SuperKEKB collider Akai, Kazunori; Furukawa, Kazuro; Koiso, Haruyo
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2018, Volume:
907
Journal Article
Peer reviewed
Open access
SuperKEKB, a 7 GeV electron – 4 GeV positron double-ring collider, is constructed by upgrading KEKB in order to seek new physics beyond the Standard Model. The design luminosity of SuperKEKB is ...8×1035cm−2s−1—40 times higher than that achieved by KEKB. The greater part of the gain comes from significantly decreasing the beam sizes at the interaction point based on the nanobeam collision scheme; the design beam currents in both rings are double those achieved in KEKB. Large-scale construction to upgrade both the collider rings and the injector was conducted, and beam commissioning without the Belle II detector and final-focus magnets was successfully carried out from February to June in 2016. Subsequently, renovation of the interaction region, including the installation of the final-focus magnets and Belle II, and construction in the final stage of a new positron damping ring were conducted. Having completed the interaction region, beam collision tuning is scheduled from March till July in 2018. This paper reviews the design, construction, and beam commissioning of SuperKEKB.
Measurements of beam backgrounds in SuperKEKB Phase 2 Liptak, Z.; Paladino, A.; Santelj, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2022, Volume:
1040
Journal Article
Peer reviewed
Open access
The high design luminosity of the SuperKEKB electron–positron collider will result in challenging levels of beam-induced backgrounds in the interaction region. Understanding and mitigating these ...backgrounds is critical to the success of the Belle II experiment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKEKB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also report on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions from synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds originating from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV electron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds forward and conclude it is safe to install the Belle II vertex detector.
The process with the center-of-mass (CM) energy in the range from 3.7 to 10.6 GeV is calculated up to the next-to-leading order (NLO) in quantum chromodynamics (QCD). At 10.6 GeV, the result is ...consistent with the experimental result from Belle. However, the predictions are much smaller than the background in the measurements at BESIII in the low CM energy range from 3.7 to 4.6 GeV. This indicates that the convergence of the QCD perturbative expansion becomes worse as the CM energy is closer to the inclusive production threshold. For a further study of the QCD mechanism of production in collisions with different CM energies, the initial state radiation effect of and are calculated in QCD NLO. The results are plotted and the number of events for different CM energy bins are provided for SuperKEKB. This provides a method to precisely test the validity of perturbative predictions for production in future measurements.
SuperKEKB beam final focus superconducting magnet system Ohuchi, N.; Arimoto, Y.; Akai, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2021, Volume:
1021
Journal Article
Peer reviewed
Open access
The SuperKEKB was designed and constructed as the upgraded accelerator of KEKB. In this accelerator design, the nano-beam scheme of collision was applied and a luminosity of 8 x1035 cm-2s-1 was ...targeted. In the design, the beam final focus system was the key component in the accelerator hardware elements. This final focus system consists of 55 superconducting magnets. In this paper, the designs of the magnets, the cryostats and the cryogenic system are shown, and the field measurement results are reported. The SuperKEKB beam operation with the final focus system started on 2018 March 19, and the magnet quench events up to 2020 December 16 are described.
•SuperKEKB accelerator superconducting magnets and cryostat are introduced.•Cooling schemes of subcooled and saturated liquid helium are compared.•Cryogenic cool-down and steady processes were ...studied and monitored.•Cryostat thermal performance was evaluated with various methods.
SuperKEKB is a particle accelerator to collide electron and positron beams and employs 55 superconducting (SC) magnets which are accommodated in two cryostats and cooled by subcooled liquid helium (LHe) of ∼ 20 g/s from refrigerators. One cryostat was set up in laboratory for exciting tests and cooled by continuous flow of saturated LHe (<3.0 g/s) from dewars of 1000 L. The differences of two cooling schemes of subcooled and saturated LHe were investigated and described in this paper. The required liquids to cool down the cryostat cold mass (>1700 kg) to 4.5 K were evaluated with a quantified utilization of vapor sensible heat, which fills the large gap between the maximum and minimum liquid requirement presented in most cryogenic literature. The saturated LHe flow was computed to ensure LHe accumulation in the cryostat and immerse SC magnets. The cryogenic processes were monitored by the measured cryogenic temperatures, pressures, flow rates and resistances of SC magnets, which demonstrate cryogenic stabilities with two-phase helium flow and illustrate the agreements with the thermal studies and analyses. This study provides a successful experience to cool SC magnet cryostats of large cold mass with continuous flow of saturated LHe from dewars instead of cryogenic refrigerators.
SuperKEKB beam final focus superconducting magnet system Ohuchi, N.; Arimoto, Y.; Akai, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2022, Volume:
1021
Journal Article
Peer reviewed
Open access
The SuperKEKB was designed and constructed as the upgraded accelerator of KEKB. In this accelerator design, the nano-beam scheme of collision was applied and a luminosity of 8 × 1035 cm−2s−1 was ...targeted. In the design, the beam final focus system was the key component in the accelerator hardware elements. This final focus system consists of 55 superconducting magnets. In this paper, the designs of the magnets, the cryostats and the cryogenic system are shown, and the field measurement results are reported. The SuperKEKB beam operation with the final focus system started on 2018 March 19, and the magnet quench events up to 2020 December 16 are described.
Detectors for extreme luminosity: Belle II Adachi, I.; Browder, T.E.; Križan, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2018, Volume:
907
Journal Article
Peer reviewed
We describe the Belle II detector at the SuperKEKB electron–positron accelerator. SuperKEKB operates at the energy of the ϒ(4S) resonance where pairs of B mesons are produced in a coherent quantum ...mechanical state with no additional particles. Belle II, the first Super B factory detector, aims to achieve performance comparable to the original Belle and BaBar B factory experiments, which first measured the large CP violating effects in the B meson system, with much higher luminosity collisions and larger beam-induced backgrounds.
The Belle II experiment at the SuperKEKB energy-asymmetric e+e− collider is the upgraded successor of the B-factory facility at the KEK laboratory, Japan. The designed instantaneous luminosity of the ...machine is 6×1035cm−2s−1. The Belle II experiment aims to ultimately accumulate 50 ab−1 of data, 50 times more than its predecessor. With this data set, Belle II will be able to measure the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements with unprecedented precision and explore flavor physics with B and D mesons and τ leptons. Belle II has also a unique capability to search for low-mass dark matter and low-mass mediators. Here, we briefly report the latest results from Belle II.
A neural network for beam background decomposition in Belle II at SuperKEKB Schwenker, B.; Herzberg, L.; Buch, Y. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
April 2023, 2023-04-00, 2023-04-01, Volume:
1049, Issue:
C
Journal Article
Peer reviewed
Open access
We describe a neural network for predicting the background hit rate in the Belle II detector produced by the SuperKEKB electron–positron collider. The neural network, BGNet, learns to predict the ...individual contributions of different physical background sources, such as beam-gas scattering or continuous top-up injections into the collider, to Belle II sub-detector rates. The samples for learning are archived 1Hz time series of diagnostic variables from the SuperKEKB collider subsystems and measured hit rates of Belle II used as regression targets. We test the learned model by predicting detector hit rates on archived data from different run periods not used during training. We show that a feature attribution method can help interpret the source of changes in the background level over time.
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