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.
We present the results of a search for the \(b \to d\ell^+\ell^-\) flavor-changing neutral-current rare decays \(B^{+, 0} \to (\eta, \omega, \pi^{+,0}, \rho^{+, 0}) e^+e^-\) and \(B^{+, 0} \to (\eta, ...\omega, \pi^{0}, \rho^{+}) \mu^+\mu^-\) using a \(711\) fb\(^{-1}\) data sample that contains \(772 \times 10^{6}\) \(B\overline{B}\) events. The data were collected at the \(\Upsilon(4S)\) resonance with the Belle detector at the KEKB asymmetric-energy \(e^+e^-\) collider. We find no evidence for signal and set upper limits on branching fractions at the \(90\%\) confidence level in the range \((3.8 - 47) \times 10^{-8}\) depending on the decay channel. The obtained limits are the world's best results. This is the first search for the channels \(B^{+, 0} \to (\omega, \rho^{+,0}) e^+e^-\) and \(B^{+, 0} \to (\omega, \rho^{+})\mu^+\mu^-\).
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.
We describe a measurement of charge-parity (\(CP\)) violation asymmetries in \(B^0\to\eta'K^0_S\) decays using Belle II data. We consider \(\eta'\to\eta(\to\gamma\gamma)\pi^+\pi^-\) and ...\(\eta'\to\rho(\to\pi^+\pi^-)\gamma\) decays. The data were collected at the SuperKEKB asymmetric-energy \(e^+e^-\) collider between the years 2019 and 2022, and contain \((387\pm 6) \times 10^6\) bottom-antibottom meson pairs. We reconstruct \(829\pm35\) signal decays and extract the \(CP\) violating parameters from a fit to the distribution of the proper-decay-time difference between the two \(B\) mesons. The measured direct and mixing-induced \(CP\) asymmetries are \(\text{C}_{\eta'K^0_S} = -0.19 \pm 0.08 \pm 0.03 \) and \(\text{S}_{\eta'K^0_S} = +0.67 \pm 0.10 \pm 0.04 \), respectively, where the first uncertainties are statistical and the second are systematic. These results are in agreement with current world averages and standard model predictions.
The ratio of branching fractions \(R(D^{*}) = \mathcal{B}(\overline{B} \rightarrow D^{*} \tau^{-} \overline{\nu}_{\tau})\)/\(\mathcal{B} (\overline{B} \rightarrow D^{*} \ell^{-} ...\overline{\nu}_{\ell})\), where \(\ell\) is an electron or muon, is measured using a Belle~II data sample with an integrated luminosity of \(189~\mathrm{fb}^{-1}\) at the SuperKEKB asymmetric-energy \(e^{+} e^{-}\) collider. Data is collected at the \(\Upsilon(\mathrm{4S})\) resonance, and one \(B\) meson in the \(\Upsilon(\mathrm{4S})\rightarrow B\overline{B}\) decay is fully reconstructed in hadronic decay modes. The accompanying signal \(B\) meson is reconstructed as \(\overline{B}\rightarrow D^{*} \tau^{-}\overline{\nu}_{\tau}\) using leptonic \(\tau\) decays. The normalization decay, \(\overline{B}\rightarrow D^{*} \ell^{-} \overline{\nu}_{\ell}\), where \(\ell\) is an electron or muon, produces the same observable final state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields \(R(D^{*}) = 0.262~_{-0.039}^{+0.041}(\mathrm{stat})~_{-0.032}^{+0.035}(\mathrm{syst})\). This result is consistent with the current world average and with standard model predictions.
We search for the \(e^+e^-\to\eta_b(1S)\omega\) and \(e^+e^-\to\chi_{b0}(1P)\omega\) processes at a center-of-mass energy of 10.745 GeV, which is close to the peak of the \(\Upsilon(10753)\) state. ...We use data collected by the Belle II experiment during a special run, corresponding to an integrated luminosity of \(9.8\,\mathrm{fb}^{-1}\). We reconstruct \(\omega\to\pi^+\pi^-\pi^0\) decays and use the \(\omega\) meson's recoil mass to search for the signals. We do not find evidence for either process, and set upper limits on the corresponding Born-level cross sections of 2.5 pb and 7.8 pb, respectively, at the 90% confidence level. The \(\chi_{b0}(1P)\omega\) limit is the result of a combination of this analysis and a previous search using full reconstruction.
We measure the tau-to-light-lepton ratio of inclusive \(B\)-meson branching fractions \(R(X_{\tau/\ell}) \equiv \mathcal{B}(B\to X \tau \nu)/\mathcal{B}(B \to X \ell \nu)\), where \(\ell\) indicates ...an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed \(B\) meson and a charged lepton candidate from \(189~\mathrm{fb}^{-1}\) of electron-positron collision data collected with the Belle II detector. We find \(R(X_{\tau/\ell}) = 0.228 \pm 0.016~(\mathrm{stat}) \pm 0.036~(\mathrm{syst})\), in agreement with standard-model expectations. This is the first direct measurement of \(R(X_{\tau/\ell})\).
We present a measurement of time-dependent rate asymmetries in \(B^0\to \phi K^0_S\) decays to search for non-standard-model physics in \(b\to q \overline{q}s\) transitions. The data sample is ...collected with the Belle II detector at the SuperKEKB asymmetric-energy \(e^{+}e^{-}\) collider in 2019-2022 and contains \((387\pm 6)\times 10^6\) bottom-antibottom mesons from \(\Upsilon(4S)\) resonance decays. We reconstruct \(162\pm17\) signal events and extract the charge-parity (\(CP\)) violating parameters from a fit to the distribution of the proper-decay-time difference of the two \(B\) mesons. The measured direct and mixing-induced \(CP\) asymmetries are \(A=0.31\pm0.20\pm0.05\) and \(S=0.54\pm0.26^{+0.06}_{-0.08}\), respectively, where the first uncertainties are statistical and the second are systematic. The results are compatible with the \(CP\) asymmetries observed in \(b\to c\overline{c} s\) transitions.
The Belle II Physics Book Urquijo, P; Bigi, I I; Bona, M ...
arXiv.org,
09/2019
Paper, Journal Article
Odprti dostop
We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB \(e^+e^-\) collider. Belle II collected its first collisions in 2018, and is expected to operate ...for the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic B decays, Radiative and Electroweak penguins, phi_1 and phi_2 (time-dependent CP violation) measurements, phi_3 measurements, Charmless hadronic B decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.
We report results from a study of \(B^\pm \rightarrow DK^\pm\) decays followed by \(D\) decaying to \(CP\)~eigenstates, where \(D\) indicates a \(D^0\) or \(\bar{D}^{0}\) meson. These decays are ...sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle \(\phi_{3}\). The results are based on a combined analysis of the final data set of \(772 \times 10^6~B\bar{B}\) pairs collected by the Belle experiment and a data set of \(198 \times 10^6~B\bar{B}\) pairs collected by the Belle~II experiment, both in electron-positron collisions at the \(\Upsilon(4S)\) resonance. We measure the \(CP\) asymmetries to be \(\mathcal{ A}_{CP +} =~(+12.5 \pm 5.8 \pm 1.4)\% \) and \(\mathcal{ A}_{CP -} =~(-16.7 \pm 5.7 \pm 0.6)\%\), and the ratios of branching fractions to be \(\mathcal{ R}_{CP+}=~1.164 \pm 0.081 \pm 0.036 \) and \(\mathcal{ R}_{CP-} =~1.151 \pm 0.074 \pm 0.019\). The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries \(\mathcal{A}_{CP +}\) and \(\mathcal{A}_{CP -}\) have similar magnitudes and opposite signs; their difference corresponds to 3.5~standard deviations. From these values we calculate 68.3\% confidence intervals of (\(8.5^{\circ}<\phi_{3}<16.5^{\circ}\)) or (\(84.5^{\circ}<\phi_{3}<95.5^{\circ}\)) or (\(163.3^{\circ}<\phi_{3}<171.5^{\circ}\)) and \(0.321<r_{B}<0.465\).
