Machine learning has become a popular instrument for the search of undiscovered particles and mechanisms at particle collider experiments. It enables the investigation of large datasets and is ...therefore suitable to operate directly on minimally-processed data coming from the detector instead of reconstructed objects. Here, we study patterns of raw pixel hits recorded by the Belle II pixel detector, that is operational since 2019 and presently features 4 M pixels and trigger rates up to 5 kHz. In particular, we focus on unsupervised techniques that operate without the need for a theoretical model. These model-agnostic approaches allow for an unbiased exploration of data while filtering out anomalous detector signatures that could hint at new physics scenarios. We present the identification of hypothetical magnetic monopoles against Belle II beam background using self-organizing kohonen maps and autoencoders. These two unsupervised algorithms are compared to a Multilayer Perceptron and a superior signal efficiency of the Autoencoder is found at high background-rejection levels. Our results strengthen the case for using unsupervised machine learning techniques to complement traditional search strategies at particle colliders and pave the way to potential online applications of the algorithms in the near future.
Nachdem die Vertikal-Gruppenfreistellungsverordnung 330/2010 (i. F. VGVO 2010) und die dazugehörigen Leitlinien (i. F. V-LL 2010) seinerzeit nur wenige Änderungen zu ihren Vorgängerversionen ...aufwiesen, stellen die Vertikal-Gruppenfreistellungsverordnung 2022/720 (i. F. Vertikal-GVO) sowie die diesbezüglichen Leitlinien (i. F. Leitlinien) eine tiefgreifendere Reform dar. Zwar haben die Leitlinien massiv an Umfang zugenommen, allerdings ist die Verordnung insgesamt praxisnäher geworden und gibt klarere Hinweise für eine Vielzahl von Einzelproblemen in Handels- und Liefervereinbarungen. Der Beitrag soll wichtige Änderungen im Lichte der Gesetzgebungshistorie aufzeigen und einordnen.
Zusammenfassung
Nachdem die Vertikal-Gruppenfreistellungsverordnung 330/2010 (i. F. VGVO 2010) und die dazugehörigen Leitlinien (i. F. V-LL 2010) seinerzeit nur wenige Änderungen zu ihren ...Vorgängerversionen aufwiesen, stellen die Vertikal-Gruppenfreistellungsverordnung 2022/720 (i. F. Vertikal-GVO) sowie die diesbezüglichen Leitlinien (i. F. Leitlinien) eine tiefgreifendere Reform dar. Zwar haben die Leitlinien massiv an Umfang zugenommen, allerdings ist die Verordnung insgesamt praxisnäher geworden und gibt klarere Hinweise für eine Vielzahl von Einzelproblemen in Handels- und Liefervereinbarungen. Der Beitrag soll wichtige Änderungen im Lichte der Gesetzgebungshistorie aufzeigen und einordnen.
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, Letnik:
1040
Journal Article
Recenzirano
Odprti dostop
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.
Track finding at Belle II Bertacchi, Valerio; Bilka, Tadeas; Braun, Nils ...
Computer physics communications,
02/2021, Letnik:
259
Journal Article
Recenzirano
Odprti dostop
This paper describes the track-finding algorithm that is used for event reconstruction in the Belle II experiment operating at the SuperKEKB B-factory in Tsukuba, Japan. The algorithm is designed to ...balance the requirements of a high efficiency to find charged particles with a good track parameter resolution, a low rate of spurious tracks, and a reasonable demand on CPU resources. The software is implemented in a flexible, modular manner and employs a diverse selection of global and local track-finding algorithms to achieve an optimal performance.
For the Belle II experiment at KEK (Tsukuba, Japan) the KEKB accelerator was upgraded to deliver a 40 times larger instantaneous luminosity than before, which requires an increased radiation hardness ...of the detector components. As the innermost part of the Belle II detector, the pixel detector (PXD), based on DEPFET (DEpleted P-channel Field Effect Transistor) technology, is most exposed to radiation from the accelerator. An irradiation campaign was performed to verify that the PXD can cope with the expected amount of radiation. We present the results of this measurement campaign in which an X-ray machine was used to irradiate a single PXD half-ladder to a total dose of 266kGy. The half-ladder is from the same batch as the half-ladders used for Belle II. According to simulations, the total accumulated dose corresponds to 7–10 years of Belle II operation. While individual components have been irradiated before, this campaign is the first full system irradiation. We discuss the effects on the DEPFET sensors, as well as the performance of the front-end electronics. In addition, we present efficiency studies of the half-ladder from beam tests performed before and after the irradiation.
High-voltage particle detectors in commercial CMOS technologies are a detector family that allows implementation of low-cost, thin and radiation-tolerant detectors with a high time resolution. In the ...R/D phase of the development, a radiation tolerance of 1015neq/cm2, nearly 100% detection efficiency and a spatial resolution of about 3μm were demonstrated. Since 2011 the HV detectors have first applications: the technology is presently the main option for the pixel detector of the planned Mu3e experiment at PSI (Switzerland). Several prototype sensors have been designed in a standard 180nm HV CMOS process and successfully tested. Thanks to its high radiation tolerance, the HV detectors are also seen at CERN as a promising alternative to the standard options for ATLAS upgrade and CLIC. In order to test the concept, within ATLAS upgrade R/D, we are currently exploring an active pixel detector demonstrator HV2FEI4; also implemented in the 180nm HV process.
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 experiment features a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric
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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.
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