Recent developments in data reconstruction for aerogel RICH at Belle II

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 0.5 GeV/c to about 4 GeV/c, as well as to contribute to identification of low-momentum leptons. Since its operation began, Belle II has collected over 420 fb-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.Comment: 4 pages, 7 figures. Poster contribution to 11th International Workshop on Ring Imaging Cherenkov Detectors (RICH2022), September 12-16 2022. Submitted to Nuclear Inst. and Methods in Physics Research,

The Aerogel RICH detector of the Belle II experiment

International audienceIn the forward end-cap of the Belle II spectrometer, an innovative proximity focusing Ring Imaging Cherenkov counter with a multilayer focusing aerogel radiator has been installed. The detector is designed to be operated in a magentic field of 1.5 T, and consists of a double layer aerogel radiator, an expansion volume and a photon detector. In total 420 Hamamatsu hybrid avalanche photo sensors with 144 channels each are used to read out single Cherenkov photons with high efficiency. We expect the device to provide better than 4s separation of pions from kaons in the full kinmatic region of the experiment, from 0.5 GeV/c to 4 GeV/c. The detector components have been successfully produced and installed in the spectrometer. After the commissioning phase in 2018, the detector is now included in the Belle II data taking, and is expected to contribute substantially to the performance of the spectrometer in looking for rare decays of B and D mesons, and of tau leptons. In this contribution we review the detector design and present results of the first detector performance studies

Measurements of Beam Backgrounds in SuperKEKB Phase 2

The high design luminosity of the SuperKEKB electron-positron collider will result in challenging levels of beam-induced backgro unds in the interaction region. Understanding and mitigating these backgrounds is critical to the success of the Belle~II experi ment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKE KB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also repor t on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions f rom synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds origina ting from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV elect ron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds for ward and conclude it is safe to install the Belle II vertex detector

The ECFA Early Career Researcher's Panel: composition, structure, and activities, 2021 -- 2022

The European Committee for Future Accelerators (ECFA) Early Career Researcher's (ECR) panel, which represents the interests of the ECR community to ECFA, officially began its activities in January 2021. In the first two years, the panel has defined its own internal structure, responded to ECFA requests for feedback, and launched its own initiatives to better understand and support the diverse interests of early career researchers. This report summarises the panel composition and structure, as well as the different activities the panel has been involved with during the first two years of its existence

The ECFA Early Career Researcher's Panel: composition, structure, and activities, 2021 -- 2022

The European Committee for Future Accelerators (ECFA) Early Career Researcher's (ECR) panel, which represents the interests of the ECR community to ECFA, officially began its activities in January 2021. In the first two years, the panel has defined its own internal structure, responded to ECFA requests for feedback, and launched its own initiatives to better understand and support the diverse interests of early career researchers. This report summarises the panel composition and structure, as well as the different activities the panel has been involved with during the first two years of its existence

The ECFA Early Career Researcher's Panel: composition, structure, and activities, 2021 -- 2022

The European Committee for Future Accelerators (ECFA) Early Career Researcher's (ECR) panel, which represents the interests of the ECR community to ECFA, officially began its activities in January 2021. In the first two years, the panel has defined its own internal structure, responded to ECFA requests for feedback, and launched its own initiatives to better understand and support the diverse interests of early career researchers. This report summarises the panel composition and structure, as well as the different activities the panel has been involved with during the first two years of its existence

The ECFA Early Career Researcher's Panel: composition, structure, and activities, 2021 -- 2022

The European Committee for Future Accelerators (ECFA) Early Career Researcher's (ECR) panel, which represents the interests of the ECR community to ECFA, officially began its activities in January 2021. In the first two years, the panel has defined its own internal structure, responded to ECFA requests for feedback, and launched its own initiatives to better understand and support the diverse interests of early career researchers. This report summarises the panel composition and structure, as well as the different activities the panel has been involved with during the first two years of its existence

Data quality monitors of vertex detectors at the start of the Belle II experiment

The Belle II experiment features a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric e+e− collider at KEK in Tsukuba, Japan. The accelerator completed its first phase of commissioning in 2016, and the Belle II detector saw its first electron-positron collisions in April 2018. Belle II features a newly designed silicon vertex detector based on double-sided strip layers and DEPFET pixel layers. A subset of the vertex detector was operated in 2018 to determine background conditions (Phase 2 operation). The collaboration completed full detector installation in January 2019, and the experiment started full data taking. This paper will report on the final arrangement of the silicon vertex detector part of Belle II with a focus on online monitoring of detector conditions and data quality, on the design and use of diagnostic and reference plots, and on integration with the software framework of Belle II. Data quality monitoring plots will be discussed with a focus on simulation and acquired cosmic and collision data

Measurement of the branching fractions for Cabibbo-suppressed decays D+→K+K−π+π0D^{+}\to K^{+} K^{-}\pi^{+}\pi^{0} and D(s)+→K+π−π+π0D_{(s)}^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0} at Belle

International audienceWe present measurements of the branching fractions for the singly Cabibbo-suppressed decays $D^+\to K^{+}K^{-}\pi^{+}\pi^{0}$ and $D_s^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0}$, and the doubly Cabibbo-suppressed decay $D^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0}$, based on 980 ${\rm fb}^{-1}$ of data recorded by the Belle experiment at the KEKB $e^{+}e^{-}$ collider. We measure these modes relative to the Cabibbo-favored modes $D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}$ and $D_s^{+}\to K^{+}K^{-}\pi^{+}\pi^{0}$. Our results for the ratios of branching fractions are $B(D^{+}\to K^{+}K^{-}\pi^{+}\pi^{0})/B(D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}) = (11.32 \pm 0.13 \pm 0.26)\%$, $B(D^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0})/B(D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0}) = (1.68 \pm 0.11\pm 0.03)\%$, and $B(D_s^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0})/B(D_s^{+}\to K^{+}K^{-}\pi^{+}\pi^{0}) = (17.13 \pm 0.62 \pm 0.51)\%$, where the uncertainties are statistical and systematic, respectively. The second value corresponds to $(5.83\pm 0.42)\times\tan^4\theta_C$, where $\theta_C$ is the Cabibbo angle; this value is larger than other measured ratios of branching fractions for a doubly Cabibbo-suppressed charm decay to a Cabibbo-favored decay. Multiplying these results by world average values for $B(D^{+}\to K^{-}\pi^{+}\pi^{+}\pi^{0})$ and $B(D_s^{+}\to K^{+}K^{-}\pi^{+}\pi^{0})$ yields $B(D^{+}\to K^{+}K^{-}\pi^{+}\pi^{0})= (7.08\pm 0.08\pm 0.16\pm 0.20)\times10^{-3}$, $B(D^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0})= (1.05\pm 0.07\pm 0.02\pm 0.03)\times10^{-3}$, and $B(D_s^{+}\to K^{+}\pi^{-}\pi^{+}\pi^{0}) = (9.44\pm 0.34\pm 0.28\pm 0.32)\times10^{-3}$, where the third uncertainty is due to the branching fraction of the normalization mode. The first two results are consistent with, but more precise than, the current world averages. The last result is the first measurement of this branching fraction