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 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 different for the bars, its a little higher for the ARAPUCAs.


550 600 650 700 750 800 Mean Charge of 1st PE Peak 1 2 3 4 5 6 Number of Channels

ARAPUCA 1st Peak Means

ARAPUCA_BULK Entries 24 Mean 691.6 Std Dev 56.32

ARAPUCA 1st Peak Means

950 1000 1050 1100 1150 1200 1250 1300 Mean Charge of 1st PE Peak 2 4 6 8 10 12 14 16 18 20 22 Number of Channels

MPPC+Bars 1st Peak Means

MPPC_BULK Entries 60 Mean 1042 Std Dev 52.37

MPPC+Bars 1st Peak Means

950 1000 1050 1100 1150 1200 1250 1300 Mean Charge of 1st PE Peak 1 2 3 4 5 6 7 8 9 Number of Channels

MPPC+Dip-Coated 1st Peak Means

MPPC_DC Entries 33 Mean 1049 Std Dev 51.39

MPPC+Dip-Coated 1st Peak Means

950 1000 1050 1100 1150 1200 1250 1300 Mean Charge of 1st PE Peak 2 4 6 8 10 12 Number of Channels

MPPC+Double-Shift 1st Peak Means

MPPC_DS Entries 28 Mean 1038 Std Dev 57.3

MPPC+Double-Shift 1st Peak Means

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 affected 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 different. 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 affected by the MPPCs number connected in parallel, but in our calibrations we found in average a difference between them: SPE in ARAPUCAs ~ 0.7 SPE in bars MPPCs bars config MPPCs ARAPUCAs 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 affect 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 affected 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


20 40 60 80 100 120 140 160 180 200 Amplitude 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Charge 2 4 6 8 10 12 14 16 18 20 22

Charge vs. Amplitude, MPPC(TSV)+Dip-Coated, Ch. 243

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Charge 20 40 60 80 100 120 140 160 180 200 Events

Charge vs. Amplitude, MPPC(TSV)+Dip-Coated, Ch. 243

20 40 60 80 100 120 140 160 180 200 Amplitude 200 400 600 800 1000 Events

Charge vs. Amplitude, MPPC(TSV)+Dip-Coated, Ch. 243

Some consideration about after pulses can be made looking at the scatter plot “Charge vs Max Amplitude” As we can see the scatter plot shows a good linearity but it is not symmetric, events with after pulses populate the side in which events have more charge for fixed amplitude

Channel 264


20 40 60 80 100 120 140 160 180 200 Amplitude 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Charge 5 10 15 20 25 Events

Charge vs. Amplitude, ARAPUCA, Ch. 264

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Charge 20 40 60 80 100 120 140 160 180 Events

Charge vs. Amplitude, ARAPUCA, Ch. 264

20 40 60 80 100 120 140 160 180 200 Amplitude 200 400 600 800 1000 Events

Charge vs. Amplitude, ARAPUCA, Ch. 264

The same plot for ARAPUCAs shows a behavior more symmetric, indication of less after pulses

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 effects affecting 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. 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

μs

Events from background are uniformly distributed and their effect 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 effect 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. The Poisson distribution is a powerful tool since from the number of zero events and the total events can be entirely determined:

• >

is the average events per waveform window, it can be write as 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

P(n) = λne−λ n! P(0) = λ0e−λ 0! = e−λ λ = − ln ( N(0) NTOT) λ λ = T ⋅ R μs

In both our case (Ch_243 and Ch_264) we have 10k events. For Ch_243 N(0)=6818 empty waveforms of 10000 ticks.

• evt/window -> Event rate: R~57.4 kHz

For Ch_264 N(0)=9121 empty waveforms of 10000 ticks.

• evt/window -> Event rate: R~13.8 kHz

From the integrated charge we can get the charge per background event

Ch_243: 664.7 / 0.38 = 1749 (ADU*tick) Ch_264: 207.4 / 0.092 = 2254 (ADU*tick)


λ = − ln ( N(0) NTOT ) = 0.38 λ = − ln ( N(0) NTOT ) = 0.092 Qevt = Qtot λ

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 ARAPUCA config MPPCs bar 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 photons detected per each pulse. In the two case we measure: Ch_243: N(0)=912 Ch_264: N(0)=327

• λ

NTOT = 10k

Using the information from the background rate we can correct the numbers

• f zeros considering that part of them are affected by background events.
• Now

=500 ticks =300 ticks

Ch_243: Ch_243: N_c(0)=912(1+0.114) = 1016 Ch_264: Ch_264: N_c(0)=327(1+0.046) = 342

• Ch_243:

Ch_264: The average charge per event corrected by the background contribute is: Ch_243: <Q>_c= 3806- 199=3607 Ch_264: <Q>_c= 3105- 104=3001

N(0)C = N(0) + N(0)B = N(0) + N(0) ⋅ λB Tch264 Tch243

λB = 0.38 → λB = 0.114 λB = 0.092 → λB = 0.046 λ = − ln ( NC(0) NTOT ) λ = 2.3 γ/evt λ = 3.6 γ/evt < Q > /γ = 1568 ADU ⋅ ticks < Q > /γ = 833 ADU ⋅ ticks

Comparing these results with the previous calibration we can extrapolate the average number of avalanches per photon detected:

Ch_243: Ch_264: Ch_243: 1SPE= 924 (ADU*tick) Ch_264: 1SPE= 758 (ADU*tick) Ch_243: 1.69 avalanches Ch_264: 1.10 avalanches

< Q > /γ = 1568 ADU ⋅ ticks < Q > /γ = 833 ADU ⋅ ticks 1γ = 1γ =

Here is reported old values estimated with a very rude analysis, for the ARAPUCA channels.

Ch.

• 132 1252.38 1.6013

133 1236.63 1.64949 134 1249.04 1.60092 135 1280.46 1.63491 136 1296.59 1.5962 137 938.33 1.41081 138 1054.37 1.43198 139 892.565 1.41565 140 946.693 1.4073 141 932.123 1.48522 142 1314.39 - 143 1602.02 - 264 999 1.31777 265 1068.47 1.37018 266 1069.78 1.38519 267 895.881 1.42702 268 1225.38 1.5241 269 788.723 1.23916 270 860.634 1.2876 271 1074.08 1.45598 272 918.571 1.43886 273 1230.66 1.6311 274 1274.27 - 275 1110.41 1.3359

< Q > /γ

SPE/γ

…Work in progress In the next days we will do a similar analysis for all the channels. Please let us know if there are some suggestion or comment about it.

For these values the background corrections were not take into account so the number are a little bigger.

Backup slides on scatter plot “Charge vs Amplitude” ch 264

Scatter plot “Max Amplitude vs Charge” made with waveforms filtered. The charge is not affected by the filter The max amplitude results a bit reduced by the filter