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We report a search for a heavy neutral lepton (HNL) that mixes predominantly with . The search utilizes data collected with the Belle detector at the KEKB asymmetric energy collider. The data sample was collected at and just below the center-of-mass energies of the and resonances and has an integrated luminosity of , corresponding to events. We search for production of the HNL (denoted ) in the decay followed by its decay via . The search focuses on the parameter-space region in which the HNL is long-lived, so that the originate from a common vertex that is significantly displaced from the collision point of the KEKB beams. Consistent with the expected background yield, one event is observed in the data sample after application of all the event-selection criteria. We report limits on the mixing parameter of the HNL with the neutrino as a function of the HNL mass. Published by the American Physical Society2024
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A<sc>bstract</sc> We measure the cross section ofe+e−→ηcJ/ψat the Υ(nS)(n= 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of 955 fb−1. We also search for double charmonium production ine+e−→ηcJ/ψvia initial state radiation near theηcJ/ψthreshold. No evident signal of the double charmonium state is found, but evidence for thee+e−→ ηcJ/ψprocess is found with a statistical significance greater than 3.3σnear theηcJ/ψthreshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.more » « less
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A<sc>bstract</sc> We report the first measurement of the inclusivee+e−→$$ b\overline{b} $$ →$$ {D}_s^{\pm } $$ Xande+e−→$$ b\overline{b} $$ → D0/$$ {\overline{D}}^0 $$ Xcross sections in the energy range from 10.63 to 11.02 GeV. Based on these results, we determineσ(e+e−→$$ {B}_s^0{\overline{B}}_s^0 $$ X) andσ(e+e−→$$ B\overline{B} $$ X) in the same energy range. We measure the fraction of$$ {B}_s^0 $$ events at Υ(10860) to befs= ($$ {22.0}_{-2.1}^{+2.0} $$ )%. We determine also the ratio of the$$ {B}_s^0 $$ inclusive branching fractions$$ \mathcal{B} $$ ($$ {B}_s^0 $$ → D0/$$ {\overline{D}}^0 $$ X)/$$ \mathcal{B} $$ ($$ {B}_s^0 $$ →$$ {D}_s^{\pm } $$ X) = 0.416 ± 0.018 ± 0.092. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energye+e−collider.more » « less
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A<sc>bstract</sc> We present the analysis of two-particle angular correlations using coordinate systems defined with the conventional beam axis and the event thrust axis. We propose the latter as a good representation for the correlation structure interpretation in thee+e−collision system. Thee+e−collisions to hadronic final states at center-of-mass energies of$$ \sqrt{s} $$ = 10.52 GeV and 10.58 GeV are recorded by the Belle detector at KEKB. In this paper, results on the first dataset are supplementary to the previous Belle publication [1]. At the same time, the latter is the first two-particle correlation measurement at collision energy on theΥ(4S) resonance and is sensitive to its decay products. Measurements are reported as a function of the charged-particle multiplicity. Finally, a qualitative understanding of the correlation structure is discussed using a combination of Monte Carlo simulations and experimental data.more » « less
