Tests with JT0623 & JT0947 at Indiana University Nagoya PMT database test results for JT0623 at 3220V: This tube has somewhat higher than usual gain. 5×10 5 is far from the measured points. Therefore I first try to look at the lowest voltage measurement point. G. Visser 4/24/2015 (latest update) I looked at channel 2 and channel 3, according to Hamamatsu numbering Channel 2 Channel 3

This is the same dataset analyzed on following pages. 2,200,000 events. note there is sometimes ADC saturation

Scope data exported as integer (ADC units), and then summed as integer.  No binning artifacts (except for real DNL of course).

crosstalk events P.O.U.W. (pulses of unusual width), mostly two-photon events ADC saturation crosstalk events (bipolar shape)

18326 events (0.83%) removed by these cuts (three lines + no ADC saturation)

Blue: with cut as above This fall is due to scope dynamic range limitation, of course. Not real.

Pedestal fit f(x)=a*exp(-(x-x0)**2/(2*σ**2)) a= / x0= / σ= /  events in pedestal  signal / = 4.5%

Rescale x with pedestal mean and theoretical scale charge/icharge = Melectrons (from assumed load resistance, scope V/div and sample rate). Fit whole curve (from 0.11 to 3.1 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + pedestal fit from before (as a fixed background). Really should consider electronics noise in signal, fixing same sigma as pedestal, this is oversimplified here. Signal in fit g(x)=b*x**p*exp(-x**q/c) b= / p= / q= / c= /  events in signal ( to 3.2 Melectrons) (expected = the lost tail) – good agreement  mean signal size Melectrons JT0623/ch V Pedestal σ = Melectrons

Same plot except on linear scale mean of all (as above) mean for >0.13 mean for >0.25 threshold (e.g. of discriminator if used) can make a 10% difference JT0623/ch V

Repeated all the above on another, independent data run 2.2Mevents, same HVB voltage. Result: Mean charge 1.04 Melectrons. Probably this is representative of +/-5% or so statistical error in the method. Some of this might be due to sensitivity to “arbitrary judgement” tuning fit limits. Next, we look at the nominal 5x10 5 gain voltage for this channel. From database, the gain fit equation is G=exp( *V-15.59) and so we need to set to 3046 V. Note that is a ~180 V extrapolation from the measured datapoints (which span 200 V). I don’t know what accuracy is expected… Mistake was made – that was ch3 nominal 5x10 5 gain voltage. Oops. My results from 3046 V are on following three pages. I don’t show all the initial analysis details just the end results, but method of analysis was similar. Scope is now set to 2 mV/div.

JT0623/ch V ignore the wiggles – a little crosstalk from LED drive

Charge histogram method as before. Fit pedestal first, then fit whole curve (from 0.08 to 1.22 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit. Signal in fit g(x)=b*x**p*exp(-x**q/c) b= / p= / q= / c= /  events in signal ( to 1.27 Melectrons) [We expected (cut) (pedestal fit) = events in signal. Good.]  mean signal size Melectrons JT0623/ch V Pedestal σ = Melectrons

Same plot except on linear scale JT0623/ch V

JT0623/ch V Pedestal σ = Melectrons Charge histogram method as before. Fit pedestal first, then fit whole curve (from 0.10 to 3.00 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit. Signal in fit g(x)=b*x**p*exp(-x**q/c) b = / p = / q = / c = /  events in signal ( 4.2% ) [We expected −19542(cut) − (pedestal fit) = events in signal. Good.]  mean signal size Melectrons

Same plot except on linear scale JT0623/ch V

Summary / comparison with Nagoya PMT database test results (Nagoya channel number = Hamamatsu channel number − 1) NagoyaIUratio Nagoya/IU 3220 V1.61 Me0.972 Me V0.831 Me (projected)0.353 Me V0.500 Me (projected)tbd 3220 V1.15 Me0.758 Me V0.500 Me (projected) ch3 / 3220 V This seems to indicate a discrepancy in measured points, by about a factor 1.5 It’s necessary to try to confirm calibration of IU method by an independent method, see following slides – results seem confirmed It seems there is a further discrepancy in projecting from measured points down to 0.5 Me gain level. In my opinion the gain fit function G=G 0 e αV does not have enough freedom to match the real data.

We may suspect some large >>5% error in the calibration here if: The load resistance, or scope voltage or time scale is out of calibration? (Not likely!) Summing the scope ADC samples doesn’t give a good estimate for charge integral? (i.e. Nyquist vs. Riemann) There is charge lost elsewhere? (Stray capacitances remove something from pulse and only comes back slowly? Not likely but…) Integration gate not correct? (But clearly it’s ok in scope photo!) Fit is not good and so mean of fit doesn’t estimate mean of signal data? (But it looks reasonable I think we all agree…) Bug in scope, or in analysis? To check this, I set up the LED pulser to a much higher rate (500 kHz rather than 500 Hz used above). Then directly measured the anode current on a picoammeter, and used the scope method to estimate only the fraction of signal events but not the mean amplitude. To make a better comparison, I do not cut the multi-photon events from the data. The LED amplitude and PMT gain may be shifting between 500 Hz and 500 kHz. Also the LED is not in precisely same location as before (I had to remove bleeder resistor from the setup, disturbing it). Therefore what we want to compare is the gain determined from picoammeter current and scope-method signal fraction, to the gain determined by scope method on the same 500 kHz data set. Results on following slides…

JT0623/ch V 500kHz 2-photon not cut Pedestal σ = Melectrons Charge histogram method as before. Fit pedestal first, then fit whole curve (from to 3.00 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit. Signal in fit g(x)=b*x**p*exp(-x**q/c) b = / p = / q = / c = /  events in signal ( 6.98% ) [We expected −22972(cut) − (pedestal fit) = events in signal. Moderate agreement, (20%), maybe due to distorted pedestal from baseline wander at the high rate.]  mean signal size Melectrons Current method (using Keithley #2485): LED on: −4.793 nA LED off: nA (just background/offset of the meter) Calculated mean signal: nA/(500 kHz * 6.98%) = Melectrons This is pretty good agreement (0.862/0.807) with the integrate/fit method, I think. Some extra current is to be expected from afterpulsing, which is outside the integration gate.

Same plot except on linear scale JT0623/ch V 500kHz 2-photon not cut

Move on to JT0947 Nagoya PMT database test results for JT0623 at 3010V: I looked at channel 2 and channel 3, according to Hamamatsu numbering Channel 2 Channel 3 This is from the newer procedure, where measured data comes closer to 5e5 gain, no large extrapolation is involved.

JT0947/ch V Pedestal σ = Melectrons Charge histogram method as before. Fit pedestal first, then fit whole curve (from to 0.70 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit. Signal in fit g(x)=b*x**p*exp(-x**q/c) b = / p = / q = / c = /  events in signal ( 6.3% ) [We expected −12612(cut) − (pedestal fit) = events in signal. Good.]  mean signal size Melectrons

Same plot except on linear scale JT0947/ch V

JT0947/ch V Pedestal σ = Melectrons Charge histogram method as before. Fit pedestal first, then fit whole curve (from 0.11 to 2.36 Melectrons) to a phenomenological form (red curve) for signal ignoring electronics noise + the fixed pedestal fit. Signal in fit g(x)=b*x**p*exp(-x**q/c) b = / p = / q = / c = /  events in signal ( 6.3% ) [We expected −22086(cut) − (pedestal fit) = events in signal. Good.]  mean signal size Melectrons

Same plot except on linear scale JT0947/ch V

Summary / comparison with Nagoya PMT database test results (Nagoya channel number = Hamamatsu channel number − 1) NagoyaIUratio Nagoya/IU JT V 1.61 Me0.972 Me1.67 JT V Me (projected)0.353 Me2.35 JT V 1.15 Me0.758 Me1.52 JT0623 ch3 / 3220 V JT V 0.63 Me0.197 Me3.20 JT V 1.72 Me0.664 Me2.59