1. Gain Curves Continued Peter Litchfield Phone Meeting 29 th September 2005 Previously:  Some LEDs gave ~linear PMT v PIN ADC curves  Some didn’t  Same PMT is linear with low gain PIN and non-linear with high gain and vice versa.  PIN problem  How prevalent is it? High gain PIN PMT ADC Residual PIN ADC

2. Procedure  Fit Gain curve with a straight line passing through (0,0) between 0 and 8000 PMT ADCs  Corrected for zeros  Avoids most of the saturation non-linearities  Require at least 5 points in this range (significant number of near strip ends fail)  Calculate the  2 divided by number of data points for the straight line fit.  Plot for all the strip ends (~600) fed by each led  Calculate mean  2 /NDP for each LED

3. PB2 LED 20  2 /#data points of linear fit High PIN Near PMT Mean=4.2 High PIN Far PMT Mean=2.4 Low PIN Near PMT Mean=2.3 Low PIN Far PMT Mean=2.0 NOTE DIFFERENT HORIZONTAL SCALES  Linear fit OK  Near PMT a little worse than far, saturation effects?

4. PB2 LED 9 High PIN Near PMT Mean=2.2 High PIN Far PMT Mean=1.5 Low PIN Near PMT Mean=57.3 Low PIN Far PMT Mean=70.1 NOTE DIFFERENT HORIZONTAL SCALES  High gain PIN OK  Low gain PIN otherwise

5. PB2 LED 8 High PIN Near PMT Mean=110.9 High PIN Far PMT Mean=147.4 Low PIN Near PMT Mean=3.5 Low PIN Far PMT Mean=2.6 NOTE DIFFERENT HORIZONTAL SCALES  Low gain PIN OK  High gain PIN otherwise

6. Mean  2 per LED PB1 High near High far Low near Low far NOTE DIFFERENT VERTICAL SCALES

7. Mean  2 per LED PB2  <50% of LEDs OK  The ones that aren’t seem pretty random  I can supply the other PBs  Maybe somebody who knows the hardware can see a pattern?  LED 2 is missing High near High far Low near Low far

8. Mean  2 per LED (low values) PB1PB2 High gain Low gain near far near far

9. Conclusions and To Do  ?  I will do far v near pmt.  Far PMT  2 always better than near PMT.  Could be OK for linearising the near PMT if we assume the far PMT is linear. At least to the level required.  Not how it was designed to work.