We present the first measurements of absolute branching fractions of Ξ_{c}^{0} decays into Ξ^{-}π^{+}, ΛK^{-}π^{+}, and pK^{-}K^{-}π^{+} final states. The measurements are made using a dataset ...comprising (772±11)×10^{6} BBover ¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. We first measure the absolute branching fraction for B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0} using a missing-mass technique; the result is B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})=(9.51±2.10±0.88)×10^{-4}. We subsequently measure the product branching fractions B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→Ξ^{-}π^{+}), B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→ΛK^{-}π^{+}), and B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→pK^{-}K^{-}π^{+}) with improved precision. Dividing these product branching fractions by the result for B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0} yields the following branching fractions: B(Ξ_{c}^{0}→Ξ^{-}π^{+})=(1.80±0.50±0.14)%, B(Ξ_{c}^{0}→ΛK^{-}π^{+})=(1.17±0.37±0.09)%, and B(Ξ_{c}^{0}→pK^{-}K^{-}π^{+})=(0.58±0.23±0.05)%. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for B(Ξ_{c}^{0}→Ξ^{-}π^{+}) can be combined with Ξ_{c}^{0} branching fractions measured relative to Ξ_{c}^{0}→Ξ^{-}π^{+} to yield other absolute Ξ_{c}^{0} branching fractions.
We present the first measurements of absolute branching fractions of Ξc0 decays into Ξ−π+, ΛK−π+, and pK−K−π+ final states. The measurements are made using a dataset comprising (772±11)×106 BB¯ pairs ...collected at the ϒ(4S) resonance with the Belle detector at the KEKB e+e− collider. We first measure the absolute branching fraction for B−→Λ¯c−Ξc0 using a missing-mass technique; the result is B(B−→Λ¯c−Ξc0)=(9.51±2.10±0.88)×10−4. We subsequently measure the product branching fractions B(B−→Λ¯c−Ξc0)B(Ξc0→Ξ−π+), B(B−→Λ¯c−Ξc0)B(Ξc0→ΛK−π+), and B(B−→Λ¯c−Ξc0)B(Ξc0→pK−K−π+) with improved precision. Dividing these product branching fractions by the result for B−→Λ¯c−Ξc0 yields the following branching fractions: B(Ξc0→Ξ−π+)=(1.80±0.50±0.14)%, B(Ξc0→ΛK−π+)=(1.17±0.37±0.09)%, and B(Ξc0→pK−K−π+)=(0.58±0.23±0.05)%. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for B(Ξc0→Ξ−π+) can be combined with Ξc0 branching fractions measured relative to Ξc0→Ξ−π+ to yield other absolute Ξc0 branching fractions.
We report the first observation of the double strange baryon Ξ(1620)^{0} in its decay to Ξ^{-}π^{+} via Ξ_{c}^{+}→Ξ^{-}π^{+}π^{+} decays based on a 980 fb^{-1} data sample collected with the Belle ...detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The mass and width are measured to be 1610.4±6.0(stat)_{-4.2}^{+6.1} (syst) MeV/c^{2} and 59.9±4.8(stat)_{-7.1}^{+2.8}(syst) MeV, respectively. We obtain 4.0σ evidence of the Ξ(1690)^{0} with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S=-2.
We report the first observation of the radiative decay of the ϒ(1S) into a charmonium state. The significance of the observed signal of ϒ(1S)→γχ_{c1} is 6.3 standard deviations including systematics. ...The branching fraction is calculated to be Bϒ(1S)→γχ_{c1}=4.7_{-1.8}^{+2.4}(stat)_{-0.5}^{+0.4}(sys)×10^{-5}. We also searched for ϒ(1S) radiative decays into χ_{c0,2} and η_{c}(1S,2S), and set upper limits on their branching fractions. These results are obtained from a 24.9 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider at a center-of-mass energy equal to the ϒ(2S) mass using ϒ(1S) tagging by the ϒ(2S)→ϒ(1S)π^{+}π^{-} transitions.
Run and slow control system of the Belle II silicon vertex detector Irmler, C.; Aihara, H.; Aziz, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2020, Letnik:
958
Journal Article
Recenzirano
Odprti dostop
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.
The lifetime of the τ lepton is measured using the process e+ e- → τ+ τ- , where both τ leptons decay to 3πν(τ). The result for the mean lifetime, based on 711 fb(-1) of data collected with the ...Belle detector at the ϒ(4S) resonance and 60 MeV below, is τ=(290.17±0.53(stat)±0.33(syst))×10(-15) s. The first measurement of the lifetime difference between τ+ and τ- is performed. The upper limit on the relative lifetime difference between positive and negative τ leptons is |Δτ|/τ<7.0×10(-3) at 90% C.L.
Observation of ϒ(4S)→η^{'}ϒ(1S) Al Said, S; Asner, D M; Ayad, R ...
Physical review letters,
2018-Aug-10, Letnik:
121, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We report the first observation of the hadronic transition ϒ(4S)→η^{'}ϒ(1S), using 496 fb^{-1} data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} ...collider. We reconstruct the η^{'} meson through its decays to ρ^{0}γ and to π^{+}π^{-}η, with η→γγ. We measure B(ϒ(4S)→η^{'}ϒ(1S))=3.43±0.88(stat)±0.21(syst)×10^{-5}, with a significance of 5.7σ.
Performance of the Belle II Silicon Vertex Detector Tanigawa, H.; Adamczyk, K.; Aihara, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2020, Letnik:
972
Journal Article
Recenzirano
Odprti dostop
The Belle II experiment at the SuperKEKB collider of KEK (Japan) started recording physics data in spring 2019 with all its subdetectors installed and with the goal of accumulating 50ab−1 of e+e− ...collision events at the unprecedented instantaneous luminosity of 8×1035cm−2s−1, about 40 times larger than its predecessor. The Belle II vertex detector plays a crucial role in the broad Belle II physics program, especially for time-dependent CP measurements. It consists of two layers of DEPFET-based pixels and four layers of double-sided silicon strip detectors (SVD).
The experience gained from the first period of SVD operation can be summarized as smooth and reliable running of the detector, with high stability of noise levels and calibration parameters obtained from local calibration runs. No major problem has been experienced. The detector even survived a few serious radiation accidents in which the beam was lost due to failure in the machine focusing quadrupoles without any notable damage. The SVD performance were carefully studied with these first physics data. The SVD showed excellent hit and tracking efficiency. Moreover, cluster energy and signal to noise ratio as well as the hit time and spatial resolutions measured on data showed a fair agreement with the expected performance.
•Belle II silicon vertex detector operated during the first year of the experiment.•All sensors worked with stable and excellent hit efficiencies above 99 %.•Signal-to-noise ratios between 15 and 30, cluster time resolution better than 3 ns.•First effects of irradiation visible in leakage currents.
This paper shows the hardware and the procedure utilized to test all components of the readout system (cables, FADC boards, junction boards) of the Belle II Silicon Vertex Detector after the series ...production. For the FADC board special testing hardware and firmware were designed and created to check all digital and analog inputs and outputs as well as all data interconnections on the board. The main FPGA on the FADC board generates digital signals which are converted to periodic analog differential alternating voltages up to 40 MHz on the FADC board tester, which then are fed into the analog inputs of the FADC board. Histograms and scans of the samples are recorded by using random equivalent-time sampling or sequential equivalent-time sampling, allowing to characterize the behavior of the system with a much higher bandwidth than the ADCs could do with conventional measurements. Small changes of parameters of the assembly (like using a cable of different length) lead to significant changes of the measured values, creating a sensitive testing instrument. The shapes of the distributions are analyzed and compared to references by software which then decides if a test is passed or not.
The commissioning setup of the whole readout chain, with all the final components including the final detector, has been tested in three phases. The respective graphs of the signal-to-noise ratios of the strips of a detector module and histograms of the noise development of the whole detector show very high consistency of the SVD readout system.
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