ADC width & mean vs. LED amplitude for subSector 6TC
Data taking: (eLog #506)
- pulse LED for 6TC
- change LED amplitude ( 2000, 2200, 2600, and 2800) and take 4.7K events (runs 216, 245,246,247)
- find mean & RMS for pedestal subtracted spectra
- plot RMS^2 vs, mean for every tower and fit Y(x)=a +b*x
name a b
# Tw01 -3.458853 0.250347
# Tw02 -3.945185 0.289377
# Tw03 -9.538951 0.359066
# Tw04 -6.344077 0.413668
# Tw05 -5.859556 0.410653
# Tw06 -27.151926 0.537919
# Tw07 -13.252053 0.456244
# Tw08 -14.410488 0.541332
# Tw10 -49.165291 0.782155
# Tw11 -24.407122 0.522069
# Tw12 -47.135193 0.647071
Some observations:
formula Y(x)=a +b*x , describes the case of RMS=sqrt( alpha* Nphotons + beta*LEDwidth^2). It works reasonable (with LEDwidth~0) for towers with a low measured ADC, but fails for the towers with large ADC.
a possible explanation: LED pulese width gets wider with increasing amplitude.
(I gave up after 3 hours an attempt to fit of both alpha & beta simultaneously).
This is 'quick & dirty'. Do not pay attention to chi2 nor to errors of fit params, since
the following errors were assumed. (I do not know what ROOT does with 'err_X'?)
float y=rms*rms;
float ex=rms/sqrt(4700);
float ey=2*ex;
gr->SetPoint(n,mean,y);
gr->SetPointError(n,ex,ey);
(.ps)
The data point are here , in case someone wants to play . The .C script.