228 research outputs found
The new two-layer Belle II PiXel Detector
No full textAbstract The Belle II experiment [1] at SuperKEKB [2] has been collecting data from asymmetric-energy e + e - collisions at the Υ(4S) resonance at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, since 2019. Its goal is to collect a BB̅ data set 50 times larger than those of its predecessors, Belle and BaBar, enabling unprecedented precision in the measurement of Standard Model processes and the search for new physics at the luminosity frontier. To achieve this, a vertex resolution on the order of 30 μm is required for precise discrimination of decay vertices and lifetime measurements of short-lived particles. This precision is achieved by the Belle II VerteX Detector (VXD), which consists of the ultra-low-mass PiXel Detector (PXD) based on DEpleted P-channel Field Effect Transistor (DEPFET) technology [3], surrounded by a double-sided silicon strip detector (SVD) [4]. A partially equipped PXD used for data taking period until 2022 (Run 1) has been replaced in 2023 by a new fully populated PXD. This PXD is used for the current data taking period (Run 2), which started in 2024. This article summarizes the commissioning and the first operation experience of the newly installed PXD
Combined analysis of Belle and Belle II data to determine the CKM angle φ3 using B+ → D(h+h−)h+ decays
No full textThe Belle II vertex detector integration
No full textBelle II DEPFET, PXD, and SVD Collaborations: et al.The Belle II experiment comes with a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric ee collider with energies tuned to ϒ(4S) resonance s=10.588 GeV. The accelerator has successfully completed the first phase of commissioning in 2016 and the first electron–positron collisions in Belle II took place in April 2018. Belle II features a newly designed silicon vertex detector based on DEPFET pixel and double-sided strip layers. Currently, a subset of the vertex detector is installed (Phase 2 of the experiment). Installation of the full detector (Phase 3) will be completed by the end of 2018. This paper describes the Phase 2 arrangement of the Belle II silicon vertex detector, with focus on the interconnection of detectors and their integration with the software framework of Belle II. Alignment issues are discussed based on detector simulations and first acquired data.This work is supported by MSCA-RISE, European Union project JENNIFER (EU grant n. 644294), MEXT, Japan, WPI, and JSPS (Japan); ARC (Australia); BMWFW (Austria); MSMT, Czech Republic, GAUK 404316 (Czech Republic); AIDA-2020 (Germany); DAE, India and DST (India); INFN (Italy); NRF-2016K1A3A7A09005605 and RSRI (Korea); MNiSW (Poland); Federal Ministry of Education and Research (BMBF, Germany); and MINECO, Spain grant FPA2015-71292-C2-1-P (Spain)
Search for the decay B0→γγ using Belle and Belle II data
No full textWe report the result of a search for the rare decay B0 → γγ using a combined dataset of 753 × 10^6 BB̄ pairs collected by the Belle experiment and 387 × 106 BB̄ pairs collected by the Belle II experiment from decays of the Y(4S) resonance produced in e+e- collisions. A simultaneous fit to the Belle and Belle II data set yields 11.0+6.5-5.5 signal events, corresponding to a 2.5σ significance. We determine the branching fraction B( B0 → γγ ) = ( 3.7 +2.2-1.8 (stat) ±0.5 (syst) ) 10^-8 and set a 90% credibility level upper limit of B( B0 → γγ ) < 6.4 10^-8
Determination of the CKM angle ϕ 3 from a combination of Belle and Belle II results
No full textAbstract We report a determination of the CKM angle ϕ 3, also known as γ, from a combination of measurements using samples of up to 711 fb −1 from the Belle experiment and up to 362 fb −1 from the Belle II experiment. We combine results from analyses of B + → DK +, B + → Dπ +, and B + → D * K + decays, where D is an admixture of D 0 and D ¯ 0 mesons, in a likelihood fit to obtain ϕ 3 = (75.2 ± 7.6) ° . We also briefly discuss the interpretation of this result
Mesure de l’asymétrie CP dépendante du temps pour les désintégrations B en K*gamma avec l’expérience Belle II
No full textThe Standard Model of particle physics, which describes the fundamental particles and their interactions, is the most successful theory in the history of science. For decades it has been tested by numerous scientific collaborations with great success. However, the theory is incomplete. In order to find evidence of physics beyond the Standard Model, the experiments are upgraded to gather more and more data with higher accuracy. This thesis presents the proposition of a new vertex detector for the Belle II experiment, along with its software implementation. With Belle, this thesis presents a new time-dependent measurement of the CP violation with B^0→K_S^0 π^+ π^- γ, which can improve the constrains on some Standard Model parameters. With Belle II, the rediscovery of B^0→K_S^0 π^+ π^- γ and the branching fraction measurement of B^0→K_S^0 π^0 γ with around 190 fb-1 is described. The result of B(B^0→K_S^0 π^0 γ)=(7.28±1.75(stat)±1.03(syst))×〖10〗^(-6) is compatible with the predictions.Le modèle standard de physique des particules, qui décrit les particules fondamentales et leurs interactions, est la théorie la plus réussie de l'histoire de la science. Pendant des décennies, il a été testé par de nombreuses collaborations scientifiques avec succès. Cependant, la théorie est incomplète. Afin de trouver des preuves de physique au-delà du modèle standard, les expériences sont améliorées pour recueillir de plus en plus de données avec une précision de plus en plus élevée. Cette thèse présente la proposition d'un nouveau détecteur de vertex pour l'expérience Belle II, ainsi que son implémentation logicielle. Avec Belle, cette thèse présente une nouvelle mesure dépendant du temps de la violation CP avec B^0→K_S^0 π^+ π^- γ , qui peut améliorer les contraintes de certains paramètres du modèle standard. Avec Belle II, la redécouverte de B^0→K_S^0 π^+ π^- γ et la mesure du rapport d'embranchement de B^0→K_S^0 π^0 γ avec environ 190 fb-1 sont décrites. Le résultat de B(B^0→K_S^0 π^0 γ)=(7.28±1.75(stat)±1.03(syst))×〖10〗^(-6) est compatible avec les prédictions
Mesure de l’asymétrie CP dépendante du temps pour les désintégrations B en K*gamma avec l’expérience Belle II
No full textThe Standard Model of particle physics, which describes the fundamental particles and their interactions, is the most successful theory in the history of science. For decades it has been tested by numerous scientific collaborations with great success. However, the theory is incomplete. In order to find evidence of physics beyond the Standard Model, the experiments are upgraded to gather more and more data with higher accuracy. This thesis presents the proposition of a new vertex detector for the Belle II experiment, along with its software implementation. With Belle, this thesis presents a new time-dependent measurement of the CP violation with B^0→K_S^0 π^+ π^- γ, which can improve the constrains on some Standard Model parameters. With Belle II, the rediscovery of B^0→K_S^0 π^+ π^- γ and the branching fraction measurement of B^0→K_S^0 π^0 γ with around 190 fb-1 is described. The result of B(B^0→K_S^0 π^0 γ)=(7.28±1.75(stat)±1.03(syst))×〖10〗^(-6) is compatible with the predictions.Le modèle standard de physique des particules, qui décrit les particules fondamentales et leurs interactions, est la théorie la plus réussie de l'histoire de la science. Pendant des décennies, il a été testé par de nombreuses collaborations scientifiques avec succès. Cependant, la théorie est incomplète. Afin de trouver des preuves de physique au-delà du modèle standard, les expériences sont améliorées pour recueillir de plus en plus de données avec une précision de plus en plus élevée. Cette thèse présente la proposition d'un nouveau détecteur de vertex pour l'expérience Belle II, ainsi que son implémentation logicielle. Avec Belle, cette thèse présente une nouvelle mesure dépendant du temps de la violation CP avec B^0→K_S^0 π^+ π^- γ , qui peut améliorer les contraintes de certains paramètres du modèle standard. Avec Belle II, la redécouverte de B^0→K_S^0 π^+ π^- γ et la mesure du rapport d'embranchement de B^0→K_S^0 π^0 γ avec environ 190 fb-1 sont décrites. Le résultat de B(B^0→K_S^0 π^0 γ)=(7.28±1.75(stat)±1.03(syst))×〖10〗^(-6) est compatible avec les prédictions
Mesure de l’asymétrie CP dépendante du temps pour les désintégrations B en K*gamma avec l’expérience Belle II
No full textLe modèle standard de physique des particules, qui décrit les particules fondamentales et leurs interactions, est la théorie la plus réussie de l'histoire de la science. Pendant des décennies, il a été testé par de nombreuses collaborations scientifiques avec succès. Cependant, la théorie est incomplète. Afin de trouver des preuves de physique au-delà du modèle standard, les expériences sont améliorées pour recueillir de plus en plus de données avec une précision de plus en plus élevée. Cette thèse présente la proposition d'un nouveau détecteur de vertex pour l'expérience Belle II, ainsi que son implémentation logicielle. Avec Belle, cette thèse présente une nouvelle mesure dépendant du temps de la violation CP avec B^0→K_S^0 π^+ π^- γ , qui peut améliorer les contraintes de certains paramètres du modèle standard. Avec Belle II, la redécouverte de B^0→K_S^0 π^+ π^- γ et la mesure du rapport d'embranchement de B^0→K_S^0 π^0 γ avec environ 190 fb-1 sont décrites. Le résultat de B(B^0→K_S^0 π^0 γ)=(7.28±1.75(stat)±1.03(syst))×〖10〗^(-6) est compatible avec les prédictions.The Standard Model of particle physics, which describes the fundamental particles and their interactions, is the most successful theory in the history of science. For decades it has been tested by numerous scientific collaborations with great success. However, the theory is incomplete. In order to find evidence of physics beyond the Standard Model, the experiments are upgraded to gather more and more data with higher accuracy. This thesis presents the proposition of a new vertex detector for the Belle II experiment, along with its software implementation. With Belle, this thesis presents a new time-dependent measurement of the CP violation with B^0→K_S^0 π^+ π^- γ, which can improve the constrains on some Standard Model parameters. With Belle II, the rediscovery of B^0→K_S^0 π^+ π^- γ and the branching fraction measurement of B^0→K_S^0 π^0 γ with around 190 fb-1 is described. The result of B(B^0→K_S^0 π^0 γ)=(7.28±1.75(stat)±1.03(syst))×〖10〗^(-6) is compatible with the predictions
A new Software Training Model at Belle II
No full textThe physics output of modern experimental HEP collaborations hinges not only on the quality of its software but also on the ability of the collaborators to make the best possible use of it. With the COVID-19 pandemic making in-person training impossible, the training paradigm at Belle II was shifted from periodic workshops towards guided self-study.To that end, the study material was rebuilt from scratch as a series of modular and hands-on lessons tightly integrated with the software documentation using Sphinx. Each lesson contains multiple exercises that are supplemented with hints and complete solutions. Rather than duplicating information, students are systematically taught to work with the technical reference documentation to find the important sections for themselves. Unit tests ensure that all examples work with different software versions, and feedback buttons make it easy to submit comments for improvements
A new Software Training Model at Belle II
No full textThe physics output of modern experimental HEP collaborations hinges not only on the quality of its software but also on the ability of the collaborators to make the best possible use of it. With the COVID-19 pandemic making in-person training impossible, the training paradigm at Belle II was shifted from periodic workshops towards guided self-study.To that end, the study material was rebuilt from scratch as a series of modular and hands-on lessons tightly integrated with the software documentation using Sphinx. Each lesson contains multiple exercises that are supplemented with hints and complete solutions. Rather than duplicating information, students are systematically taught to work with the technical reference documentation to find the important sections for themselves. Unit tests ensure that all examples work with different software versions, and feedback buttons make it easy to submit comments for improvements
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