1. MPPC Measurements at LSU Brandon Hartfiel LSU Hardware Group Thomas Kutter, Jessica Brinson, Jason Goon, Jinmeng Liu, Jaroslaw Nowak Sam Reid January 2009 Collaboration Meeting

2. TFB Darkrate  We measure darkrate using the TFB. We integrate randomly triggered 250ns gates, fit the pedestal and 1pe to determine the.5 pe level and then count the number of events below.5 pe. We then calculate the darkrate by pedestal fraction= exp(-darkrate * gate width)  This calculation assumes that the pulses are randomly distributed in time. Afterpulses are not. Assuming the time distribution of afterpulses is distributed as an exponential, we can calculate the expected difference between our darkrate method and the threshold crossing rate ALTERNATE METHOD We also measure the darkrate using the fit values of the pedestal and 1 pe (with 2pe background) instead of using a cut at.5 pe

3. TFB Darkrate Comparing 20C to 25C Relative change per degree C 4.2 +/-.4 % per degree bias voltage - nominal darkrate (kHz) cut method fit method at 25 C and nominal bias Hamamatsu rate our TFB rate slope =.86 purple limits match our rate / threshold crossing rate afterpulse creation probability tau Simple Simulation at 700kHz Thermal rate. No deadtime. No recharge Time 8.9% per 100mV all profile plots have RMS errorbars Temperature changes are defined as

4. Scalar Darkrate A threshold crossing rate is taken for 40 sensors at.5pe with 26ns deadtime (determined by the width of our preamp output) Hamamatsu rate Our Scalar Rate Now the slope is.94 The ratio of slopes for the 2 LSU measurements is.915 LSU TFB rate/ LSU scalar rate tau afterpulse creation probability LSU data ratio in purple black lines are the results from page 12

5. Gain The TFB gain is calibrated using the internal calibration system with the sensors biased at 60V. We appear to have made a mistake as our gains are consistently 25% high. Gain is measured between the pedestal and 1pe in LED runs with and average of 2.5 pe per event ALTERNATE METHOD We also measure the gain from dark spectra

6. Gain Comparing 20C to 25C Relative change per degree C -3.7 +/-.2 % per degree bias voltage - nominal gain LED run Dark run at 25C and nominal bias gain 7.7% per 100mV sigma 2.9%

7. Crosstalk + Afterpulses  Random trigger dark ADC spectra – Pedestal, 1pe and 2pe are fit with Gaussians. Pedestal fraction is used to predict the 1pe fraction. A deficit implies an excess of > 1pe events which could be either afterpulses or crosstalk  ALTERNATE METHOD The LED run ADC spectra are fit using a poisson function modified to include a probability that each original pulse create one crosstalk or afterpulse.

8. Crosstalk + Afterpulses Comparing 20C to 25C Relative change per degree C -6.9 +/-.5 % relative per degree bias voltage - nominal CT + AP creation probability dark runs LED runs 25 C and nominal bias probability of creating a new pulse 14.9% relative per 100 mV sigma 6.5% relative

9. Relative PDE Three reference sensors are included with every run and always kept at their nominal bias voltage The LED ADC spectra are fit using the poisson + AP+ CT function. The average number of pe is divided by the average for the 3 reference sensors.

10. Relative PDE Comparing 20C to 25C Relative change per degree C -1.3 +/-.4 % per degree at 25C and nominal bias pe / pe of reference sensors relative pde bias-nominal 6.0% per 100mV sigma 3.3%

11. Afterpulses Only (example TA8088 25C).5 pe threshold crossing rate is measured with different deadtimes after the pulses. This is compared to the expected rate if the pulses were not correlated in time. red – fit to expectation if pulses are random in time seen rate=real rate/(1+deadtime*real rate) black - data deadtime (ns) rate kHz derivative of the difference kHz/ns time since original pulse (ns) afterpulse rate 138kHz tau = 80 ns

12. Afterpulses Only sensor number ap creation probability tau COMPARE WITH PAGE 4 sensor number The “afterpulse probability” is the integral of the fit on the right of the previous page, starting at 0 ns, divided by the intersection of the red line with the y-axis on the left plot. It does not consider the possibility of afterpulses of afterpulses and so is an overestimation of the actual probability.

13. afterpulse vs temperature sensor number relative change per degree

14. Afterpulses vs Bias Voltage for 3 MPPCs 4.5% absolute per 100mV afterpulse probability Bias-Nominal Tau Bias-Nominal

15. Conversion factors LSU/INR Sensorgain x10^6 DarkratePDE compared to our reference TA9307.0376.883.0826 TA9309.0390.865.0882 TA9310.0375.865.0846 TA9314.0408.936.0847 Average.0387.887.0851 % standard deviation 4.0%3.8%2.7% note: these correction are large because different units were used e.g. number of electrons vs number of ADC bins

16. EXTRA SLIDES

17. Our Reference Sensors 21.5C and Hamamatsu nominal bias Sensorgain x10^6 Darkrate kHz PDE compared to our reference CT+AP creation probability % TA78811.1816301.0525.3 TA78931.1704921.0630.0 TA79301.1106451.0626.4 TA79761.1776271.0527.6 TA80971.088606.9656.0 ? TA81201.1255041.0223.5 TA81601.1575101.0123.8

18. Sensors we received from INR 25C and Hamamatsu nominal bias Sensorgain x10^6 Darkrate kHz PDE compared to our reference CT+AP creation probability % TA9307.9589311.0018.4 TA9309.9909091.0519.1 TA9310.970877.9920.0 TA93141.0078201.0020.1

19. 1.5 pe and 2.5 pe scalar rates Sensor1.5 pe rate kHz 2.5 pe rate kHz TA930712614 TA930912414 TA931011914 TA931411714 TA8097819 TA8120647 TA8160718

20. results vs position dark/hamamatsu darkgain CT+AP relative pde

21. TA8097 vs day between dec 13 and dec 20 a bad channel was dropping all voltages by.08 this has been corrected for on all other plots

22. TA8160 vs day between dec 13 and dec 20 a bad channel was dropping all voltages by.08 this has been corrected for on all other plots

23. TA8120 vs day between dec 13 and dec 20 a bad channel was dropping all voltages by.08 this has been corrected for on all other plots

24. Bad Sensors Sensor TE5020 was dropped into an unaccessible place 11 sensors failed to meet our cuts at least twice. Some fraction of these failures are probably due to human error, but we decided to put these aside just to be safe one had the wrong bias voltage two had very bad fits two have PDE ~35% too high 6 were only 15% different from normal