We report a search for a dark vector gauge boson \(U^\prime\) that couples to quarks in the decay chain \(D^{*+} \to D^0 \pi^+, D^0 \to K^0_S \eta, \eta \to U^\prime \gamma\), \(U^\prime \to \pi^+ ...\pi^-\). No signal is found and we set a mass-dependent limit on the baryonic fine structure constant of \(10^{-3} - 10^{-2}\) in the \(U^\prime\) mass range of 290 to 520 MeV/\(c^2\). This analysis is based on a data sample of 976 fb\(^{-1}\) collected by the Belle experiment at the KEKB asymmetric-energy \(e^+e^-\) collider.
We report branching fraction measurements of the decays B+→ηℓ+νℓ and B+→η′ℓ+νℓ based on 711 fb-1 of data collected near the ϒ(4S) resonance with the Belle experiment at the KEKB asymmetric-energy ...e+e- collider. This data sample contains 772 million BB¯ events. One of the two B mesons is fully reconstructed in a hadronic decay mode. Among the remaining (“signal-B”) daughters, we search for the η meson in two decay channels, η→γγ and η→π+π-π0, and reconstruct the η′ meson in η′→ηπ+π- with subsequent decay of the η into γγ. Combining the two η modes and using an extended maximum likelihood, the B+→ηℓ+νℓ branching fraction is measured to be (4.2±1.1(stat.)±0.3(syst.))×10−5. For B+→η′ℓ+νℓ, we observe no significant signal and set an upper limit of 0.72×10-4 at 90% confidence level.
We present a measurement of the branching fraction and the longitudinal polarization fraction of \(B^{0}\rightarrow\rho^+\rho^-\) decays, as well as the time-dependent \(CP\) violating parameters in ...decays into longitudinally polarized \(\rho^{+}\rho^{-}\) pairs with Belle's final data set of \(772\times 10^6\) \(B\bar{B}\) pairs, at the \(\Upsilon(4S)\) resonance, collected at the asymmetric-energy \(e^+ e^-\) collider KEKB. We obtain \({\cal B}(B^0 \rightarrow \rho^+ \rho^-)=(28.3\pm 1.5\;(\rm stat) \pm 1.5\;(\rm syst))\times 10^{-6}\), \(f_L = 0.988\pm 0.012\;(\rm stat ) \pm0.023\;(\rm syst)\), \({\cal A}_{CP} = 0.00\pm0.10\;(\rm stat ) \pm0.06\;(\rm syst)\), \({\cal S}_{CP} = -0.13\pm0.15\;(\rm stat ) \pm0.05\;(\rm syst).\) We perform an isospin analysis to constrain the CKM angle \(\phi_2\) and obtain two solutions with \begin{eqnarray} \phi_{2} = (93.7\pm10.6)^{\circ},\nonumber \end{eqnarray} being most compatible with other Standard-Model based fits to the data.
Using a data sample of 980 \({\rm fb}^{-1}\) of \(e^+e^-\) annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy \(e^+e^-\) collider, we report the results of a ...study of excited \(\Xi_c\) states that decay, via the emission of photons and/or charged pions, into \(\Xi_c^0\) or \(\Xi_c^+\) ground state charmed-strange baryons. We present new measurements of the masses of all members of the \(\Xi_c^{\prime}\), \(\Xi_c(2645)\), \(\Xi_c(2790)\), \(\Xi_c(2815)\), and \(\Xi_c(2980)\) isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.
We report a measurement of the CP violation parameter \(\varphi_1\) obtained in a time-dependent analysis of \(B^0\to\bar{D}{}^{(*)0}h^0\) decays followed by \(\bar{D}{}^0\to K_S^0\pi^+\pi^-\) decay. ...A model-independent measurement is performed using the binned Dalitz plot technique. The measured value is \(\varphi_1 = 11.7^{\circ}\pm7.8^{\circ}({\rm stat.})\pm 2.1^{\circ}({\rm syst.})\). Treating \(\sin{2\varphi_1}\) and \(\cos{2\varphi_1}\) as independent parameters, we obtain \(\sin{2\varphi_1} = 0.43\pm 0.27({\rm stat.})\pm 0.08({\rm syst.})\) and \(\cos{2\varphi_1} = 1.06\pm 0.33({\rm stat.})^{+0.21}_{-0.15}({\rm syst.})\). The results are obtained with a full data sample of \(772 \times 10^6 B\bar{B}\) pairs collected near the \(\Upsilon(4S)\) resonance with the Belle detector at the KEKB asymmetric-energy \(e^+e^-\) collider.
We report inclusive and exclusive measurements for \(\chi_{c1}\) and \(\chi_{c2}\) production in \(B\) decays. We measure \(\mathcal{B}(B \to \chi_{c1} X)\)= \((3.03 \pm 0.05(\mbox{stat}) \pm ...0.24(\mbox{syst})) \times 10^{-3}\) and \(\mathcal{B}(B \to \chi_{c2} X)\)= \((0.70 \pm 0.06(\mbox{stat}) \pm 0.10(\mbox{syst})) \times 10^{-3}\). For the first time, \(\chi_{c2}\) production in exclusive \(B\) decays in the modes \(B^0 \to \chi_{c2}\pi^- K^+\) and \(B^+ \to \chi_{c2} \pi^+ \pi^- K^+\) has been observed, along with first evidence for the \(B^+ \to \chi_{c2} \pi^+ K_S^0\) decay mode. For \(\chi_{c1}\) production, we report the first observation in the \(B^+ \to \chi_{c1} \pi^+ \pi^- K^+\), \(B^0 \to \chi_{c1} \pi^+ \pi^- K_S^0\) and \(B^0 \to \chi_{c1} \pi^0 \pi^- K^+\) decay modes. Using these decay modes, we observe a difference in the production mechanism of \(\chi_{c2}\) in comparison to \(\chi_{c1}\) in \(B\) decays. In addition, we report searches for \(X(3872)\) and \(\chi_{c1}(2P)\) in the \(B^+ \to (\chi_{c1} \pi^+ \pi^-) K^+\) decay mode. The reported results use \(772 \times 10^{6}\) \(B\overline{B}\) events collected at the \(\Upsilon(4S)\) resonance with the Belle detector at the KEKB asymmetric-energy \(e^+e^-\) collider.
We present a search for a non-Standard-Model invisible particle \(X^0\) in the mass range \(0.1\textrm{-}1.8 \,{\rm GeV}/{c^2}\) in \(B^{+}\to e^{+} X^{0}\) and \(B^{+}\to \mu^{+} X^{0}\) decays. The ...results are obtained from a \(711~{\rm fb}^{-1}\) data sample that corresponds to \(772 \times 10^{6} B\bar{B}\) pairs, collected at the \(\Upsilon(4S)\) resonance with the Belle detector at the KEKB \(e^+ e^-\) collider. One \(B\) meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner \(B\) meson. We find no evidence of a signal and set upper limits on the order of \(10^{-6}\).
Using data collected with the Belle detector at the KEKB asymmetric-energy \(e^+e^-\) collider, we measure the energy dependence of the \(e^+e^- \to h_b(nP)\pi^+\pi^-\) \((n=1,2)\) cross sections ...from thresholds up to \(11.02\,\)GeV. We find clear \(\Upsilon(10860)\) and \(\Upsilon(11020)\) peaks with little or no continuum contribution. We study the resonant substructure of the \(\Upsilon(11020) \to h_b(nP)\pi^+\pi^-\) transitions and find evidence that they proceed entirely via the intermediate isovector states \(Z_b(10610)\) and \(Z_b(10650)\). The relative fraction of these states is loosely constrained by the current data: the hypothesis that only \(Z_b(10610)\) is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only \(Z_b(10650)\) is produced is not excluded at a significant level.
The process \(\gamma \gamma \to p \bar{p} K^+ K^-\) and its intermediate processes are measured for the first time using a 980~fb\(^{-1}\) data sample collected with the Belle detector at the KEKB ...asymmetric-energy \(e^+e^-\) collider. The production of \(p \bar{p} K^+ K^-\) and a \(\Lambda(1520)^0~(\bar{\Lambda}(1520)^0)\) signal in the \(pK^-\)~(\(\bar{p} K^+\)) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540~MeV/\(c^2\), denoted as \(\Theta(1540)^0\)~(\(\bar{\Theta}~(1540)^0\)) or \(\Theta(1540)^{++}\)~(\(\Theta(1540)^{--}\)), is seen in the \(p K^-\)~(\(\bar{p}K^+\)) or \(pK^+\)~(\(\bar{p} K^-\)) invariant mass spectra. Cross sections for \(\gamma \gamma \to p \bar{p} K^+ K^-\), \(\Lambda(1520)^0 \bar{p} K^+ +c.c.\) and the products \(\sigma(\gamma \gamma \to \Theta(1540)^0 \bar{p} K^+ +c.c.)\BR(\Theta(1540)^0 \to p K^{-})\) and \(\sigma(\gamma \gamma \to \Theta(1540)^{++} \bar{p} K^- +c.c.)\BR(\Theta(1540)^{++}\to p K^{+})\) are measured. We also determine upper limits on the products of the \(\chi_{c0}\) and \(\chi_{c2}\) two-photon decay widths and their branching fractions to \(p \bar{p} K^+ K^-\) at the 90\% credibility level.
We search for the process \(B^0 \to \pi^- \tau^+ \nu_\tau\) using the full Belle data set of \(711\,{\rm fb}^{-1}\), corresponding to \(772 \times 10^6 B\bar{B}\) pairs, collected at the ...\(\Upsilon(4S)\) resonance with the Belle detector at the KEKB asymmetric-energy \(e^+ e^-\) collider. We reconstruct one \(B\) meson in a hadronic decay and search for the \(B^0 \to \pi^- \tau^+ \nu_\tau\) process in the remainder of the event. No significant signal is observed and an upper limit of \(\mathcal{B}(B^0 \to \pi^- \tau^+ \nu_\tau) < 2.5 \times 10^{-4}\) is obtained at the \(90\%\) confidence level.
