We report results from a study of $B^\pm \rightarrow DK^\pm$ decays followed
by $D$ decaying to $CP$~eigenstates, where $D$ indicates a $D^0$ or
$\bar{D}^{0}$ meson. These decays are sensitive to the
...Cabibbo-Kobayashi-Maskawa unitarity-triangle angle $\phi_{3}$. The results are
based on a combined analysis of the final data set of $772 \times
10^6~B\bar{B}$ pairs collected by the Belle experiment and a data set of $198
\times 10^6~B\bar{B}$ pairs collected by the Belle~II experiment, both in
electron-positron collisions at the $\Upsilon(4S)$ resonance. We measure the
$CP$ asymmetries to be $\mathcal{ A}_{CP +} =~(+12.5 \pm 5.8 \pm 1.4)\% $ and
$\mathcal{ A}_{CP -} =~(-16.7 \pm 5.7 \pm 0.6)\%$, and the ratios of branching
fractions to be $\mathcal{ R}_{CP+}=~1.164 \pm 0.081 \pm 0.036 $ and $\mathcal{
R}_{CP-} =~1.151 \pm 0.074 \pm 0.019$. The first contribution to the
uncertainties is statistical, and the second is systematic. The asymmetries
$\mathcal{A}_{CP +}$ and $\mathcal{A}_{CP -}$ have similar magnitudes and
opposite signs; their difference corresponds to 3.5~standard deviations. From
these values we calculate 68.3\% confidence intervals of
($8.5^{\circ}<\phi_{3}<16.5^{\circ}$) or ($84.5^{\circ}<\phi_{3}<95.5^{\circ}$)
or ($163.3^{\circ}<\phi_{3}<171.5^{\circ}$) and $0.321<r_{B}<0.465$.
Phys. Rev. D 108, 072012 (2023) We present a measurement of time-dependent rate asymmetries in $B^0\to \phi
K^0_S$ decays to search for non-standard-model physics in $b\to q
\overline{q}s$ ...transitions. The data sample is collected with the Belle II
detector at the SuperKEKB asymmetric-energy $e^{+}e^{-}$ collider in 2019-2022
and contains $(387\pm 6)\times 10^6$ bottom-antibottom mesons from
$\Upsilon(4S)$ resonance decays. We reconstruct $162\pm17$ signal events and
extract the charge-parity ($CP$) violating parameters from a fit to the
distribution of the proper-decay-time difference of the two $B$ mesons. The
measured direct and mixing-induced $CP$ asymmetries are $A=0.31\pm0.20\pm0.05$
and $S=0.54\pm0.26^{+0.06}_{-0.08}$, respectively, where the first
uncertainties are statistical and the second are systematic. The results are
compatible with the $CP$ asymmetries observed in $b\to c\overline{c} s$
transitions.
Phys. Rev. Lett. 131, 121802 (2023) We report the first search for a non-standard-model resonance decaying into
$\tau$ pairs in $e^{+}e^{-}\rightarrow \mu^{+}\mu^{-} \tau^+\tau^-$ events in
the ...3.6-10 GeV/$c^{2}$ mass range. We use a 62.8 fb$^{-1}$ sample of $e^+e^-$
collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II
experiment at the SuperKEKB collider. The analysis probes three different
models predicting a spin-1 particle coupling only to the heavier lepton
families, a Higgs-like spin-0 particle that couples preferentially to charged
leptons (leptophilic scalar), and an axion-like particle, respectively. We
observe no evidence for a signal and set exclusion limits at 90% confidence
level on the product of cross section and branching fraction into $\tau$ pairs,
ranging from 0.7 fb to 24 fb, and on the couplings of these processes. We
obtain world-leading constraints on the couplings for the leptophilic scalar
model for masses above 6.5 GeV/$c^2$ and for the axion-like particle model over
the entire mass range.
Additional spin-0 particles appear in many extensions of the standard model.
We search for long-lived spin-0 particles $S$ in $B$-meson decays mediated by a
$b\to s$ quark transition in $e^+e^-$ ...collisions at the $\Upsilon(4S)$
resonance at the Belle II experiment. Based on a sample corresponding to an
integrated luminosity of $189 \mathrm{\,fb}^{-1}$, we observe no evidence for
signal. We set model-independent upper limits on the product of branching
fractions $\mathrm{Br}(B^0\to K^*(892)^0(\to K^+\pi^-)S)\times \mathrm{Br}(S\to
x^+x^-)$ and $\mathrm{Br}(B^+\to K^+S)\times \mathrm{Br}(S\to x^+x^-)$, where
$x^+x^-$ indicates $e^+e^-, \mu^+\mu^-, \pi^+\pi^-$, or $K^+K^-$, as functions
of $S$ mass and lifetime at the level of $10^{-7}$.
Journal of High Energy Physics 09(2023)146 We measure $C\!P$ asymmetries and branching-fraction ratios for $B^\pm \to
DK^\pm$ and $D\pi^\pm$ decays with $D\to K^0_{\rm S} K^\pm\pi^\mp$, where $D$
is ...a superposition of $D^0$ and $\bar{D}^0$. We use the full data set of the
Belle experiment, containing $772\times 10^6~B\bar{B}$ pairs, and data from the
Belle~II experiment, containing $387\times 10^6~B\bar{B}$ pairs, both collected
in electron-positron collisions at the $\Upsilon(4S)$ resonance. Our results
provide model-independent information on the unitarity triangle angle $\phi_3$.
We present a measurement of the $\tau$-lepton mass using a sample of about
175 million $e^+e^- \to \tau^+\tau^-$ events collected with the Belle II
detector at the SuperKEKB $e^+e^-$ collider at a ...center-of-mass energy of
$10.579\,\mathrm{Ge\kern -0.1em V}$. This sample corresponds to an integrated
luminosity of $190\,\mathrm{fb^{-1}}$. We use the kinematic edge of the $\tau $
pseudomass distribution in the decay ${\tau^-\to\pi^-\pi^+\pi^-\nu_\tau}$ and
measure the $\tau$ mass to be $1777.09 \pm 0.08 \pm 0.11 \,\mathrm{Me\kern
-0.1em V\!/c^2}$, where the first uncertainty is statistical and the second
systematic. This result is the most precise to date.
PRL 131, 111803 (2023) We report a measurement of the $C\!P$-violating parameters $A$ and $S$ in
$B^{0}\to K_{S}^{0} \pi^{0}$ decays at Belle II using a sample of $387\times
10^{6}$ $B\bar{B}$ events ...recorded in $e^{+}e^{-}$ collisions at a
center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. These
parameters are determined by fitting the proper decay-time distribution of a
sample of 415 signal events. We obtain $A = 0.04^{+0.15}_{-0.14}\pm 0.05$ and
$S = 0.75^{+0.20}_{-0.23}\pm 0.04$, where the first uncertainties are
statistical and the second are systematic.
We report measurements of the branching fraction and $\it CP$ asymmetry in
$B^{0} \to \pi^{0} \pi^{0}$ decays reconstructed at Belle II in an
electron-positron collision sample containing $198 \times ...10^{6}$
$B\overline{B}$ pairs. We measure a branching fraction $\mathcal{B}(\Bpipi) =
(1.38 \pm 0.27 \pm 0.22) \times 10^{-6}$ and a $\it CP$ asymmetry $\Acp(\Bpipi)
= 0.14 \pm 0.46 \pm 0.07$, where the first uncertainty is statistical and the
second is systematic.
We measure the $B^0$ lifetime and flavor-oscillation frequency using $B^0\to
D^{(*)-}\pi^+$ decays collected by the Belle II experiment in asymmetric-energy
$e^+e^-$ collisions produced by the ...SuperKEKB collider operating at the
$\Upsilon(4S)$ resonance. We fit the decay-time distribution of signal decays,
where the initial flavor is determined by identifying the flavor of the other
$B$ meson in the event. The results, based on $33000$ signal decays
reconstructed in a data sample corresponding to ${190}\text{fb}^{-1}$, are
$\tau_{B^0} = {1.499}\pm{0.013}\pm{0.008}\;\text{ps}$, $\Delta m_d =
{0.516}\pm{0.008}\pm{0.005}\;\text{ps}^{-1}$, where the first uncertainties are
statistical and the second are systematic. These results are consistent with
the world-average values.
We report a measurement of the mixing-induced and direct $\textit{CP}$
violation parameters $S_{\text{CP}}$ and $A_{\text{CP}}$ from $B^0 \to J/\psi
K^0_S$ decays reconstructed by the Belle II ...experiment at the SuperKEKB
asymmetric-energy electron-positron collider. The data, collected at the
center-of-mass energy of the $\Upsilon(4S)$ resonance, correspond to
$190\text{fb}^{-1}$ of integrated luminosity. We measure ${S_{\text{CP}} =
0.720\pm0.062\pm0.016}$ and $A_{\text{CP}} = 0.094\pm0.044^{+0.042}_{-0.017}$,
where the first uncertainties are statistical and the second systematic. In the
Standard Model, $S_{\text{CP}}$ equals $\sin(2\phi_1)$ to a good approximation.
