Pedestal and Common Noise in the test beam data Rudi Ganz  October 20th 1997

Here are some pictures generated from file #RUN00100.dat from the 1997 test beam data. Here is for the WA98 detector segment number #1    ADC value versus channel number for the telescope detector 1 click here:  

before the subtraction of pedestals*	after subtraction

( *generated as channel by channel average over the "pedestal tagged" events)

The question now is whether there is common noise which we then have to subtract on an event-by event basis. Common Noise means a correlated change of the pedestal. So if one plots one the ADC value of one channel against the other channel (in the same Read-Out chip) one can look for such correlation's:

The histograms (as suggested by Russell) show the correlation of the noise between each channel of one readout chip  with all the others. (So I take the first channel on the chip and plot it against channel 2-128; then I take second channel and plot it against 3-128 and so on ...) Each WA98 detector is read out by 8  128 channel VA chips.
     

chip 1	chip 2	chip 3
chip 4	chip 5	chip 6
chip 7	chip 8

  One can see also no significant correlation in the WA98 detector(may a small hint of it) -> no significant common mode noise.