Using the full data sample collected with the Belle detector at the KEKB asymmetric-energy e+e- collider, we present three recent measurements of time-dependent CP violation in B decays that are ...sensitive to potential new physics contributions and a measurement of branching fraction of the B0 → π0π0 decay. We studied B → ωK decays and measured the values of CP violation parameters in B0 → ωK0S to be AωK0S = 0.36 ± 0.19 ± 0.05 and SωK0S = +0.91 ± 0.32 ± 0.05, which gives the first evidence of CP violation in this decay. From the measurement of CP violation parameters in the B0 → η'K0 decay we obtain Sη'K0 = 0.68 ± 0.07 ± 0.03 and Aη'K0 = +0.03 ± 0.05 ± 0.04, which are the world's most precise values to date. We present the Belle first measurement of CP violation parameters in B0 → K0Sηγ decay, where we measure SK0Sηγ = -1.32 ± 0.77 ± 0.36 and AK0Sηγ = -0.48 ± 0.41 ± 0.07 (preliminary). Finally we present our preliminary measurement of the B0 → π0π0 branching fraction. We measure B(B0 → π0π0) = (0.89 ± 0.12 ± 0.10) × 10-6, with significantly improved sensitivity compared to previously available results.
On-detector digital electronics in high-energy physics (HEP) experiments is increasingly being implemented by means of static random access memory (SRAM)-based field programmable gate arrays (FPGAs), ...due to their reconfigurability, fast data processing, and transfer. Radiation-induced single-event upsets (SEUs) in the configuration hinder the correct operation, since they may alter the programmed routing paths and logic functions. In most data acquisition systems, data from clustered front-end modules are aggregated by a single board, which then transmits data to off-detector electronics for acquisition and triggering. In this work, we present a novel scrubber capable of correcting radiation-induced upsets in the configuration of SRAM-based FPGAs by majority voting across clustered modules. We designed it for the Aerogel Ring Imaging CHerenkov (ARICH) counter of the Belle II experiment at the KEK Laboratory, Tsukuba, Japan. We discuss the architecture of the system and its implementation in a Virtex-5 FPGA, in the aggregator board, for correcting the configuration of up to six Spartan-6 LX45 FPGAs, on pertaining front-end modules. We discuss results from neutron irradiation tests at the TRIGA reactor of the Jožef Stefan Institute, Ljubljana, Slovenia, which show that our solution corrects an average of 6.2 k upsets in each target FPGA before the failure of the scrubber. Moreover, with respect to the Xilinx soft error mitigation (SEM) controller, our design improved the mean time before failure of data readout by 30%.
In the forward end-cap of the Belle II spectrometer, particle identification is provided by a proximity focusing RICH detector with an aerogel radiator (ARICH). The ARICH’s primary function is to ...effectively distinguish between pions and kaons in the momentum range of 0.5GeV/c to about 4GeV/c, as well as to contribute to identification of low-momentum leptons. Since its operation began, Belle II has collected over 420fb−1 of data. Based on this large data sample, studies of several effects that impact the performance of the ARICH detector were carried out. In this paper, we present a comparison of the observed Cherenkov ring image and detector particle identification performance in the measured data and detector simulation. Furthermore, we highlight recent efforts aimed at enhancing the ARICH’s performance by taking into account the effects of particle decay in flight and scattering in materials before the detector, as well as by refining the probability density function used for particle identification likelihood evaluation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
4.
Test of the HAPD light sensor for the Belle II Aerogel RICH Yusa, Y.; Adachi, I.; Dolenec, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2017, Volume:
876
Journal Article
Peer reviewed
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
5.
Aerogel RICH for the Belle II forward PID Nishida, S.; Adachi, I.; Hamada, N. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2014, Volume:
766
Journal Article
Peer reviewed
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 4 sigma separation of pions and kaons up to momenta of 4 GeV/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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The 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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
7.
Front-end electronics of the Belle II aerogel ring imaging detector Pestotnik, R.; Adachi, I.; Burmistrov, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Volume:
952
Journal Article
Peer reviewed
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
8.
A 144-channel HAPD for the Aerogel RICH at Belle II Korpar, S.; Adachi, I.; Hamada, N. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2014, Volume:
766
Journal Article
Peer reviewed
A hybrid photo-detector (HAPD) has been developed for the aerogel RICH (ARICH) of the Belle II experiment. In the present contribution we report the performance tests in magnetic fields, results of ...the neutron and gamma irradiation studies, and of aging tests. We also review the production status and plans.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
Aerogel RICH for forward PID at Belle II Pestotnik, R.; Adachi, I.; Hara, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2013, Volume:
732
Journal Article
Peer reviewed
For the Belle II spectrometer we are preparing a proximity focusing RICH with aerogel as the radiator. It will be positioned in the forward direction of the spectrometer in the small space between ...the drift chamber and the electromagnetic calorimeter inside a strong magnetic field of 1.5T. The Hybrid Avalanche Photo Diode used as a photo sensor, is able to detect single photons with a high efficiency, can operate in the magnetic field and is resistant to the expected neutron and gamma fluxes in the detector. By detecting more than 11 photons per incident 4GeV/c pion, with 15mrad single photon Cherenkov angle resolution, the designed aerogel RICH should enable an efficient separation of kaons from pions in the wide range of particle momenta from 0.5GeV/c up to 4GeV/c.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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