We search for lepton-number- and baryon-number-violating decays τ− → ¯pe+e−, pe−e−, ¯pe+μ−, ¯pe−μ+, ¯pμ+μ−, and pμ−μ− using 921 fb−1 of data, equivalent to (841 ± 12) × 106 τ+τ− 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) × 10−8. We set the world's first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels.
Using 980 fb−1 of data collected with the Belle detector operating at the KEKB asymmetric-energy e+e− collider, we report a study of the electromagnetic decays of excited charmed baryons Ξc(2790) and ...Ξc(2815). A clear signal (8.6 standard deviations) is observed for ... and we measure: ... We also present evidence (3.8 standard deviations) for the similar decay of the Ξc(2790)0 and measure: ... The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the Ξc(2815)+ and Ξc(2790)+ baryons and set upper limits at the 90% confidence level of: ..., and ... Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states. (ProQuest: ... denotes formula omitted.)
We measure the lifetime of the $D_s^+$ meson using a data sample of 207 fb$^{-1}$ collected by the Belle II experiment running at the SuperKEKB asymmetric-energy $e^+ e^-$ collider. The lifetime is ...determined by fitting the decay-time distribution of a sample of $116\times 10^3$ $D_s^+\rightarrow\phi\pi^+$ decays. Our result is $\tau^{}_{D^+_s} = (498.7\pm 1.7\,^{+1.1}_{-0.8})$ fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.
A
bstract
We present a search for the charged lepton-flavor-violating decays ϒ(1
S
)
→
ℓ
±
ℓ
′
∓
and radiative charged lepton-flavour-violating decays ϒ(1
S
)
→ γ
ℓ
±
ℓ
′
∓
ℓ
,
ℓ
′ =
e, μ, τ
using ...the 158 million ϒ(2
S
) sample collected by the Belle detector at the KEKB collider. This search uses ϒ(1
S
) mesons produced in ϒ(2
S
)
→ π
+
π
−
ϒ(1
S
) transitions. We do not find any significant signal, so we provide upper limits on the branching fractions at the 90% confidence level.
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