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S30XL-LESA/LDMX
With calibration enabled, some channels show a non-Gaussian distribution of noise - the sampled ADC value splits into "upper" and "lower" peaks.
Some channels are affected more than others - some dependence on cal group, but varies widely within a group. This is the average RMS value of every sample for a given channel:
We cut on the second sample of channel 32 being above or below a threshold. We see that other samples and other channels get cut in the same way (including channels not being calibrated), so the noise is common to all channels.
Without cut:
Events with sample below threshold:
Events with sample above threshold:
With CSEL set to give no calibration pulses, we still see this effect:
The sequence of "upper" and "lower" events appears to be random.
If one channel group is being calibrated, other channels see crosstalk at ~1/10 amplitude, opposite polarity. This is visible in the plots above.