Dear Yuri,
I found you note on the BB counters very informative and the data very
exciting. However I think that there is a small problem with the extraction of the ADC gain and
multiplicity related to your use of the Pedestal RMS in section 1.1
You define the gain AdcGain0 as the first peak in the distribution of
ADC - Ped - 2*PedRMS Eqn 1
and then you define as
MultPerTube = <ADC - Ped - 2*PedRMS>/AdcGain0 Eqn 2
where < > denotes an average over a given class of events.
Let us say we have a tube whose ADC spectrum shows 4 peaks corresponding to the
Pedestal at 50
1 MIP at 80
2 MIPS at 110 and
3 MIPS at 140
Then suppose that PedRMS = 10. (This is extreem but bear with me)
Eqn 1 gives AdcGain0 = 80 - 50 - 2*10 = 10.
Then for a given event if say you have an ADC value of 80 corresponding to 1 MIP then
Eqn 2 implies
MultPerTube = (80 - 50 -20)/10 = 1 which is correct.
However if for the next event ADC = 110 (ie 2 MIPs)
MultPerTube = (110 - 50 -20)/10 = 4 which is incorrect.
The problem is even worse for higher values. If ADC = 140 (ie 3 MIPS)
MultPerTube = (140 - 50 -20)/10 = 7
Of course the magnitude of the problem is probably much smaller in your analysis since the
width of the pedestal is probably a small fraction of the distance between peaks.
The problem can be corrected by not plotting ADC - Ped - 2*PedRMS but simply
ADC and looking for the first peak above Ped+2*PedRMS and calling this AdcGain1
Then
MultPerTube = <ADC - Ped>/AdcGain1 Eqn 3
I beleive that this will lead to more correct and lower dN/dEta values.
Yours Michael
:
: Michael Murray murray@comp.tamu.edu
: Cyclotron Institute, Texas A&M University, TX 77843-3366
: Telephone (979) 845 1411, FAX 1899
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