We study the processes e^{+}e^{-}→ωχ_{bJ}(1P) (J=0, 1, or 2) using samples at center-of-mass energies sqrts=10.701, 10.745, and 10.805 GeV, corresponding to 1.6, 9.8, and 4.7 fb^{-1} of integrated ...luminosity, respectively. These data were collected with the Belle II detector during special operations of the SuperKEKB collider above the ϒ(4S) resonance. We report the first observation of ωχ_{bJ}(1P) signals at sqrts=10.745 GeV. By combining Belle II data with Belle results at sqrts=10.867 GeV, we find energy dependencies of the Born cross sections for e^{+}e^{-}→ωχ_{b1,b2}(1P) to be consistent with the shape of the ϒ(10753) state. These data indicate that the internal structures of the ϒ(10753) and ϒ(10860) states may differ. Including data at sqrts=10.653 GeV, we also search for the bottomonium equivalent of the X(3872) state decaying into ωϒ(1S). No significant signal is observed for masses between 10.45 and 10.65 GeV/c^{2}.
Measurement of the Λ_{c}^{+} Lifetime Ahmed, H; Ahn, J K; Aloisio, A ...
Physical review letters,
2023-Feb-17, 20230217, Letnik:
130, Številka:
7
Journal Article
Recenzirano
An absolute measurement of the Λ_{c}^{+} lifetime is reported using Λ_{c}^{+}→pK^{-}π^{+} decays in events reconstructed from data collected by the Belle II experiment at the SuperKEKB ...asymmetric-energy electron-positron collider. The total integrated luminosity of the data sample, which was collected at center-of-mass energies at or near the ϒ(4S) resonance, is 207.2 fb^{-1}. The result, τ(Λ_{c}^{+})=203.20±0.89±0.77 fs, where the first uncertainty is statistical and the second systematic, is the most precise measurement to date and is consistent with previous determinations.
We present measurements of the branching fractions of eight $\overline
B{}^0\to D^{(*)+} K^- K^{(*)0}_{(S)}$, $B^{-}\to D^{(*)0} K^- K^{(*)0}_{(S)}$
decay channels. The results are based on data from ...SuperKEKB electron-positron
collisions at the $\Upsilon(4S)$ resonance collected with the Belle II
detector, corresponding to an integrated luminosity of $362~\text{fb}^{-1}$.
The event yields are extracted from fits to the distributions of the difference
between expected and observed $B$ meson energy, and are efficiency-corrected as
a function of $m(K^-K^{(*)0}_{(S)})$ and $m(D^{(*)}K^{(*)0}_{(S)})$ in order to
avoid dependence on the decay model. These results include the first
observation of $\overline B{}^0\to D^+K^-K_S^0$, $B^-\to D^{*0}K^-K_S^0$, and
$\overline B{}^0\to D^{*+}K^-K_S^0$ decays and a significant improvement in the
precision of the other channels compared to previous measurements. The
helicity-angle distributions and the invariant mass distributions of the $K^-
K^{(*)0}_{(S)}$ systems are compatible with quasi-two-body decays via a
resonant transition with spin-parity $J^P=1^-$ for the $K^-K_S^0$ systems and
$J^P= 1^+$ for the $K^-K^{*0}$ systems. We also present measurements of the
branching fractions of four $\overline B{}^0\to D^{(*)+} D_s^-$, $B^{-}\to
D^{(*)0} D_s^- $ decay channels with a precision compatible to the current
world averages.
We present a study of $\Xi_{c}^{0}\to\Xi^{0}\pi^{0}$,
$\Xi_{c}^{0}\to\Xi^{0}\eta$, and $\Xi_{c}^{0}\to\Xi^{0}\eta^{\prime}$ decays
using the Belle and Belle~II data samples, which have integrated ...luminosities
of 980~$\mathrm{fb}^{-1}$ and 426~$\mathrm{fb}^{-1}$, respectively. We measure
the following relative branching fractions $${\cal
B}(\Xi_{c}^{0}\to\Xi^{0}\pi^{0})/{\cal B}(\Xi_{c}^{0}\to\Xi^{-}\pi^{+}) = 0.48
\pm 0.02 ({\rm stat}) \pm 0.03 ({\rm syst}) ,$$ $${\cal
B}(\Xi_{c}^{0}\to\Xi^{0}\eta)/{\cal B}(\Xi_{c}^{0}\to\Xi^{-}\pi^{+}) = 0.11 \pm
0.01 ({\rm stat}) \pm 0.01 ({\rm syst}) ,$$ $${\cal
B}(\Xi_{c}^{0}\to\Xi^{0}\eta^{\prime})/{\cal B}(\Xi_{c}^{0}\to\Xi^{-}\pi^{+}) =
0.08 \pm 0.02 ({\rm stat}) \pm 0.01 ({\rm syst}) $$ for the first time, where
the uncertainties are statistical ($\rm stat$) and systematic ($\rm syst$). By
multiplying by the branching fraction of the normalization mode, ${\mathcal
B}(\Xi_{c}^{0}\to\Xi^{-}\pi^{+})$, we obtain the following absolute branching
fraction results $(6.9 \pm 0.3 ({\rm stat}) \pm 0.5 ({\rm syst}) \pm 1.3 ({\rm
norm})) \times 10^{-3}$, $(1.6 \pm 0.2 ({\rm stat}) \pm 0.2 ({\rm syst}) \pm
0.3 ({\rm norm})) \times 10^{-3}$, and $(1.2 \pm 0.3 ({\rm stat}) \pm 0.1 ({\rm
syst}) \pm 0.2 ({\rm norm})) \times 10^{-3}$, for $\Xi_{c}^{0}$ decays to
$\Xi^{0}\pi^{0}$, $\Xi^{0}\eta$, and $\Xi^{0}\eta^{\prime}$ final states,
respectively. The third errors are from the uncertainty on ${\mathcal
B}(\Xi_{c}^{0}\to\Xi^{-}\pi^{+})$. The asymmetry parameter for
$\Xi_{c}^{0}\to\Xi^{0}\pi^{0}$ is measured to be
$\alpha(\Xi_{c}^{0}\to\Xi^{0}\pi^{0}) = -0.90\pm0.15({\rm stat})\pm0.23({\rm
syst})$.
We report the result of a search for the rare decay $B^{0} \to \gamma \gamma$
using a combined dataset of $753\times10^{6}$ $B\bar{B}$ pairs collected by the
Belle experiment and $387\times10^{6}$ ...$B\bar{B}$ pairs collected by the Belle
II experiment from decays of the $\rm \Upsilon(4S)$ resonance produced in
$e^{+}e^{-}$ collisions. A simultaneous fit to the Belle and Belle II data sets
yields $11.0^{+6.5}_{-5.5}$ signal events, corresponding to a 2.5$\sigma$
significance. We determine the branching fraction $\mathcal{B}(B^{0} \to
\gamma\gamma) = (3.7^{+2.2}_{-1.8}(\rm stat)\pm0.5(\rm syst))\times10^{-8}$ and
set a 90% credibility level upper limit of $\mathcal{B}(B^{0} \to \gamma\gamma)
< 6.4\times10^{-8}$.
We report measurements of the $e^+e^- \to B\bar{B}$, $B\bar{B}{}^*$, and
$B^*\bar{B}{}^*$ cross sections at four energies, 10653, 10701, 10746 and 10805
MeV, using data collected by the Belle~II ...experiment. We reconstruct one $B$
meson in a large number of hadronic final states and use its momentum to
identify the production process. In the first $2-5$ MeV above $B^*\bar{B}{}^*$
threshold, the $e^+e^- \to B^*\bar{B}{}^*$ cross section increases rapidly.
This may indicate the presence of a pole close to the threshold.
We present a measurement of the ratio $R_\mu = \mathcal{B}(\tau^-\to
\mu^-\bar\nu_\mu\nu_\tau) / \mathcal{B}(\tau^-\to e^-\bar\nu_e\nu_\tau)$ of
branching fractions $\mathcal{B}$ of the $\tau$ lepton ...decaying to muons or
electrons using data collected with the Belle II detector at the SuperKEKB
$e^+e^-$ collider. The sample has an integrated luminosity of 362 fb$^{-1}$ at
a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a
binned maximum likelihood fit is performed using the momentum spectra of the
electron and muon candidates. The result, $R_\mu = 0.9675 \pm 0.0007 \pm
0.0036$, where the first uncertainty is statistical and the second is
systematic, is the most precise to date. It provides a stringent test of the
light-lepton universality, translating to a ratio of the couplings of the muon
and electron to the $W$ boson in $\tau$ decays of $0.9974 \pm 0.0019$, in
agreement with the standard model expectation of unity.
We present the result of a search for the charged-lepton-flavor violating
decay $\tau^- \to \mu^-\mu^+\mu^-$ using a $424fb^{-1}$ sample of data recorded
by the Belle II experiment at the SuperKEKB ...$e^{-}e^{+}$ collider. The
selection of $e^{-}e^{+}\to\tau^+\tau^-$ events is based on an inclusive
reconstruction of the non-signal tau decay, and on a boosted decision tree to
suppress background. We observe one signal candidate, which is compatible with
the expectation from background processes. We set a $90\%$ confidence level
upper limit of $1.9 \times 10^{-8}$ on the branching fraction of the \taumu
decay, which is the most stringent bound to date.
We report a determination of the CKM angle $\phi_{3}$, also known as
$\gamma$, from a combination of measurements using samples of up to
711~fb$^{-1}$ from the Belle experiment and up to ...362~fb$^{-1}$ from the Belle
II experiment. We combine results from analyses of $B^+\to DK^+, B^+\to
D\pi^+$, and $B^+ \to D^{*}K^+$ decays, where $D$ is an admixture of $D^0$ and
$\overline{D}{}^{0}$ mesons, in a likelihood fit to obtain $\phi_{3} =
(78.6^{+7.2}_{-7.3})^{\circ}$. We also briefly discuss the interpretation of
this result.
PRD 109, 111103 (2024) We measure the branching fraction of the decay $B^- \to D^0 \rho(770)^-$
using data collected with the Belle II detector. The data contain 387 million
$B\overline{B}$ pairs ...produced in $e^+e^-$ collisions at the $\Upsilon(4S)$
resonance. We reconstruct $8360\pm 180$ decays from an analysis of the
distributions of the $B^-$ energy and the $\rho(770)^-$ helicity angle. We
determine the branching fraction to be $(0.939 \pm 0.021\mathrm{(stat)} \pm
0.050\mathrm{(syst)})\%$, in agreement with previous results. Our measurement
improves the relative precision of the world average by more than a factor of
two.
