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 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.
A series of data samples was collected with the Belle II detector at the SuperKEKB collider from March 2019 to June 2022. We determine the integrated luminosities of these data samples using three ...distinct methodologies involving Bhabha (\(e^+e^- \to e^+e^-(n\gamma)\)), digamma (\(e^+e^- \to \gamma\gamma(n\gamma)\)), and dimuon (\(e^+e^- \to \mu^+ \mu^- (n\gamma)\)) events. The total integrated luminosity obtained with Bhabha, digamma, and dimuon events is (426.52 \(\pm\) 0.03 \(\pm\) 2.48)~fb\(^{-1}\), (427.32 \(\pm\) 0.03 \(\pm\) 2.56)~fb\(^{-1}\), and (424.84 \(\pm\) 0.04 \(\pm\) 3.88)~fb\(^{-1}\), where the first uncertainties are statistical and the second are systematic. The resulting total integrated luminosity obtained from the combination of the three methods is (426.88 \(\pm\) 1.93)~fb\(^{-1}\).
We present a measurement of $|V_{ub}|$ from a simultaneous study of the
charmless semileptonic decays $B^0\to\pi^- \ell^+ \nu_{\ell}$ and $B^+\to\rho^0
\ell^+\nu_{\ell}$, where $\ell = e, \mu$. This ...measurement uses a data sample
of 387 million $B\overline{B}$ meson pairs recorded by the Belle~II detector at
the SuperKEKB electron-positron collider between 2019 and 2022. The two decays
are reconstructed without identifying the partner $B$ mesons. We simultaneously
measure the differential branching fractions of $B^0\to\pi^- \ell^+ \nu_{\ell}$
and $B^+\to\rho^0 \ell^+\nu_{\ell}$ decays as functions of $q^2$ (momentum
transfer squared). From these, we obtain total branching fractions
$B(B^0\to\pi^- \ell^+ \nu_{\ell}) = (1.516 \pm 0.042 (\mathrm{stat}) \pm 0.059
(\mathrm{syst})) \times 10^{-4}$ and $B(B^+\to\rho^0 \ell^+\nu_{\ell}) = (1.625
\pm 0.079 (\mathrm{stat}) \pm 0.180 (\mathrm{syst})) \times 10^{-4}$. By
fitting the measured $B^0\to\pi^- \ell^+ \nu_{\ell}$ partial branching
fractions as functions of $q^2$, together with constraints on the
non-perturbative hadronic contribution from lattice QCD calculations, we obtain
$|V_{ub}|$ = $(3.93 \pm 0.09 \pm 0.13 \pm 0.19) \times 10^{-3}$. Here, the
first uncertainty is statistical, the second is systematic, and the third is
theoretical.
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 measurements of time-dependent $CP$ asymmetries in $B^0 \to K^0_S
\pi^0 \gamma$ decays based on a data sample of $(388\pm6)\times10^6$ $B\bar{B}$
events collected at the $\Upsilon(4S)$ ...resonance with the Belle II detector.
The Belle II experiment operates at the SuperKEKB asymmetric-energy $e^+e^-$
collider. We measure decay-time distributions to determine $CP$-violating
parameters $S$ and $C$. We determine these parameters for two ranges of $K^0_S
\pi^0$ invariant mass: $m(K^0_S \pi^0)\in (0.8, 1.0)$ $GeV/c^2$, which is
dominated by $B^0 \to K^{*0} (\to K^0_S \pi^0) \gamma$ decays, and a
complementary region $m(K^0_S \pi^0)\in (0.6, 0.8)\cup(1.0, 1.8)$ $GeV/c^2$.
Our results have improved precision as compared to previous measurements and
are consistent with theory predictions.
We present measurements of $B^{+}\rightarrow\rho^{+}\gamma$ and
$B^{0}\rightarrow\rho^{0}\gamma$ decays using a combined data sample of $772
\times 10^6$ $B\overline{B}$ pairs collected by the Belle ...experiment and
$387\times 10^6$ $B\overline{B}$ pairs collected by the Belle II experiment in
$e^{+}e^{-}$ collisions at the $\Upsilon (4S)$ resonance. After an optimized
selection, a simultaneous fit to the Belle and Belle II data sets yields
$114\pm 12$ $B^{+}\rightarrow\rho^{+}\gamma$ and $99\pm 12$
$B^{0}\rightarrow\rho^{0}\gamma$ decays. The measured branching fractions are
$(13.1^{+2.0 +1.3}_{-1.9 -1.2})\times 10^{-7}$ and $(7.5\pm
1.3^{+1.0}_{-0.8})\times 10^{-7}$ for $B^{+}\rightarrow\rho^{+}\gamma$ and
$B^{0}\rightarrow\rho^{0}\gamma$ decays, respectively, where the first
uncertainty is statistical and the second is systematic. We also measure the
isospin asymmetry $A_{\rm I}(B\rightarrow\rho\gamma)=(10.9^{+11.2 +7.8}_{-11.7
-7.3})\%$ and the direct CP asymmetry
$A_{CP}(B^{+}\rightarrow\rho^{+}\gamma)=(-8.2\pm 15.2^{+1.6}_{-1.2})\%$.
