Calibration of the Belle II aerogel ring imaging detector

International audienceFor efficient separation of hadrons in the forward end-cap of the Belle II spectrometer, an aerogel proximity focusing Ring Imaging Detector is installed in the high magnetic field between the central drift chamber and electromagnetic calorimeter. Cherenkov photons, emitted in the double layer aerogel radiator are expanded through the empty space and detected on the photon detector consisting of Hybrid Avalanche Photo diodes. The readout electronics working in a threshold mode records hit patterns registered during beam collisions. A particle identification algorithm based on the two dimensional extended maximum likelihood technique is used to assign probabilities for different particle hypotheses of tracks traversing the aerogel RICH detector. For efficient discrimination, the Aerogel RICH detector has to be calibrated. We present the key calibration steps used to optimize the detector performance

Development of alignment algorithm for Belle II Aerogel RICH counter

International audienceWe have developed an alignment algorithm for the Belle II Aerogel RICH (ARICH) counter using the Monte Carlo simulation of e+e−→μ+μ− . We applied the developed algorithm to the e+e−→e+e− data obtained at the commissioning of Belle II, and found the displacement and rotation of ARICH to be around 1mm and less than 0.01 ∘ , respectively, which is consistent with the values estimated from mechanical tolerance

First experience with Belle II Aerogel RICH detector

International audienceThe 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

Aerogel-Based Ring-Imaging Cherenkov counter in the Belle II experiment

International audienceIn the charged particle identification system of the Belle II experiment, an aerogel-based proximity focusing ring-imaging Cherenkov (ARICH) counter is installed in the forward end-cap region of the Belle II detector. The goal is to enhance the power of separation between kaons and pions up to and above 4σ for momenta up to 4 GeV/c, which is critical to the study of CP violation involved in B decays. The counter is made of aerogel tiles with refractive indices n of 1.045 and 1.055, transmission lengths of 30-40 mm, and dimensions of 18 × 18 × 2 cm3. A 144-channel HAPD (Hybrid Avalanche Photo Detector) is adopted as a photo-detector, and the HAPD signal processing is performed using ASICs (Application Specific Integrated Circuit) to digitize the signal and FPGAs (Field Programmable Gate Array) for data processing.During Phase II operation of SuperKEKB, the commissioning of ARICH is done both with cosmic rays and beam collisions. The Cherenkov rings are clearly observed, and the performance of the hardware system and identification algorithm is being evaluated. In this paper, we will report on the construction of ARICH and on the initial performance of the detector obtained during the commissioning

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

International audienceA 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

Initial performance of the Aerogel RICH detector of the Belle II experiment

International audienceThe Belle II experiment is a new generation B factory experiment at the SuperKEKB electron–positron collider. The main purpose of the experiment is to search for new physics with a large sample of B meson decays. The proximity-focusing Aerogel Ring-Imaging Cherenkov detector (ARICH) has been designed to identify kaons and pions in the forward end-cap of the Belle II spectrometer. Using aerogel as radiator with specialized photon sensors called HAPD, the K/ π separation is expected to reach more than 4 σ in the momentum range from 0.5 GeV/c to 4.0 GeV/c. ARICH detector was constructed in summer 2017 and was installed in the Belle II spectrometer in the beam line of the SuperKEKB collider. The test of the ARICH detector is performed using both cosmic rays and the beam collisions during the accelerator commissioning. We observe Cherenkov rings in the ARICH detector associated with charged tracks detected by the tracking system. The reconstructed Cherenkov angle distribution has a clear and reasonable peak. The ARICH K∕π separation performance is evaluated using Bhabha events in beam runs; the separation power achieve the design value

Belle II aerogel RICH detector

International audienceThe aerogel Ring Imaging CHerenkov counter (ARICH) is the particle identification device installed in the forward region of the Belle II detector at the SuperKEKB accelerator facility in Japan. The first electron–positron collisions at SuperKEKB took place on April 26, 2018, during the so called phase 2 run. The measured performance of the detector based on recorded Bhabha events during phase 2 is presented. We measure a 14 mrad average angular resolution per photon and 10 photons per Bhabha electron in the [6–8] GeV/c momentum range

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

International audienceIn 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 evaluation of the aerogel RICH counter for the Belle II spectrometer using early beam collision data

International audienceThe Aerogel Ring Imaging Cherenkov (ARICH) counter serves as a particle identification device in the forward end-cap region of the Belle II spectrometer. It is capable of identifying pions and kaons with momenta up to |$4\>$|GeV|$\>$|c|$^{-1}$| by detecting Cherenkov photons emitted in the silica aerogel radiator. After the detector alignment and calibration of the probability density function, we evaluate the performance of the ARICH counter using early beam collision data. Event samples of |$D^{\ast +} \to D^0 \pi^+ (D^0 \to K^-\pi^+)$| were used to determine the |$\pi(K)$| efficiency and the |$K(\pi)$| misidentification probability. We found that the ARICH counter is capable of separating kaons from pions with an identification efficiency of |$93.5 \pm 0.6 \, \%$| at a pion misidentification probability of |$10.9 \pm 0.9 \, \%$|⁠. This paper describes the identification method of the counter and the evaluation of the performance during its early operation