SuperKEKB Research Articles

Alignment for the first precision measurements at Belle II

On March 25th 2019, the Belle II detector recorded the first collisions delivered by the SuperKEKB accelerator. This marked the beginning of the physics run with vertex detector. The vertex detector was aligned initially with cosmic ray tracks without magnetic field simultaneously with the drift chamber. The alignment method is based on Millepede II and the General Broken Lines track model and includes also the muon system or primary vertex position alignment. To control weak modes, we employ sensitive validation tools and various track samples can be used as alignment input, from straight cosmic tracks to mass-constrained decays. With increasing luminosity and experience, the alignment is approaching the target performance, crucial for the first physics analyses in the era of Super-BFactories. We will present the software framework for the detector calibration and alignment, the results from the first physics run and the prospects in view of the experience with the first data.

The Belle II Raw Data Management System

The Belle II experiment, a major upgrade of the previouse+e−asymmetric collider experiment Belle, is expected to produce tens of petabytes of data per year due to the luminosity increase from the upgraded SuperKEKB accelerator. The distributed computing system of the Belle II experiment plays a key role, storing and distributing data in a reliable way to be easily accessed and analyzed by more than 1000 collaborators. In particular, the Belle II Raw Data Management system has been developed with an aim to upload output files onto grid storage, register them into the file and metadata catalogs, and make two replicas of the full raw data set using the Belle II Distributed Data Management system. It has been implemented as an extension of DIRAC (Distributed Infrastructure with Remote Agent Control) and consists of a database, services, client and monitoring tools, and several agents that treat the data automatically. The first year of data taken with the Belle II full detector has been managed by the Belle II Raw Data Management system successfully. The design, current status, and performance are presented. Prospects for improvements towards the full luminosity data taking are also reviewed.

Belle II実験電磁カロリメータ用PIN-PD電流値モニターによるSuperKEKB加速器phase2運転の放射線量測定

Belle II実験電磁カロリメータ用PIN-PD電流値モニターによるSuperKEKB加速器phase2運転の放射線量測定

Run and slow control system of the Belle II silicon vertex detector

The Belle II Silicon Vertex Detector (SVD) was installed recently and has been prepared for physics run at SuperKEKB factory, Tsukuba, Japan. For a reliable operation and data taking of the SVD, a sophisticated and robust run and slow control system has been implemented, which utilizes the Experimental Physics and Industrial Control System (EPICS) framework. EPICS uses client/server and publish/subscribe techniques to communicate between the various sub-systems and computers. The information exchange between the different pieces of software and computers is done by process variables (PVs). These PVs are provided by input/output controllers (IOCs), which communicate and interface with the hardware components. The Belle II SVD slow and run control comprises five groups of subsystems, which are SVD DAQ controller, Flash ADC controller, environmental monitors and interlocks, power supplies and EPICS infrastructure services. In this paper we describe the tasks and the implementation of the individual sub-systems, the interaction between them and the global Belle II run and slow control as well as the first experience from commissioning and initial operation of the SuperKEKB accelerator.

Performance of the Belle II imaging Time-Of-Propagation (iTOP) detector in first collisions

The iTOP detector is a novel Cherenkov detector developed for barrel particle identification at Belle II, an upgrade of the previous Belle experiment at KEK. The SuperKEKB accelerator, an upgrade of KEKB, collides electrons and positrons with a design luminosity of 8⋅1035cm−2s−1. In order to exploit the high collision rate, Belle II has a trigger frequency of up to 30 kHz. The iTOP detector uses quartz bars as source of Cherenkov photons. The photons are reflected inside the bars until they hit photomultipliers at one end. The spatial distribution and precise arrival times of the detected photons are used to reconstruct the Cherenkov angle. The photon arrival times have to be measured with a resolution better than 100 ps to achieve a good pion–kaon separation. Microchannel plate photomultipliers together with dedicated high-speed electronics for 2.7 GSa/s waveform sampling are used to achieve this timing resolution. The iTOP detector consists of 16 modules with 512 channels each, in total the detector has 8192 channels. First collisions were recorded in spring 2018. A phase of physics operation with a ramp up to full luminosity starts in March 2019. The design of the iTOP detector is shown and experience and results from initial operation are discussed together with an outlook on future running conditions.

Belle II aerogel RICH detector

The 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.

Physics Prospects of Exotic and Conventional Bottomonia at Belle II

The Belle II experiment, being constructed at the KEK laboratory in Japan, is a substantial upgrade of the Belle detector. The construction of the SuperKEKB accelerator, which is the upgrade of the KEKB accelerator, has been just completed. It aims to collect 50 times more data than the existing B-Factory samples beginning in 2018. Belle II is uniquely positioned to study the so-called XYZ particles: heavy exotic hadrons consisting of more than three quarks. First discovered by Belle, the number of these particles is in the dozens now, which implies the emergence of a new category within quantum chromodynamics. This talk will present the capabilities of Belle II to explore exotic and conventional bottomonium physics. There will be a particular focus on the physics reach of the first data, where opportunities exist to make an immediate impact on the field.

Decay Chain Reconstruction at Belle II

The Belle II detector underwent commissioning in 2018. Featuring a state of the art vertex detector with innovative pixel sensors, it will record collisions of e+e-beams from the SuperKEKB accelerator which is slated to provide luminosities 40 times higher than KEKB.This will bring new opportunities and challenges for physicists seeking to perform precision measurements, as increasingly precise vertex position reconstruction and background rejection power is needed to take advantage of the unprecedented statistics provided.We discuss the vertex reconstruction techniques available that make such measurements possible and present an approach to particle decay reconstruction based on the global fit of the full decay chain, implemented using a Kalman Filter. This technique is especially well suited to the treatment of processes with neutral decays. It allows for improved background rejection, access to a larger number of decay modes and a flexible framework for consistent treatment of measurement uncertainties.

Belle II Experiment: Status and Physics Prospects

The Belle II experiment at the SuperKEKB energy-asymmetric e+e− collider is the second-generation B-factory experiment, which is successor to the former Belle experiment at the KEKB accelerator. The Belle II experiment is aiming to study new physics beyond the Standard Model with high precision measurements. The design luminosity of the SuperKEKB accelerator, is 8×1035cm−1s−1, 40 times greater than that of the KEKB accelerator and plans to collect an integrated luminosity of 50 ab−1. In 2018 April, the Belle II detector recorded the first collision events during phase 2 operation. In this contribution, we present some highlights from phase 2 operation and prospects for the early and future physics programs.

Calibration and Alignment Framework for the Belle II detector

The Belle II experiment [1] is approaching its first physics run in 2018. Its full capability to operate at the precision frontier will need not only excellent performance of the SuperKEKB accelerator and the detector, but also advanced calibration methods combined with data quality monitoring. To deliver data in a form suitable for analysis as soon as possible, an automated Calibration Framework (CAF) has been developed. The CAF integrates various calibration algorithms and their input collection methods for event-level data. It allows execution of the calibration workflow using different backends from local machines to a computing cluster, resolution of dependencies among algorithms, management of the produced calibration constants, and database access across possible iterations. One of the main algorithms fully integrated in the framework uses Millepede II [2] to solve a large minimization problem emerging in the track-based alignment and calibration of the pixel and strip detector, the central drift chamber, and the muon system. Advanced fitting tools are used to properly describe the detector material and magnetic field and include measurements of different sub-detectors into a single global fit performed by Millepede. This talk will present the design of the calibration framework, the integration of the Millepede calibration, and its current performance.

Three-dimensional fast tracker for the central drift chamber based level-1 trigger system in the Belle II experiment

The Belle II detector at the SuperKEKB accelerator has a level 1 trigger implemented in field-programmable gate arrays. Due to the high luminosity of the beam, a trigger that effectively rejects beam induced background is required. A three dimensional tracking algorithm for the level 1 trigger that uses the Belle II central drift chamber detector response is being developed to reduce the recorded beam background while having a high efficiency for physics of interest. In this paper, we describe the three dimensional track trigger that finds and fits track parameters which we developed.

The Belle II experiment: status and physics program

The Belle II experiment at the SuperKEKB asymmetric-energy e+e- collider in Japan aims to search for new physics in the flavour transitions in the quark and lepton sectors. The SuperKEKB accelerator will operate at the target instantaneous luminosity of 8 × 1035 s-1cm2. It requires a substantial upgrade of the detector subsystems which are expected to record 50 ab-1 of data. Such a huge data sample in clean background environment allows for probing signatures of new physics through suppressed flavour physics reactions and cross checks for deviations from the Standard Model measured at the LHCb experiment. Physics data taking at the Belle II experiment successfully started in April 2018.

Remote monitoring system for the cryogenic system of superconducting magnets in the SuperKEKB interaction region

A remote monitoring system was developed based on the software infrastructure of the Experimental Physics and Industrial Control System (EPICS) for the cryogenic system of superconducting magnets in the interaction region of the SuperKEKB accelerator. The SuperKEKB has been constructed to conduct high-energy physics experiments at KEK. These superconducting magnets consist of three apparatuses, the Belle II detector solenoid, and QCSL and QCSR accelerator magnets. They are each contained in three cryostats cooled by dedicated helium cryogenic systems. The monitoring system was developed to read data of the EX-8000, which is an integrated instrumentation system to control all cryogenic components. The monitoring system uses the I/O control tools of EPICS software for TCP/IP, archiving techniques using a relational database, and easy human-computer interface. Using this monitoring system, it is possible to remotely monitor all real-time data of the superconducting magnets and cryogenic systems. It is also convenient to share data among multiple groups.

Status of the calibration and alignment framework at the Belle II experiment

The Belle II detector at the Super KEKB e+e−collider plans to take first collision data in 2018. The monetary and CPU time costs associated with storing and processing the data mean that it is crucial for the detector components at Belle II to be calibrated quickly and accurately. A fast and accurate calibration system would allow the high level trigger to increase the efficiency of event selection, and can give users analysis-quality reconstruction promptly.A flexible framework to automate the fast production of calibration constants is being developed in the Belle II Analysis Software Framework (basf2). Detector experts only need to create two components from C++ base classes in order to use the automation system. The first collects data from Belle II event data files and outputs much smaller files to pass to the second component. This runs the main calibration algorithm to produce calibration constants ready for upload into the conditions database. A Python framework coordinates the input files, order of processing, and submission of jobs. Splitting the operation into collection and algorithm processing stages allows the framework to optionally parallelize the collection stage on a batch system.

The role of meson exchanges in light-by-light scattering

We discuss the role of meson exchange mechanisms in γγ→γγ scattering. Several pseudoscalar (π0, η, η′(958), ηc(1S), ηc(2S)), scalar (f0(500), f0(980), a0(980), f0(1370), χc0(1P)) and tensor (f2(1270), a2(1320), f2′(1525), f2(1565), a2(1700)) mesons are taken into account. We consider not only s-channel but also for the first time t- and u-channel meson exchange amplitudes corrected for off-shell effects including vertex form factors. We find that, depending on not well known vertex form factors, the meson exchange amplitudes interfere among themselves and could interfere with fermion-box amplitudes and modify the resulting cross sections. The meson contributions are shown as a function of collision energy as well as angular distributions are presented. Interesting interference effects separately for light pseudoscalar, scalar and tensor meson groups are discussed. The meson exchange contributions may be potentially important in the context of a measurement performed recently in ultraperipheral collisions of heavy ions by the ATLAS collaboration. The light-by-light interactions could be studied in future in electron–positron collisions by the Belle II at SuperKEKB accelerator.

Status of Belle II and Physics Prospects

The Belle II experiment is a new generation B factory experiment at KEK in Japan, whose aim is the search of New Physics in the rare B meson decays. The operation of the SuperKEKB accelerator has just been started and the tuning of the beam condition is in progress. The construction of the Belle II detector is smoothly going on to be prepared for the start of physics run in 2018. The physics program at the Belle II experiment is now being discussed in the framework of Belle II Theory Interface Platform (B2TIP). In this report, the latest status of the SuperKEKB accelerator and the Belle II detector is described. The prospects for the physics at Belle II are shown in the latter part based on the on-going discussion in B2TIP.

The beam test measurements of the Belle II vertex detector modules

The Belle II experiment designed to study CP Violation and Beyond Standard model physics at the decays of B-mesons is quickly approaching its first physics run with the SuperKEKB accelerator (Tsukuba, Japan) already under commissioning. To operate in the unique conditions of the Belle II experiment, its vertex detector (VXD) is a six layers silicon detector with two innermost layers of DEPFET active pixel modules and four layers of double-sided strip modules. A section of it will become a commissioning detector for the first collisions of the next-generation high luminosity B-factory. The same setup, from cooling services, mechanical support or sensors and front-end electronics to DAQ, including the software and alignment framework, is tested under an electron beam provided by DESY facilities. We present the basic characteristics of the pixel and strip modules and the setup under test, including software and alignment framework—as close to the final system as possible.

The Belle II imaging Time-of-Propagation (iTOP) detector

High precision flavor physics measurements are an essential complement to the direct searches for new physics at the LHC ATLAS and CMS experiments. Such measurements will be performed using the upgraded Belle II detector that will take data at the SuperKEKB accelerator. With 40x the luminosity of KEKB, the detector systems must operate efficiently at much higher rates than the original Belle detector. A central element of the upgrade is the barrel particle identification system. Belle II has built and installed an imaging-Time-of-Propagation (iTOP) detector. The iTOP uses quartz optics as Cherenkov radiators. The photons are transported down the quartz bars via total internal reflection with a spherical mirror at the forward end to reflect photons to the backward end where they are imaged onto an array of segmented Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMTs). The system is read out using giga-samples per second waveform sampling Application-Specific Integrated Circuits (ASICs). The combined timing and spatial distribution of the photons for each event are used to determine particle species. This paper provides an overview of the iTOP system.

The Belle II experiment: fundamental physics at the flavor frontier

After the major success of B-factories to establish the CKM mechanism and its proven potential to search for new physics, the Belle II experiment will continue exploring the physics at the flavor frontier over the next years. Belle II will collect 50 times more data than its predecessor, Belle, and allow for various precision measurements and searches of rare decays and particles. This paper introduces the B-factory concept and the flavor frontier approach to search for new physics. It then describes the SuperKEKB accelerator and the Belle II detector, as well as some of the physics that will be analyzed in Belle II, concluding with the experiment status and schedule.

Belle II Software

Belle II is a next generation B factory experiment that will collect 50 times more data than its predecessor, Belle. The higher luminosity at the SuperKEKB accelerator leads to higher background levels and requires a major upgrade of the detector. As a consequence, the simulation, reconstruction, and analysis software must also be upgraded substantially. Most of the software has been redesigned from scratch, taking into account the experience from Belle and other experiments and utilizing new technologies. The large amount of experimental and simulated data requires a high level of reliability and reproducibility, even in parallel environments. Several technologies, tools, and organizational measures are employed to evaluate and monitor the performance of the software during development.