We report a measurement of decay-time dependent $CP$-violating parameters in
$B^0 \rightarrow K^0_S K^0_S K^0_S$ decays. We use $(198.0 \pm 3.0) \times
10^6\ B\overline{B}$ pairs collected at the ...$\Upsilon(4S)$ resonance with the
Belle II detector at the SuperKEKB asymmetric-energy $e^+e^-$ collider. The
observed mixing-induced and direct $CP$ violation parameters are $\mathcal{S} =
-1.86\ _{-0.46}^{+0.91}~{\rm (stat)} \pm 0.09~{\rm (syst)}$ and $\mathcal{A} =
-0.22\ _{-0.27}^{+0.30}~{\rm (stat)} \pm 0.04~{\rm (syst)}$, respectively.
We present a measurement of the branching fraction and longitudinal
polarization of $B^0 \to \rho^+ \rho^-$ decays. SuperKEKB electron-positron
collision data corresponding to 189~fb$^{-1}$ of ...integrated luminosity and
containing $198 \times 10^6 B\bar{B}$ pairs collected with the Belle II
detector are used. We obtain \begin{eqnarray*}
\mathcal{B}(B^0\to\rho^+\rho^-) &=&
2.67\pm0.28\,(\mathrm{stat})\,\pm0.28\,(\mathrm{syst}) \times 10^{-5},
\end{eqnarray*} \begin{eqnarray*}
f_L &=& 0.956\pm0.035\,(\mathrm{stat})\,\pm 0.033\,(\mathrm{syst}),
\end{eqnarray*} These results are consistent with previous measurements and can
be used to constrain penguin pollution and to extract the quark-mixing angle
$\phi_2$.
We present a search for the lepton-flavour-violating decays $B^+ \to K^+
\tau^\pm \ell^\mp$, with $\ell = (e, \mu)$, using the full data sample of $772
\times 10^6$ $B\overline{B}$ pairs recorded by ...the Belle detector at the KEKB
asymmetric-energy $e^+ e^-$ collider. We use events in which one $B$ meson is
fully reconstructed in a hadronic decay mode. We find no evidence for $B^\pm
\to K^\pm \tau \ell$ decays and set upper limits on their branching fractions
at the 90% confidence level in the $(1$-$3) \times 10^{-5}$ range. The obtained
limits are the world's best results.
We determine the branching fractions ${\mathcal{B}}$ and $CP$ asymmetries
${\mathcal{A}_{{\it CP}}}$ of the decays $B^+ \rightarrow \pi^+ \pi^0$ and $B^+
\rightarrow K^+ \pi^0$. The results are based ...on a data set containing 198
million bottom-antibottom meson pairs corresponding to an integrated luminosity
of $190\;\text{fb}^{-1}$ recorded by the Belle II detector in energy-asymmetric
electron-positron collisions at the $\Upsilon (4S)$ resonance. We measure
${\mathcal{B}(B^+ \rightarrow \pi^+ \pi^0) = (6.12 \pm 0.53 \pm 0.53)\times
10^{-6}}$, ${\mathcal{B}(B^+ \rightarrow K^+ \pi^0) = (14.30 \pm 0.69 \pm
0.79)\times 10^{-6}}$, ${\mathcal{A}_{{\it CP}}(B^+ \rightarrow \pi^+ \pi^0) =
-0.085 \pm 0.085 \pm 0.019}$, and ${\mathcal{A}_{{\it CP}}(B^+ \rightarrow K^+
\pi^0) = 0.014 \pm 0.047 \pm 0.010}$, where the first uncertainties are
statistical and the second are systematic. These results improve a previous
Belle II measurement and agree with the world averages.
We present results on the semileptonic decays $B^0 \to \rho^- \ell^+
\nu_\ell$ and $B^+ \to \rho^0 \ell^+ \nu_\ell$ in a sample corresponding to
189.9/fb of Belle II data at the SuperKEKB $e^- e^+$ ...collider. Signal decays
are identified using full reconstruction of the recoil $B$ meson in hadronic
final states. We determine the total branching fractions via fits to the
distributions of the square of the "missing" mass in the event and the dipion
mass in the signal candidate and find ${\mathcal{B}(B^0\to\rho^-\ell^+
\nu_\ell) = (4.12 \pm 0.64(\mathrm{stat}) \pm 1.16(\mathrm{syst})) \times
10^{-4}}$ and ${\mathcal{B}({B^+\to\rho^0\ell^+\nu_\ell}) = (1.77 \pm 0.23
(\mathrm{stat}) \pm 0.36 (\mathrm{syst})) \times 10^{-4}}$ where the dominant
systematic uncertainty comes from modeling the nonresonant $B\to
(\pi\pi)\ell^+\nu_\ell$ contribution.
We measure the branching fraction of B- → τ- ν(τ) using the full Υ(4S) data sample containing 772×10(6) BB pairs collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. Events ...with BB pairs are tagged by reconstructing one of the B mesons decaying into hadronic final states, and B- → τ- ν(τ) candidates are detected in the recoil. We find evidence for B- → τ- ν(τ) with a significance of 3.0 standard deviations including systematic errors and measure a branching fraction B(B- → τ- ν(τ))=0.72(-0.25)(+0.27)(stat)±0.11(syst)×10(-4).
Phys. Rev. Lett. 130, 181804 (2023) We study $B^{+}\to \pi^{+}\pi^{0}\pi^{0}$ using 711 $\rm{fb}^{-1}$ of data
collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB
...asymmetric-energy $e^{+}e^{-}$ collider. We measure an inclusive branching
fraction of $(19.0\pm 1.5\pm 1.4)\times 10^{-6}$ and an inclusive \textit{CP}
asymmetry of $(9.2 \pm 6.8 \pm 0.7)\%$, where the first uncertainties are
statistical and the second are systematic; and a $B^{+}\to
\rho(770)^{+}\pi^{0}$ branching fraction of $(11.2\pm 1.1\pm 0.9
^{+0.8}_{-1.6})\times 10^{-6}$, where the third uncertainty is due to possible
interference with $B^{+}\to \rho(1450)^{+}\pi^{0}$. We present the first
observation of a structure around 1 GeV/$c^{2}$ in the $\pi^{0}\pi^{0}$ mass
spectrum, with a significance of 6.4$\sigma$, and measure a branching fraction
to be $(6.9\pm 0.9\pm 0.6)\times 10^{-6}$. We also report a measurement of
local \textit{CP} asymmetry in this structure.
Phys. Rev. Lett. 131, 051804 (2023) We present the first measurement of the ratio of branching fractions of
inclusive semileptonic $B$-meson decays, $R(X_{e/\mu}) = \mathcal{B}(B\to X \,
e \, \nu) / ...\mathcal{B}(B\to X \, \mu \, \nu)$, a precision test of
electron-muon universality, using data corresponding to $189\,\mathrm{fb}^{-1}$
from electron-positron collisions collected with the Belle II detector. In
events where the partner $B$ meson is fully reconstructed, we use fits to the
lepton momentum spectra above $1.3\,\mathrm{GeV}/c$ to obtain $R(X_{e/\mu}) =
1.007 \pm 0.009~(\mathrm{stat}) \pm 0.019~(\mathrm{syst})$, which is the most
precise lepton-universality test of its kind and agrees with the standard-model
expectation.
We observe evidence for CP violation in the decay D+ → K(S)(0)π+ using a data sample with an integrated luminosity of 977 fb(-1) collected by the Belle detector at the KEKB e+ e- asymmetric-energy ...collider. The CP asymmetry in the decay is measured to be (-0.363±0.094±0.067)%, which is 3.2 standard deviations away from zero, and is consistent with the expected CP violation due to the neutral kaon in the final state.
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