MPPCs calibration MPPCs response from bars configuration and - PowerPoint PPT Presentation

MPPCs calibration MPPCs response from bars configuration and ARAPUCAs configuration. Bryan Ramson Dante Totani Fermilab Fermilab University of L’Aquila Jan 15, 2019 


First peak mean distribution for MPPCs ARAPUCA 1st Peak Means ARAPUCA 1st Peak Means MPPC+Bars 1st Peak Means MPPC+Bars 1st Peak Means ARAPUCA_BULK MPPC_BULK 22 Number of Channels Number of Channels Entries 24 Entries 60 6 Mean 691.6 Mean 1042 20 Std Dev 56.32 Std Dev 52.37 18 5 16 4 14 12 3 10 8 2 6 4 1 2 0 0 550 600 650 700 750 800 950 1000 1050 1100 1150 1200 1250 1300 Mean Charge of 1st PE Peak Mean Charge of 1st PE Peak MPPC+Dip-Coated 1st Peak Means MPPC+Dip-Coated 1st Peak Means MPPC+Double-Shift 1st Peak Means MPPC+Double-Shift 1st Peak Means MPPC_DC MPPC_DS Number of Channels Number of Channels Entries 33 Entries 28 9 12 Mean 1049 Mean 1038 Std Dev 51.39 Std Dev 57.3 8 10 7 6 8 5 6 4 3 4 2 2 1 0 0 950 1000 1050 1100 1150 1200 1250 1300 950 1000 1050 1100 1150 1200 1250 1300 Mean Charge of 1st PE Peak Mean Charge of 1st PE Peak Upper left is ARAPUCA, upper right is MPPC+Bars, lower left is MPPC+Dip-Coated, lower right is MPPC+Double-Shift. The double shift and dip-coated sensors are on average within 1% of each other std dev of about 50 ADC di ff erent for the bars, its a little higher for the ARAPUCAs. 


Calibration using PE separation. The peak separation calibration, works fine for the SPE determination, but more considerations have to be done since a single gamma does not produce every time a single PE. First thing to observe is the structure of the 1 PE peak. As we can see there is a shoulder on the right of the peak. (it is in all peaks) The first higher symmetric peak is the one produced by pure SPE events. The shoulder is duo to events a ff ected by after pulses, which increase the charge. In the previous work we found that every time the 1st peak mean is bigger than the PE calibration. 


In these slides only one channel for the ARAPUCAs and one for the bars are take into account. Channel 243 was used for MPPC+Dip-Coated bar Channel 264 was used for MPPC in ARAPUCA The MPPCs configuration were di ff erent. Arapuca channels: 12 MPPCs connected in parallel Bar channels: 3 MPPCs connected in parallel For the two channels the calibration found in the PE separation analysis: Ch_243: 1SPE= 924 +/- 16 (ADU*tick). Ch_264: 1SPE= 758 +/- 4 (ADU*tick). 


SPE response MPPCs bars configuration MPPCs ARAPUCAs configuration ARAPUCAs configurations -> 12 MPPCs are connected in parallel. Bars configurations -> 3 MPPCs are connected in parallel.

When more MPPCs are connected in parallel the signal amplitude is smaller and the recovery time is longer. In principle the integrate charge should be not a ff ected by the MPPCs number connected in parallel, but in our calibrations we found in average a di ff erence between them: SPE in ARAPUCAs ~ 0.7 SPE in bars MPPCs ARAPUCAs config MPPCs bars config Integrate charge histograms for both configurations: the SPE peak is higher in the bars config.

First consideration on after pulses Observing the SPE peak structure, a shoulder appears on the right side of the peak. This is due to after pulses contamination. (It seems to a ff ect more the 3 MPPCs confine. than the 12 MPPCs config. ) For example using Ch. 243: Fitting a region around the symmetric higher peak and a the entire region of the first peak with a gaussian we found for the means: 922 +/- 4 (ADU*tick) and 1090 +/- 7 (ADU*tick).

From the calibration got from analyzing the peaks separation, Ch_243 has: 924+/- 16 (ADU*tick) per PE, number compatible with the fit of the symmetric region. This region represents pure SPE events. Sometime events are a ff ected by after pulses. So in average the SPE value have to be increased (~18% in this case) to take into account the after pulses. For Ch_264 the behavior is very similar but less evident. The two values found are: 728+/-6 (ADU*tick) and 762+/- 4 (ADU*tick) that means a 5% of charge due after pulses

Charge vs Max Amplitude Channel 243 
 Charge vs. Amplitude, MPPC(TSV)+Dip-Coated, Ch. 243 Charge vs. Amplitude, MPPC(TSV)+Dip-Coated, Ch. 243 10000 200 Charge Events 22 9000 180 20 8000 160 18 7000 16 140 14 6000 120 12 5000 100 10 4000 80 8 3000 60 6 2000 40 4 1000 20 2 0 0 0 0 20 40 60 80 100 120 140 160 180 200 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Amplitude Charge Charge vs. Amplitude, MPPC(TSV)+Dip-Coated, Ch. 243 Events 1000 Some consideration about after pulses can be made looking at the scatter plot “Charge vs Max 800 Amplitude” 600 400 As we can see the scatter plot shows a good 200 linearity but it is not symmetric, events with after 0 pulses populate the side in which events have 0 20 40 60 80 100 120 140 160 180 200 Amplitude more charge for fixed amplitude

Channel 264 
 Charge vs. Amplitude, ARAPUCA, Ch. 264 Charge vs. Amplitude, ARAPUCA, Ch. 264 10000 25 180 Charge Events Events 9000 160 8000 20 140 7000 120 6000 15 100 5000 80 4000 10 60 3000 40 2000 5 20 1000 0 0 0 0 20 40 60 80 100 120 140 160 180 200 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Amplitude Charge Charge vs. Amplitude, ARAPUCA, Ch. 264 Events 1000 800 The same plot for ARAPUCAs shows a 600 behavior more symmetric, indication of 400 less after pulses 200 0 0 20 40 60 80 100 120 140 160 180 200 Amplitude

Wider analysis on the calibration The final aim is to evaluate the charge associated to a single photon detected. As we have seen for the after pulses, a single detected photons does not produce every time only a single avalanche (the SPE charge). Besides the after pulses there are cross talks. They are more hard to detect since they produce the same avalanches of photons producing pure SPE. (1PE + 1 cross talk) = 2 PE A good calibration is got with a more complex procedure. Analyzing events where a LED was lighting the devices, the number of photons detected can be estimated through the Poisson distribution. The ratio between the charge measured for these events and the number of photons expected will give the charge produced per photon detected. This procedure takes into account all the extra e ff ects a ff ecting the SPE charge.

The events analyzed come from RUN 5927. The LED produced two near pulses and the SSPs were set to trigger on them in a fixed point. In the figure below is reported the average of 10000 waveforms for these events.

Background First of all, an evaluation of background events was made using a window of 1000 tick = 6.67 � in the first half waveform. μ s Ch_243: 664.7 (ADU*tick)/1000 tick of Background Ch_264: 207.4 (ADU*tick)/1000 tick of Background These background is not MMPCs dark counts but light that come from activity in Argon. At LAr temperature dark counts can be neglected. MPPCs ARAPUCA config MPPCs bar config

Events from background are uniformly distributed and their e ff ect is to add a bias to the average waveforms. In the plot above it is possible to see the bias introduced by the background. The e ff ect of this background is big as big as the window of integration. For the entire waveform, 2000 ticks, it introduces a contribute of the order of ~1 PE charge.

� Poisson distribution for background events Integrating a waveform (in an arbitrary window) give us information about the charge seen by the detectors but there are no informations about the number of events. The only sure information is when there are no events, the integral is zero. P ( n ) = λ n e − λ The Poisson distribution � is a powerful tool since from the number of n ! zero events and the total events can be entirely determined: λ = − ln ( N TOT ) P (0) = λ 0 e − λ N (0) = e − λ -> � 0! � is the average events per waveform window, it can be write as � λ λ = T ⋅ R where T is the window interval and R is the rate of events in that interval. 1000 ticks = 1000 x 6.67 ns =6.67 � μ s

� � In both our case (Ch_243 and Ch_264) we have 10k events. For Ch_243 N(0)=6818 empty waveforms of 10000 ticks. λ = − ln ( N TOT ) = 0.38 N (0) evt/window -> Event rate: R~57.4 kHz For Ch_264 N(0)=9121 empty waveforms of 10000 ticks. λ = − ln ( N TOT ) = 0.092 N (0) evt/window -> Event rate: R~13.8 kHz Q evt = Q tot From the integrated charge we can get the charge per background event � λ Ch_243: 664.7 / 0.38 = 1749 (ADU*tick) Ch_264: 207.4 / 0.092 = 2254 (ADU*tick) 


Calibration with LED Once got an idea of the background, analysis on the events was made looking at the peaks produced by LED. Integrating the signals in two window of 500 ticks for the 12 MPPCs config. and 300 ticks for the 3 MPPCs config. Ch_243: [1050:1350] and [1550:1850] Ch_264: [1000:1500] and [1500:2000] MPPCs bar config MPPCs ARAPUCA config

� Integrating the first window we got the following histograms: The number of photons produced by the LED at each pulse follow the Poisson statistic. ( Before we used the Poisson distribution to estimate the number of events in a given interval .) As before counting the zeros we can estimate the � parameter and from it the mean number of λ photons detected per each pulse. In the two case we measure: Ch_243: N(0)=912 Ch_264: N(0)=327 N TOT = 10 k