Hybrid Avalanche Photo-Detector Research Articles

Operation and performance of the Belle II Aerogel RICH detector

The Belle II experiment at the SuperKEKB asymmetric-energy e+e− collider is a B factory experiment to search for new phenomena beyond the Standard Model. One of the most important keys in the experiment is particle identification, in particular the separation between kaons and pions. Therefore, a proximity focusing Aerogel Ring Imaging Cherenkov (ARICH) counter is used in the forward endcap region to distinguish kaons and pions with momenta up to 4 GeV/c. The ARICH counter consists of a silica aerogel radiator and Hybrid Avalanche Photo Detectors (HAPDs). When a charged particle passes through the radiator, Cherenkov photons are emitted and then detected by the HAPDs.The Belle II experiment started its physics run in 2019 and collected 424 fb−1 of collision data. The ARICH counter is running stably and the performance is in line with our expectations. We report the details of the operation of the HAPDs and the readout electronics. We also report on the performance of the ARICH counter based on the data.

Operation and Performance of Belle II Aerogel RICH Counter

The Belle II experiment at the SuperKEKB aims at collecting 50 times more data than its predecessor Belle. One of the key components in the experiment is the particle identification (PID), especially the separation of kaons and pions. In the Belle II spectrometer, a proximity focusing ring imaging Cherenkov detector using aerogel as a radiator (ARICH) is equipped for the PID at the forward endcap. In this counter, a total of 420 of hybrid avalanche photo-detectors (HAPDs) with 144 channels are used as position-sensitive photon detectors that work inside a 1.5 T magnetic field. Belle II started the physics run with full detectors from 2019. We report on the operation of ARICH, including the fraction of dead channels, stability of HAPDs, and encountered problems. We also report the PID performance of ARICH estimated with using , D 0 → K − π + control sample with the initial data.

Performance of the Belle II aerogel-based ring-imaging Cherenkov counter system in SuperKEKB 2019 phase 3 operation

In the Belle II experiment, an aerogel-based proximity focusing ring-imaging Cherenkov (ARICH) counter is used for charged particle identification (PID) in the forward end-cap region. The goal is to separate kaons from pions at above 4σ significance level for momenta up to 4 GeV/c, which is critical for the measurements of rare B decays and CP violation in B decays. Chrerenkov photons are emitted in aerogel tiles and 144-channel Hybrid Avalanche Photo Detector (HAPDs) are used as the photo-detectors. We utilize a two-layer aerogel design with different refractive indexes in a focusing configuration. In Phase 3 of the Belle II operation (from Apr. 2019), the ARICH system has been operating smoothly. The performance of particle identification with ARICH has been well validated and is in agreement with simulation.

Performance and commissioning of HAPDs in the Aerogel RICH counter

The Belle II Aerogel Ring Imaging Cherenkov (ARICH) counter uses the angular distribution of Cherenkov photons emitted in silica aerogel to discriminate between charged pions and kaons. The Hybrid Avalanche Photo Detector (HAPD) is used as the photo-sensor, and is clearly the most critical component of the detector. HAPDs were installed into ARICH in July 2017, and ARICH was installed in the Belle II spectrometer in the end of 2017. During the Belle II beam commissioning in spring 2018, the performance of HAPDs was evaluated through measurements of the offset value, noise level and pulse height. Long term stability of the signal-to-noise ratio and the fraction of dead channel was also monitored. The signal-to-noise ratio exceeded 6, and the fraction of dead channels was less than 1%. The results of the performance evaluation and of the commissioning showed that the ARICH counter fulfills the requirements.

Particle identification in the Belle II experiment

The Belle II experiment integrates two dedicated particle identification (PID) subdetectors for pion/kaon separation. The Aerogel Ring Image Cherenkov (ARICH) detector is a forward region PID detector based on two layers of aerogel read out by hybrid avalanche photo detectors. The Time of Propagation (TOP) detector is a novel Cherenkov barrel PID system built for the Belle II detector upgrade based on quartz radiator bars read out by Micro-Channel Plate PMTs. The readout electronics of the TOP system are built around a switched capacitor array waveform sampling ASIC operating at 2.7 GSa/s. Acquired waveforms are processed in real time in the front-end electronics, extracting the individual timing of detected photons to better than 100 ps. This contribution presents the concept of the Belle II particle identification systems with a focus on the current status of commissioning, calibration and operation of the Belle II TOP detector.

Front-end electronics of the Belle II aerogel ring imaging detector

A proximity focusing RICH detector with an aerogel radiator is used for charged particle identification in the forward end-cap of the Belle II spectrometer. The detector, consisting of a 4 cm aerogel radiator, a 16 cm expansion volume and a photon detector with 420 Hybrid Avalanche Photo Detectors, is mounted in a very confined space between Central Drift Chamber and Electromagnetic Calorimeter, allowing only 5 cm of space for the readout electronics. In our solution, low power front-end read-out boards are mounted at the back side of each of the HAPD photosensors. These boards have each been tested individually before their installation onto the photosensors and into the spectrometer. Most important design issues and first experiences with the aforementioned front-end read-out boards are presented in this contribution.

First experience with Belle II Aerogel RICH detector

Abstract The Aerogel Ring-Imaging Cherenkov (ARICH) detector provides particle identification information in the forward endcap part of Belle II. It efficiently separates charged kaons from pions for momenta between 0.5 GeV/c and 4.0 GeV/c. Optical photons are emitted in a double layer aerogel radiator and detected by Hybrid Avalanche Photo Detectors. ARICH was installed in Belle II at the end of 2017, the first phase of a complex detector calibration of electronic signals and preparation for physics signals calibration has been successfully concluded. Cherenkov rings, created by cosmic rays as well as by charged particles from beam collisions, have been observed. The kaon identification efficiency using D ± ∗ decays has been studied and its calibration is expected by the end of the commissioning phase when sufficient data is available.

Development of slow control system for the Belle II ARICH counter

A slow control system (SCS) for the Aerogel Ring Imaging Cherenkov (ARICH) counter in the Belle II experiment was newly developed and coded in the development frameworks of the Belle II DAQ software. The ARICH is based on 420 Hybrid Avalanche Photo-Detectors (HAPDs). Each HAPD has 144 pixels to be readout and requires 6 power supply (PS) channels, therefore a total number of 2520 PS channels and 60,480 pixels have to be configured and controlled. Graphical User Interfaces (GUIs) with detector oriented view and device oriented view, were also implemented to ease the detector operation. The ARICH SCS is in operation for detector construction and cosmic rays tests. The paper describes the detailed features of the SCS and preliminary results of operation of a reduced set of hardware which confirm the scalability to the full detector.

Development of the ARICH monitor system for the Belle II experiment

The Belle II detector is under construction at KEK in Japan. In the forward endcap region of the Belle II detector, particle identification (PID) is performed by the Aerogel Ring Imaging Cherenkov (ARICH) counter composed of aerogel tiles and 144-channel Hybrid Avalanche Photo-Detectors (HAPDs). The photon detection efficiency of the photosensor is important for a stable operation of the ARICH. To examine the performance of the HAPDs periodically, a monitor system using scattered photons injected by optical fibers is being developed. In this paper, we report the test using the prototype monitor system and the tests with a partially built ARICH detector.

Test of the HAPD light sensor for the Belle II Aerogel RICH

The Aerogel Ring-Imaging Cherenkov detector (ARICH) is being installed in the endcap region of Belle II spectrometer to identify particles from B meson decays by detecting the Cherenkov ring image from aerogel radiators. To detect single photons, high-sensitive photon detector which has wide effective area (∼70mm × 70mm), a Hybrid Avalanche Photo Detector (HAPD), has been developed in a collaboration with Hamamatsu K.K. The HAPD consists of hybrid structure of a vacuum tube and an avalanche photodiode (APD). It can be operated in 1.5T magnetic field of the spectrometer and withstands the radiation levels expected in the Belle II experiment. There are two steps of electric pulse amplification: acceleration of photo-electron in electric field in the vacuum tube part and electron avalanche in the APD part resulting in total gain of order 105. For the ARICH, we use 420 HAPDs in total. Before installing them, we performed quality assessment studies such as measurements of dark current, noise level, signal-to-noise ratio and two-dimensional scan with laser illumination. We also measured quantum efficiency of the photocathode. During the HAPD performance tests in the magnetic field, we observed very large signal pulses which cause long dead time of the readout electronics in some of the HAPDs. We have carried out a number of studies to understand this phenomenon, and have found a way to mitigate it and suppress the degradation of the ARICH performance. In this report, we will show a summary of the HAPD performance and quality assessment measurements including validation in the magnetic field for all of the HAPDs manufactured for the ARICH in the Belle II.

Studies of a hybrid avalanche photo-detector in magnetic field

For the Belle II spectrometer a proximity focusing RICH counter with an aerogel radiator (ARICH) will be employed as a PID system in the forward endcap region of the spectrometer. The main challenge was the development of a reliable multichannel sensor for single photons that operates in the high magnetic field of the spectrometer (1.5T) and withstands the radiation levels expected at the experiment. A 144-channel Hybrid Avalanche Photo-Detector (HAPD) was developed with Hamamatsu Photonics K.K. and the mass production of ∼480 HAPDs was completed recently. While our first tests of HAPD performance in the magnetic field (before mass production) showed no issues, we lately observed a presence of very large signal pulses (∼5000×single photon signal), generated internally within about 20% of HAPDs, while operating in the magnetic field. The rate of these pulses varies from sample to sample. These pulses impact the HAPD performance in two ways: they introduce periods of dead time and, in some cases, damage to the front-end electronics was observed. Here we present conditions under which such large pulses are generated, their properties and impact on HAPD performance, and discuss possible mechanism of their origin.

Particle identification performance of the prototype aerogel RICH counter for the Belle II experiment

We have developed a new type of particle identification device, called an Aerogel Ring Imaging Cherenkov (ARICH) counter, for the Belle II experiment. It uses silica aerogel tiles as Cherenkov radiators. For detection of Cherenkov photons, Hybrid Avalanche Photo-Detectors (HAPDs) are used. The designed HAPD has a high sensitivity to single photons under a strong magnetic field. We have confirmed that the HAPD provides high efficiency for single-photon detection even after exposure to neutron and gamma-ray radiation that exceeds the levels expected in the 10-year Belle II operation. In order to confirm the basic performance of the ARICH counter system, we carried out a beam test at the DESY using a prototype of the ARICH counter with six HAPD modules. The results are in agreement with our expectations and confirm the suitability of the ARICH counter for the Belle II experiment. Based on the in-beam performance of the device, we expect that the identification efficiency at 3.5 GeV/c is 97.4% and 4.9% for pions and kaons, respectively. This paper summarizes the development of the HAPD for the ARICH and the evaluation of the performance of the prototype ARICH counter built with the final design components.

Development of a 144-channel Hybrid Avalanche Photo-Detector for Belle II ring-imaging Cherenkov counter with an aerogel radiator

The Belle II detector, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron–positron collider at KEK in Japan. For the PID system in the forward region of the spectrometer, a proximity-focusing ring-imaging Cherenkov counter with an aerogel radiator is being developed. For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector has been developed with Hamamatsu Photonics K.K. In this report, we describe the specification of the Hybrid Avalanche Photo-Detector and the status of the mass production.

Aerogel RICH for the Belle II forward PID

The Belle II spectrometer, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron–positron collider at KEK in Japan. For the PID system in the forward region of the spectrometer, a proximity focusing ring-imaging Cherenkov (RICH) counter with an aerogel radiator is being developed. The counter will provide a 4σ separation of pions and kaons up to momenta of 4GeV/c. For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector (HAPD) has been developed with Hamamatsu Photonics K.K. The readout electronics is based on the custom developed ASIC. The design of the components is currently being finalized and part of their mass production have already started. Herein, we report the final design of the counter and a prototype test conducted with test beams at DESY.

Readout ASIC and electronics for the 144ch HAPD for Aerogel RICH at Belle II

At the Belle II experiment, Aerogel RICH is used as the particle identification device that covers the forward end-cap part of the Belle II detector. We develop the readout system of Hybrid Avalanche Photo Detectors that are used as the photon sensors of the Aerogel RICH. We present overview of the readout system, and report the status of the mass production toward the Belle II experiment.

Readout ASICs and Electronics for the 144-channel HAPDs for the Aerogel RICH at Belle II

Abstract The particle identification (PID) device in the endcap of the Belle detector will be upgraded to a ring imaging Cherenkov counter (RICH) using aerogel as a radiator at the Belle II experiment. We develop the electronics to read out the 70,000 channels of hit information from the 144-channel hybrid avalanche photodetectors (HAPD), of the aerogel RICH detector. A readout ASIC is developed to digitize the HAPD signals, and was used in a beam test with the prototype detector. The performance and plan of the ASIC is reported in this study. We have also designed the readout electronics for the aerogel RICH, which consist of front-end boards with the ASICs merger boards to collect data from the front-end boards. A front-end board that fits in the actual available space for the aerogel RICH electronics was produced.

Development of Ring Imaging Cherenkov counter for Belle II experiment at super KEKB

For the Belle II experiment at the superKEKB, we have been developing a proximity focusing ring imaging Cherenkov detector using a silica aerogel as a radiator. A 144-channel Hybrid Avalanche Photo-Detector which is developed with Hamamatsu Photonics K.K. was adopted as the photon detector for the Aerogel RICH counter. We have conducted beam tests in order to evaluate the particle identification performance for the A-RICH system. One of our current concern for the system is a radiation hardness of the HAPD. In order to realize the neutron hardness for 10-year Belle II operation, we have tried to make APDs with a thinner P-layer which is expected to help in reducing the leakage current. As a result, we actually confirmed effects of the improved APD. In this paper, we would alike to report the status of the A-RICH development, especially about the improvement of the HAPD.

Study of a 144 channel multi-anode hybrid avalanche photo-detector for the Belle II RICH counter

A new hybrid avalanche photo-detector has been developed as a photon sensor for the Belle II RICH counter. Single-photon response was investigated in the presence of a magnetic field and excellent performance was demonstrated. In addition, the radiation damage due to the neutron dose was studied. By building a prototype consisting of six photo-detectors, a test beam experiment was carried out. We successfully obtained a single-photon Cherenkov resolution of 13.5 mrad with 15.3 photoelectrons and achieved a π / K separation of more than 6 σ at 4 GeV/ c.

Study of 144-channel hybrid avalanche photo-detector for Belle II RICH counter

For the upgrade of the Belle detector at the KEKB collider, we are developing a proximity focusing ring imaging Cherenkov detector using a silica aerogel as a radiator. An array of 144 channel HAPD (Hybrid Avalanche Photo Detector) will be used as the photo-detector. We have measured performance of the HAPDs, and succeeded to read out single-photon signals from the HAPD using custom-made ASICs that have been developed for this purpose. We have also performed a beam test with a 2 GeV/ c electron beam and demonstrated more than 4 σ K / π separation performance at 4 GeV/ c.

Development of the readout ASIC for the 144ch HAPD for aerogel RICH

We have developed an ASIC for readout of a 144 channel HAPD (hybrid avalanche photo-detector), one of the candidate photo-detectors for use in the aerogel RICH detector of the Belle upgrade (Belle-II). The first series of ASICs for evaluation showed good performance, and have been used to successfully detect Cherenkov rings with a prototype aerogel RICH device. We are also developing a new version of the ASIC for real application at the Belle-II detector.