Light simulation issue 4: Reproducibility

[YifanC]

In my naive understanding, the randomness of the light simulation only comes from the detector noise. However, I am seeing some reproduciblility issues when looking for signals (any peaks). In general, the signals are around the same time and around the same channels with some variation. Taking one channel (ch 150) from simulating the second event of MiniRun5_1E19_RHC.convert2h5.00666.EDEPSIM.hdf5 as an example. The seed is not fixed but I don't think it affect it here...(will test again with fixed seed). Four repeats yield quite different results.

Tag @mjkramer @krwood @liviocali @AWh1t3 for comments

[liviocali]

There is a randomness in the light simulation: The for the number of photons we apply a poisson smearing based on the calculated incidence. See

larnd-sim/larndsim/light_sim.py

Line 232 in 57d1e09

def calc_stat_fluctuations(light_sample_inc, light_sample_inc_disc, rng_states):

[AWh1t3]

Is it a little weird, Livio, that one of Yifan's events has no peak at all? I understand we want poisson fluctuations for the number of PE per time tick, but that one just looks like the light was completely deleted.

[krwood]

In principle, the random number from the poisson sample should be reproducible if we fix the seed. This was also observed not to be the case in the charge simulation, as in Issue #125

[YifanC]

Will test with fixed seed