We present the first experimental limits on high-q2 contributions to charmless semileptonic decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias ...determinations of /Vub/ from inclusive measurements of B-->Xulupsilon. Using a wide range of models based on available theoretical input we set a limit of GammaWA/Gammab-->u<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of /Vub/.
We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass ...energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively.
The first measurements of differential branching fractions of inclusive semileptonic \({B \to X_u \, \ell^+\, \nu_{\ell}}\) decays are performed using the full Belle data set of 711 fb\(^{-1}\) of ...integrated luminosity at the \(\Upsilon(4S)\) resonance and for \(\ell = e, \mu\). Differential branching fractions are reported as a function of the lepton momentum, the four-momentum-transfer squared, light-cone momenta, the hadronic mass, and the hadronic mass squared. They are obtained by subtracting the backgrounds from semileptonic \({B \to X_c \, \ell^+\, \nu_{\ell}}\) decays and other processes, and corrected for resolution and acceptance effects. The measured distributions are compared to predictions from inclusive and hybrid \({B \to X_u \, \ell^+\, \nu_{\ell}}\) calculations.
Phys. Rev. Lett. 130, 071804 (2023) The dark photon $A^\prime$ and the dark Higgs boson $h^\prime$ are
hypothetical particles predicted in many dark sector models. We search for the
simultaneous ...production of $A^\prime$ and $h^\prime$ in the dark Higgsstrahlung
process $e^{+}e^{-}\rightarrow A^\prime \, h^\prime$ with $A^\prime \rightarrow
\mu^+\mu^-$ and $ h^\prime$ invisible in electron-positron collisions at a
center-of-mass energy of 10.58 GeV collected by the Belle II experiment in
2019. With an integrated luminosity of 8.34 fb$^{-1}$, we observe no evidence
for signal. We obtain exclusion limits at 90% Bayesian credibility in the range
of 1.7--5.0 fb on the cross section and in the range of $1.7
\times10^{-8}$--$200 \times10^{-8}$ on the effective coupling $\varepsilon^2
\times \alpha_D$ for the $A^\prime$ mass in the range of 4.0 GeV/$c^2$ $<
M_{A^\prime}< 9.7$ GeV/$c^2$ and for the $h^\prime$ mass $M_{h^\prime} <
M_{A^\prime}$, where $\varepsilon$ is the mixing strength between the standard
model and the dark photon and $\alpha_D$ is the coupling of the dark photon to
the dark Higgs boson. Our limits are the first in this mass range.
Phys. Rev. D 105, 012007 (2022) We report results from a search for the decay $B_s^0\rightarrow\eta\eta$
using 121.4 fb$^{-1}$ of data collected at the $\Upsilon(5S)$ resonance with
the Belle ...detector at the KEKB asymmetric-energy $e^+e^-$ collider. We do not
observe any signal and set an upper limit on the branching fraction of
$14.3\times 10^{-5}$ at $90\%$ confidence level. This result represents a
significant improvement over the previous most stringent limit.
Phys. Rev. Lett. 130, 071802 (2023) An absolute measurement of the $\Lambda^{+}_c$ lifetime is reported using
$\Lambda_c^+\rightarrow pK^-\pi^+$ 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 $\Upsilon(4S)$
resonance, is $207.2~\mbox{fb}^{-1}$. The result, $\tau(\Lambda^{+}_c) = 203.20
\pm 0.89 \,\mathrm{(stat)} \pm 0.77 \,\mathrm{(syst)}$ fs, is the most precise
measurement to date and is consistent with previous determinations.
We observe signals for the decays psi(3770) --> XJ/psi from data acquired with the CLEO detector operating at the CESR e+ e- collider with square root of s = 3773 MeV. We measure the following ...branching fractions Beta(psi(3770) --> XJ/psi and significances: (189 +/- 20 +/- 20) x 10(-5) (11.6sigma) for X = pi+ pi-, (80 +/- 25 +/- 16) x 10(-5) (3.4sigma) for X = pi0 pi0, and (87 +/- 33 +/- 22) x 10(-5) (3.5sigma) for X = eta, where the errors are statistical and systematic, respectively. The radiative return process e+ e- --> gamma psi(2S) populates the same event sample and is used to measure Gamma eepsi(2S) = (2.54 +/- 0.03 +/- 0.11) keV.
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.
Phys. Rev. D 106, 012006 (2022) We report the first search for the penguin-dominated process $B^0 \rightarrow
K_S^0 K_S^0 \gamma$ using the full data sample of $772\times 10^6$ $B\bar{B}$
pairs ...collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$
collider. We do not observe any statistically significant signal yield in the
$K_S^0$-pair invariant mass range 1 GeV/$c^2 < M_{K_S^0 K_S^0} < $ 3 GeV/$c^2$,
and set the following upper limits at 90% confidence level: $\mathcal{B}(B^0
\to K_S^0 K_S^0 \gamma) < 5.8\times10^{-7}$, $\mathcal{B}(B^0 \to f_2
\gamma)\times \mathcal{B}(f_2 (1270) \to K_S^0 K_S^0 ) < 3.1\times10^{-7}$, and
$\mathcal{B}(B^0 \to f_2^{\prime} \gamma)\times \mathcal{B}(f_2^{\prime} (1525)
\to K_S^0 K_S^0 ) < 2.1\times10^{-7}$. Further, 90% confidence upper limits
have also been set in the range of 0.7-2.9$\times10^{-7}$ on the $B^0
\rightarrow K_S^0 K_S^0 \gamma$ branching fraction in bins of $M_{K_S^0
K_S^0}$.
We find evidence for the semileptonic baryonic decay B-→pp¯ℓ-ν¯ℓ (ℓ=e, μ), based on a data sample of 772 million BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB ...asymmetric-energy electron-positron collider. A neural-network based hadronic B-meson tagging method is used in this study. The branching fraction of B-→pp¯ℓ-ν¯ℓ is measured to be (5.8+2.4-2.1(stat)±0.9(syst))×10-6 with a significance of 3.2σ, where lepton universality is assumed. We also estimate the corresponding upper limit: B(B-→pp¯ℓ-ν¯ℓ)<9.6×10-6 at the 90% confidence level. This measurement helps constrain the baryonic transition form factor in B decays
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