587 research outputs found
Search for Zā² āĪ¼+Ī¼- in the LĪ¼-LĻ gauge-symmetric model at Belle
We search for a new gauge boson Zā² that couples only to heavy leptons and their corresponding neutrinos in the process e+e-āZā²(āĪ¼+Ī¼-)Ī¼+Ī¼-, using a 643 fb-1 data sample collected by the Belle experiment at or near the Ļ(1S,2S,3S,4S,5S) resonances at the KEKB collider. While previous searches for Zā² performed a data-based estimation of the initial state radiation effect, our search for the Zā² is the first to include effects due to initial state radiation in the signal simulated samples that were used in estimating the detection efficiency. No signal is observed in the Zā² mass range of 0.212-10 GeV/c2, and we set an upper limit on the coupling strength, gā², constraining the possible Zā² contribution to the anomalous magnetic dipole moment of the muon
Search for the decay Bs0 āĪ·ā²Ī·
We report the results of the first search for the decay Bs0āĪ·ā²Ī· using 121.4 fb-1 of data collected at the I (5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e-collider. We observe no significant signal and set a 90% confidence-level upper limit of 6.5Ć10-5 on the branching fraction of this decay
Measurement of B (Bs ādsX) with Bs semileptonic tagging
We report the first direct measurement of the inclusive branching fraction B(BsāDsX) via Bs tagging in e+e-ā (5S) events. Tagging is accomplished through a partial reconstruction of semileptonic decays BsāDsXāĪ½, where X denotes unreconstructed additional hadrons or photons and ā is an electron or muon. With 121.4 fb-1 of data collected at the (5S) resonance by the Belle detector at the KEKB asymmetric-energy e+e- collider, we obtain B(BsāDsX)=(60.2Ā±5.8Ā±2.3)%, where the first uncertainty is statistical and the second is systematic
Measurement of branching fractions and search for CP violation in D \u3csup\u3e0\u3c/sup\u3e ā Ļ \u3csup\u3e+\u3c/sup\u3e Ļ \u3csup\u3e ā\u3c/sup\u3e Ī·, D \u3csup\u3e0\u3c/sup\u3e ā K \u3csup\u3e+\u3c/sup\u3e K \u3csup\u3e ā\u3c/sup\u3e Ī·, and D \u3csup\u3e0\u3c/sup\u3e ā ĻĪ· at Belle
We measure the branching fractions and CP asymmetries for the singly Cabibbo-suppressed decays D0 ā Ļ+ĻāĪ·, D0 ā K+KāĪ·, and D0 ā ĻĪ·, using 980 fbā1 of data from the Belle experiment at the KEKB e+eā collider. We obtainB(D0āĻ+ĻāĪ·)=[1.22Ā±0.02(stat)Ā±0.02(syst)Ā±0.03(Bref)]Ć10ā3,B(D0āK+KāĪ·)=[1.80ā0.06+0.07(stat)Ā±0.04(syst)Ā±0.05(Bref)]Ć10ā4,B(D0āĻĪ·)=[1.84Ā±0.09(stat)Ā±0.06(syst)Ā±0.05(Bref)]Ć10ā4, where the third uncertainty (Bref) is from the uncertainty in the branching fraction of the reference mode D0 ā KāĻ+Ī·. The color-suppressed decay D0 ā ĻĪ· is observed for the first time, with very high significance. The results for the CP asymmetries areACP(D0Ļ+ĻāĪ·)=[0.9Ā±1.2(stat)Ā±0.5(syst)]%,ACP(D0āK+KāĪ·)=[ā1.4Ā±3.3(stat)Ā±1.1(syst)]%,ACP(D0āĻĪ·)=[ā1.9Ā±4.4(stat)Ā±0.6(syst)]%. The results for D0 ā Ļ+ĻāĪ· are a significant improvement over previous results. The branching fraction and ACP results for D0 ā K+KāĪ·, and the ACP result for D0 ā ĻĪ·, are the first such measurements. No evidence for CP violation is found in any of these decays. [Figure not available: see fulltext.
The Belle II SVD detector
The Silicon Vertex Detector (SVD) is one of the main detectors in the Belle II experiment at KEK, Japan. In combination with a pixel detector, the SVD determines precise decay vertex and low-momentum track reconstruction. The SVD ladders are being developed at several institutes. For the development of the tracking algorithm as well as the performance estimation of the ladders, beam tests for the ladders were performed. We report an overview of the SVD development, its performance measured in the beam test, and the prospect of its assembly and commissioning until installation
Search for the dark photon in B \u3csup\u3e0\u3c/sup\u3e ā Aā²Aā², Aā² ā e \u3csup\u3e+\u3c/sup\u3e e \u3csup\u3e ā\u3c/sup\u3e, Ī¼ \u3csup\u3e+\u3c/sup\u3e Ī¼ \u3csup\u3e ā\u3c/sup\u3e, and Ļ \u3csup\u3e+\u3c/sup\u3e Ļ \u3csup\u3e ā\u3c/sup\u3e decays at Belle
We present a search for the dark photon Aā² in the B0 ā Aā²Aā² decays, where Aā² subsequently decays to e+eā, Ī¼+Ī¼ā, and Ļ+Ļā. The search is performed by analyzing 772 Ć 106BBĀÆ events collected by the Belle detector at the KEKB e+eā energy-asymmetric collider at the Ļ(4S) resonance. No signal is found in the dark photon mass range 0.01 GeV/c2 ā¤ mAā² ā¤ 2.62 GeV/c2, and we set upper limits of the branching fraction of B0 ā Aā²Aā² at the 90% confidence level. The products of branching fractions, ā¬(B0āAā²Aā²)Ćā¬(Aā²āe+eā)2 and ā¬(B0āAā²Aā²)Ćā¬(Aā²āĪ¼+Ī¼ā)2, have limits of the order of 10ā8 depending on the Aā² mass. Furthermore, considering Aā² decay rate to each pair of charged particles, the upper limits of ā¬ (Bā Aā² Aā²) are of the order of 10ā8ā10ā5. From the upper limits of ā¬ (Bā Aā² Aā²) , we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10ā2ā10ā1 at mhā²āmB0 Ā± 40 MeV/c2 and 10ā1ā1 at mhā²āmB0 Ā± 3 GeV/c2. [Figure not available: see fulltext.
Performance studies of the Belle II Silicon Vertex Detector with data taken at the DESY test beam in April 2016
Belle II is a multipurpose detector currently under construction which will be operated at the next generation B-factory SuberKEKB in Japan. Its main devices for the vertex reconstruction are the Silicon Vertex Detector (SVD) and the Pixel Detector (PXD). In April 2016 a sector of the Belle II SVD and PXD have been tested in a beam of high energetic electrons at the test beam facility at DESY Hamburg (Germany). We report here the results for the hit efficiency estimation and the measurement of the resolution for the Belle II silicon vertex etector. We find that the hit efficiencies are on average above 99.5% and that the measured resolution is within the expectations
Performance studies of the Belle II Silicon Vertex Detector with data taken at the DESY test beam in April 2016
Belle II is a multipurpose detector currently under construction which will be operated at the next generation B-factory SuberKEKB in Japan. Its main devices for the vertex reconstruction are the Silicon Vertex Detector (SVD) and the Pixel Detector (PXD). In April 2016 a sector of the Belle II SVD and PXD have been tested in a beam of high energetic electrons at the test beam facility at DESY Hamburg (Germany). We report here the results for the hit efficiency estimation and the measurement of the resolution for the Belle II silicon vertex etector. We find that the hit efficiencies are on average above 99.5% and that the measured resolution is within the expectations
Measurement of the Branching Fraction of the Decay in Fully Reconstructed Events at Belle
We present an analysis of the exclusive
decay, where represents an
electron or a muon, with the assumption of charge-conjugation symmetry and
lepton universality. The analysis uses the full data sample
collected by the Belle detector, corresponding to 711 fb of integrated
luminosity. We select the events by fully reconstructing one meson in
hadronic decay modes, subsequently determining the properties of the other
meson. We extract the signal yields using a binned maximum-likelihood fit to
the missing-mass squared distribution in bins of the invariant mass of the two
pions or the momentum transfer squared. We measure a total branching fraction
of , where the
uncertainties are statistical and systematic, respectively. This result is the
first reported measurement of this decay.Comment: 23 pages, 19 figure
Search for lepton-number- And baryon-number-violating tau decays at Belle
Ā© 2020 authors. Published by the American Physical Society. We search for lepton-number- and baryon-number-violating decays Ļ-āpĀÆe+e-, pe-e-, pĀÆe+Ī¼-, pĀÆe-Ī¼+, pĀÆĪ¼+Ī¼-, and pĪ¼-Ī¼- using 921 fb-1 of data, equivalent to (841Ā±12)Ć106 Ļ+Ļ- events, recorded with the Belle detector at the KEKB asymmetric-energy e+e- collider. In the absence of a signal, 90% confidence-level upper limits are set on the branching fractions of these decays in the range (1.8-4.0)Ć10-8. We set the world\u27s first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels
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