk]

here is the example of running it : https://github.com/XENONnT/analysiscode/blob/master/s1_pulse_shape/S1_WFsim_pulse_shape_NEST_example.ipynb
One more comment - we might need to re-adjust epix instruction handling, as we need excitons, number of emitted photons and local field at the point of the energy deposit. @ramirezdiego has some ideas there, so likely we will make a "tandem" PR for both epix and wfsim.

[skazama]

Hi @terliuk, I cannot comment about epix, but I had a look at your code and it looks fine. Also I managed to run the notebook with your branch and could generate Kr83m S1 signals without errors, so maybe we can merge this? (or do we have to wait for @ramirezdiego's ideas?)

[ramirezdiego]

Hi @skazama. The code works fine indeed (thanks for jumping in!), but in a recent chat with @terliuk I suggested that it would be better to push the relevant changes to epix before merging this PR; i.e., to output the required information in the instructions (efield, number of excitons...).

This requires to change the instructions format also in WFSim: either by adding another one, with these extra columns, or adding the columns to the default one, but make epix always print out some dummy number for them. In case this wasn't clear: epix reads the format directly from WFSim: https://github.com/XENONnT/epix/blob/43e7e31a05d0ff52863c2017f367bff7eb859312/epix/io.py#L202 This would be the missing part of this PR.

Edit: I had missed the last comment by @terliuk, sorry. But okay, we seem to agree on pushing the epix fix at the same time/right before.

[terliuk]

after recent changes, i need to do extensive testing again, confirming that it works as intended