January 26^{th}, 2022

Recently we received a new *MCP-PMT of type PP2365AC* manufactured by Photonis

The *triple beta scan method* allows to determine the time resolution of three devices without knowing any of them beforehand. The method consists on performing three different beta scans combining each pair of detectors. Each of these three beta scans is an "ordinary beta scan" as the one described in

The three devices used for this experiment were:

- LGAD "Speedy Gonzalez 11", AIDA-2020 V1 RUN 11478 W5-DA11.
- Mounted in Chubut board.
- No second stage amplifier.

- LGAD "Speedy Gonzalez 12", AIDA-2020 V1 RUN 11478 W5-DA12.
- Mounted in Chubut board.
- No second stage amplifier.

- Photonis MCP-PMT PP2365AC.
- Connected straight to the 50 Ω input of the oscilloscope without any amplification at all.

The window of the MCP-PMT was covered with thin aluminum adhesive tape to prevent ambient photons to enter into the device. This proved to be enough shielding to allow the device to be used under ambient light conditions without issues

In

Each of the three beta scans collected a total of 3333 events in coincidence of the two respective detectors. Each signal was then individually processed to extract its features using the lgadtools package for Python

The values of the "time at $x$ %" extracted from the analysis shown in

The final values reported (later on) for each $\sigma_\text{measurement}$ were obtained as $$ \sigma = 1.4826 \times \text{MAD} $$ where $\text{MAD}$ is the median absolute deviation. This estimator is practically equivalent to the standard deviation but more robust against outliers

The results obtained from 5 beta scans are summarized in

Device A | Device B | Measured σ (ps) | |
---|---|---|---|

Beta scan 1 | Speedy Gonzalez 11 | Speedy Gonzalez 12 | 53.1±1 |

Beta scan 2 | Speedy Gonzalez 11 | Photonis @ 2650 V | 45.2±0.9 |

Beta scan 3 | Speedy Gonzalez 12 | Photonis @ 2650 V | 44.5±0.8 |

Beta scan 4 | Speedy Gonzalez 11 | Photonis @ 3000 V | 45.2±0.9 |

Beta scan 5 | Speedy Gonzalez 12 | Photonis @ 3000 V | 42.2±0.8 |

- 20220124162416_BetaScan_SpeedyGonzalez_CH3DA11_CH4DA12
- 20220125124008_BetaScan_CH1Photonis_CH3SpeedyGonzalez11
- 20220125132535_BetaScan_CH1Photonis_CH4SpeedyGonzalez12
- 20220125145433_BetaScan_CH1Photonis3000V_CH4SpeedyGonzalez
- 20220125161743_BetaScan_CH1Photonis3000V_CH3SpeedyGonzalez11

Using this data and

- Using beta scans 1, 2 and 3: characterize the MCP-PMT at 2650 V, which is the nominal voltage.
- Using beta scans 1, 4 and 5: characterize the MCP-PMT at 3000 V, which is the maximum voltage.

Beta scans used | Speedy Gonzalez 11 (ps) | Speedy Gonzalez 12 (ps) | Pohtonis MCP-PMT (ps) |
---|---|---|---|

1,2 and 3 | 38.0±1.0 | 37.1±1.1 | 24.5±1.6 |

1, 4 and 5 | 39.3±1.0 | 35.8±1.1 | 22.4±1.7 |

We see that the time resolution for both of the Speedy Gonzalez devices is on the order of 38 ps. Using the measured σ from the beta scan 1 alone and assuming that the two devices are identical (which should be the case) a value of $\frac{53.1\text{ ps}}{\sqrt{2}}\approx 37.5\text{ ps}$ which is consistent. For the MCP-PMT the time resolution is on the order of 22-24 ps at the two different voltages. There seems to be a slight improvement with increasing the bias voltage but it is not important.

The time resolution of two LGADs and our new MCP-PMT was determined by means of the "three beta scans method". For the two LGADs a time resolution of 37 ps was obtained while for the MCP-PMT a value of 22-24 ps was determined. These values are not in perfect agreement with the expected ones. For the two Speedy Gonzalez LGADs a value of 27 ps was determined in the past