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 116×10^{3} D_{s}^{+}→ϕπ^{+} decays. Our result is τ_{D_{s}^{+}}=(499.5±1.7±0.9) fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.
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 a search for the baryon number $B$ and lepton number $L$ violating
decays $\tau^- \rightarrow \Lambda \pi^-$ and $\tau^- \rightarrow \bar{\Lambda}
\pi^-$ produced from the $e^+e^-\to ...\tau^+\tau^-$ process, using a 364
fb$^{-1}$ data sample collected by the Belle~II experiment at the SuperKEKB
collider. No evidence of signal is found in either decay mode, which have
$|\Delta(B-L)|$ equal to $2$ and $0$, respectively. Upper limits at 90\%
credibility level on the branching fractions of $\tau^- \rightarrow
\Lambda\pi^-$ and $\tau^- \rightarrow \bar{\Lambda}\pi^-$ are determined to be
$4.7 \times 10^{-8}$ and $4.3 \times 10^{-8}$, respectively.
We describe the planned near-term and potential longer-term upgrades of the Belle II detector at the SuperKEKB electron-positron collider operating at the KEK laboratory in Tsukuba, Japan. These ...upgrades will allow increasingly sensitive searches for possible new physics beyond the Standard Model in flavor, tau, electroweak and dark sector physics that are both complementary to and competitive with the LHC and other experiments.
We report a measurement of the $e^+e^- \to \pi^+\pi^-\pi^0$ cross section in
the energy range from 0.62 to 3.50 GeV using an initial-state radiation
technique. We use an $e^+e^-$ data sample ...corresponding to 191 $\text{fb}^{-1}$
of integrated luminosity, collected at a center-of-mass energy at or near the
$\Upsilon{(4S)}$ resonance with the Belle II detector at the SuperKEKB
collider. Signal yields are extracted by fitting the two-photon mass
distribution in $e^+e^- \to \pi^+\pi^-\pi^0\gamma$ events, which involve a
$\pi^0 \to \gamma\gamma$ decay and an energetic photon radiated from the
initial state. Signal efficiency corrections with an accuracy of 1.6% are
obtained from several control data samples. The uncertainty on the cross
section at the $\omega$ and $\phi$ resonances is dominated by the systematic
uncertainty of 2.2%. The resulting cross sections in the 0.62-1.80 GeV energy
range yield $ a_\mu^{3\pi} = 48.91 \pm 0.23~(\mathrm{stat}) \pm
1.07~(\mathrm{syst}) \times 10^{-10} $ for the leading-order hadronic vacuum
polarization contribution to the muon anomalous magnetic moment. This result
differs by $2.5$ standard deviations from the most precise current
determination.
Phys. Rev. Lett. 131, 171803 (2023) 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 $\tau^{}_{D^+_s} = (499.5\pm
1.7\pm 0.9)$ fs, where the first uncertainty is statistical and the second is
systematic. This result is significantly more precise than previous
measurements.
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.
Phys. Rev. D 107, L031103 (2023) We report on a measurement of the $\Omega_c^0$ lifetime using $\Omega_c^0 \to
\Omega^-\pi^+$ decays reconstructed in $e^+e^-\to c\bar{c}$ data collected by
the Belle ...II experiment and corresponding to $207~{\rm fb^{-1}}$ of integrated
luminosity. The result, $\rm\tau(\Omega_c^0)=243\pm48( stat)\pm11(syst)~fs$,
agrees with recent measurements indicating that the $\Omega_c^0$ is not the
shortest-lived weakly decaying charmed baryon.
Physical Review Letters 130, 091902 (2023) We study the processes $e^+e^-\to\omega\chi_{bJ}(1P)$ ($J$ = 0, 1, or 2)
using samples at center-of-mass energies $\sqrt{s}$ = 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 $\Upsilon(4S)$
resonance. We report the first observation of $\omega\chi_{bJ}(1P)$ signals at
$\sqrt{s}$ = 10.745 GeV. By combining Belle II data with Belle results at
$\sqrt{s}$ = 10.867 GeV, we find energy dependencies of the Born cross sections
for $e^+e^-\to \omega\chi_{b1,b2}(1P)$ to be consistent with the shape of the
$\Upsilon(10753)$ state. These data indicate that the internal structures of
the $\Upsilon(10753)$ and $\Upsilon(10860)$ states may differ. Including data
at $\sqrt{s}$ = 10.653 GeV, we also search for the bottomonium equivalent of
the $X(3872)$ state decaying into $\omega\Upsilon(1S)$. No significant signal
is observed for masses between 10.45 and 10.65 GeV/$c^2$.
