LI Gain Curves Peter Litchfield Calibration Workshop, 6 th September 2005  Beginning to understand the LI system  Beginning to understand the software system  Not there yet, not guaranteed error free  Probably many of my conclusions are already well known 1)Known corrections  Zeros  Electronics saturation (Giles) 2)A first look at some random LED/strip combinations

What do we have?  Due to the foresight of the system designers we have some redundancy.  Each time light is injected at one end of a strip we read out  A low gain PIN and the near end PMT  A high gain PIN and the near end PMT  A low gain PIN and the far end PMT  A high gain PIN and the far end PMT  Each PIN has two PMTs associated with it and each PMT two PINS, we can compare for consistency.  At the far end the light is attenuated so we largely avoid saturation effects

Zero Correction PIN ADC PMT ADC Uncorrected Corrected  At low light levels some pulses drop below threshold  The PMT pulses are spread by photon statistics, need to correct for zero readouts.  The PINs have much more light, spread is narrow but the mean can be below the sparsification threshold  All the fits I shall show have no constant term, i.e. pass through (0,0). I see no evidence that a constant term is needed.

Saturation correction  Giles has produced a correction for the electronics saturation based on charge injection  His brief so far has been to do it just for pins, pmt saturation should be correctable from the gain curve. However, on the assumption that the electronics saturation is the same for everything he has set up a single overall correction for all channels.  The correction is only significant above ADCs of ~8000. But it does funny things above ACDs of ~12000  Sorry about the vertical scale, ROOT’s fault

PB3 LED1 Pl 67 St 174 Far PMT  Both high and low gain PIN versus PMT ADC plots are linear  Zero correction at low PMT pulse heights. Lowest low gain PIN had no hits  Looked at 20 strips in this configuration. Essentially all plots show the same features. Maybe some evidence for a deviation below the straight line at highest PMT ADCs High gain PIN Low gain PIN PMT ADC PIN ADC Residual PIN ADC

PB3 LED1 Pl 67 St 174 Near PMT  Same LED and PIN, Near PMT  Same structure in low and high gain PIN  Giles correction not sufficient at high ADC  Up to 3000 PMT ADC (range at far side), quite linear)  PMT non-linearity, ~5% over the range ADC

PB2 LED3 Pl 65 St 165 Far PMT  PMT v low gain PIN is linear  PMT v high gain PIN is non-linear  Same PMT  High gain PIN is non- linear

PB2 LED3 Pl 65 St 165 Near PMT  Different PMT, same PIN  Same behaviour  High gain PIN is non- linear

PB2 LED15 Pl 65 St 50 Far PMT  High Gain PIN-far PMT is linear  Low Gain PIN-far PMT is non-linear  Low Gain PIN is non linear  High Gain PIN is linear

PB2 LED15 Pl 65 St 50 Near PMT  Near PMT same LED and PINS  High Gain PIN –Near PMT quite linear  Low Gain PIN – Near PMT non-linear  Same structure as for far PMT  Low Gain PIN non- linear

Conclusions  The gain curves are non-linear  Non-linearity varies with LED and PIN, sometimes small, sometimes up to ~5-10%  Known corrections, zeros and electronics saturation, do not correct the non- linearities  The PMTs may show normal saturation effects  The PINs are non-linear, sometimes in the high gain and sometimes in the low gain, probably sometimes both  What causes it?  Crosstalk?  ?  What do we do about it?  ?