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Register a new userMeasurements in charmless $B$ decays at Belle II
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Riccardo Manfredi
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We report on preliminary measurements of branching fractions, charge-parity-violating asymmetries, and longitudinal polarization fractions in charmless bottom-meson decays from the Belle~II experiment. We use samples of electron-positron collisions collected in 2019 and 2020 at the $Upsilon(4S)$ resonance, corresponding to integrated luminosities of up to 62.8 ${rm fb^{-1}}$. The results are compatible with known values, indicating good understanding of early detector performance.
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We report on the reconstruction of various charmless $B$ decays from electron-positron collisions at the energy corresponding to the $Upsilon(4S)$ resonance collected with the Belle II detector at the SuperKEKB collider. We use simulation to devise optimized event selections and apply them to the full data set collected in 2019, corresponding to 8.7,fb$^{-1}$ of integrated luminosity. We fit the difference between half of the collision energy and the $B$ candidate energy (in the $Upsilon(4S)$ frame) for events restricted to a signal-rich range in beam-energy-constrained mass to search for charmless signals. Signal yields of approximately 80, 15, 20, 30, 90, and 160 decays are reconstructed for the channels $B^0 to K^+pi^-$, $B^0 to pi^+pi^-$, $B^+ to K^0_S(to pi^+pi^-)pi^+$, $B^+ to K^+pi^0(to gammagamma)$, $B^+ to K^+K^-K^+$, and $B^+ to K^+pi^-pi^+$, respectively. Yields and background contaminations are compatible with those expected from simulation and comparable with those obtained by the Belle experiment. The results show a good understanding of the detector performance and offer a reliable basis to assess projections for future reach.
We report on first measurements of branching fractions~($mathcal{B}$) and CP-violating charge asymmetries~($mathcal{A}$) in charmless $B$ decays at Belle~II. We use a sample of electron-positron collisions collected in 2019 and 2020 at the $Upsilon(4S)$ resonance and corresponding to $34.6$,fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $Delta E$ distributions of the resulting samples, restricted in $M_{rm bc}$, are fit to determine signal yields. Signal yields are corrected for efficiencies determined from simulation and control data samples to obtain branching fractions and CP-violating asymmetries for flavour-specific channels. These are the first measurements in charmless decays reported by Belle~II. Results are compatible with known determinations and show detector performance comparable with the best Belle results offering a reliable basis to assess projections for future reach.
Rare and flavour-changing neutral current decays of the B meson are an important probe in the search for physics beyond the Standard Model. There have recently been several anomalies in rare B decays, and lepton-universality measurements, specifically involving the $bto sell^+ell^-$ quark transition. These results tend towards a non-Standard-Model interpretation. The Belle II experiment is a next-generation b physics experiment located at SuperKEKB, an upgraded B factory $e^+e^-$ collider, in Tsukuba, Japan. The first collisions are expected in early 2018 with full physics data expected in 2019. This document describes prospects for several rare B decays at Belle II including $bto sell^+ell^-$ processes and others, such as $bto(s,,d)gamma$ and $bto s ubar u$. Areas where the Belle II program is complementary to that of the currently running LHCb experiment are highlighted.
We present new results from the study of B decays at SLD: a measurement of the inclusive double-charm branching fraction in B-hadron decays and a search for the rare exclusive charmless decays B+ --> Rho0 Pi+(K+) and B+ --> K*0 Pi+(K+). Using a novel technique which consists of counting charged kaons produced at the secondary (B) vertex and the tertiary (D) vertex, we measure BR(B-->DDbarX) = 0.188 +- 0.025(stat) +- 0.059(syst). Another technique, based on the comparison of the charge of the D vertex to the flavor of the B hadron at production, yields a consistent result. In the search for rare exclusive B+ decays, no candidates were found and competitive branching ratio upper limits are derived.
We report a study of the charmless hadronic decay of the charged $B$ meson to the three-body final state $K^+ K^- pi^+$. The results are based on a data sample that contains $772times10^6$ $B bar{B}$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The measured inclusive branching fraction and the direct $CP$ asymmetry are $(5.38pm0.40pm0.35)times 10^{-6}$ and $-0.170pm0.073pm0.017$, respectively, where the first uncertainties are statistical and the second are systematic. The $K^{+}K^{-}$ invariant mass distribution of the signal candidates shows an excess in the region below $1.5$ GeV/$c^2$, which is consistent with the previous studies from BaBar and LHCb. In addition, strong evidence of a large direct $CP$ asymmetry is found in the $K^{+}K^{-}$ low-invariant-mass region.
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