14 research outputs found
Performance of the Belle II Silicon Vertex Detector
The Belle II experiment at the SuperKEKB collider of KEK (Japan) will accumulate 50 ab−1 of e+e− collision data at an unprecedented instantaneous luminosity of 8 ×1035 cm−2s−1, about 40 times larger than its predecessor. The Belle II vertex detector plays a crucial role in the rich Belle II physics program, especially for time-dependent measurements. It consists of two layers of DEPFET-based pixels and four layers of double sided silicon strips detectors(SVD). The vertex detector has been recently completed and installed in Belle II for the physics run started in spring 2019. We report here results on the commissioning of the SVD and its performance measured with the first collision data set
Measurement of the branching fractions for Cabibbo-suppressed decays and at Belle
International audienceWe present measurements of the branching fractions for the singly Cabibbo-suppressed decays and , and the doubly Cabibbo-suppressed decay , based on 980 of data recorded by the Belle experiment at the KEKB collider. We measure these modes relative to the Cabibbo-favored modes and . Our results for the ratios of branching fractions are , , and , where the uncertainties are statistical and systematic, respectively. The second value corresponds to , where 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 and yields , , and , 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
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
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
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 production ratio in collisions at the resonance using decays at Belle
We measure the ratio of branching fractions for the decays to and using and samples, where stands for ( or ), with fb of data collected at the resonance with the Belle detector. We find the decay rate ratio of over to be , which is the most precise measurement to date. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainty is systematic due to the assumption of isospin symmetry in
Alignment for the first precision measurements at Belle II
International audienceOn 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
Measurement of branching fractions of and at Belle
We present a study of a singly Cabibbo-suppressed decay and a Cabibbo-favored decay based on 980 of data collected by the Belle detector, operating at the KEKB energy-asymmetric collider. We measure their branching fractions relative to : and . Combining with the world average , we have the absolute branching fractions: and . The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the uncertainty on . The mode is observed for the first time and has a statistical significance of . The branching fraction of has been measured with a threefold improvement in precision over previous results and is found to be consistent with the world average