We search for CP violation in the charged charm meson decay D+→π+π0, based on a data sample corresponding to an integrated luminosity of 921 fb−1 collected by the Belle experiment at the KEKB e+e− ...asymmetric-energy collider. The measured CP-violating asymmetry is +2.31±1.24(stat)±0.23(syst)%, which is consistent with the standard model prediction and has a significantly improved precision compared to previous results.
We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE air FD is also sensitive to the Cherenkov ...light produced by shower particles. Low-energy cosmic rays, in the PeV energy range, are detectable by TALE as Cherenkov events. Using these events, we measure the energy spectrum from a low energy of ∼2 PeV to an energy greater than 100 PeV. Above 100 PeV, TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than a few EeV. In this paper, we describe the detector, explain the technique, and present results from a measurement of the spectrum using ∼1000 hr of observation. The observed spectrum shows a clear steepening near 1017.1 eV, along with an ankle-like structure at 1016.2 eV. These features present important constraints on the origin of galactic cosmic rays and on propagation models. The feature at 1017.1 eV may also mark the end of the galactic cosmic ray flux and the start of the transition to extragalactic sources.
We study hadronic transitions between bottomonium states using 496 fb−1 data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e− collider. We measure ...B(ϒ(4S)→π+π−ϒ(1S))=(8.2±0.5(stat)±0.4(syst))×10−5, B(ϒ(4S)→π+π−ϒ(2S))=(7.9±1.0(stat)±0.4(syst))×10−5, and B(ϒ(4S)→ηϒ(1S))=(1.70±0.23(stat)±0.08(syst))×10−4. We measure the ratio of branching fractions R=B(ϒ(4S)→ηϒ(1S))/B(ϒ(4S)→π+π−ϒ(1S))=2.07±0.30(stat)±0.11(syst). We search for the decay ϒ(1D31,2)→ηϒ(1S), but do not find significant evidence for such a transition. We also measure the initial-state radiation production cross sections of the ϒ(2S,3S) resonances and we find values compatible with the expected ones. Finally, the analysis of the ϒ(4S)→π+π−ϒ(1S) events shows indications for a resonant contribution due to the f0(980) meson.
We present the results of the first Dalitz plot analysis of the decay D 0 → K-π +η. The analysis is performed on a data set corresponding to an integrated luminosity of 953 fb-1 collected by the ...Belle detector at the asymmetric-energy e+e- KEKB collider. The Dalitz plot is well described by a combination of the six resonant decay channels K- * (892)0 η, K-a0(980)+, K-a2(1320)+, K¯ * (1410)0 η, K* (1680)-π + and K* 2 (1980)-π +, together with Kπ and Kη S-wave components. The decays K* (1680)- → K-η and K* 2 (1980)- → K-η are observed for the first time. We measure ratio of the branching fractions, B(D0→K-π+η) B(D0→K=π+) = 0.500 ± 0.002(stat) ± 0.020(syst) ± 0.003(BPDG). Using the Dalitz fit result, the ratio B(K*(1680)→Kη) B(K*(1680)→Kπ) is measured to be 0.11±0.02(stat)+0.06 =0.04(syst)± 0.04(BPDG); this is much lower than the theoretical expectations (≈ 1) made under the assumption that K* (1680) is a pure 1 3D1 state. The product branching fraction B(D 0 → K* 2 (1980)- → K-ηπ +) = (2.2 +1.7 -1.9 ) × 10-4 is determined. In addition, the πη' contribution to the a0(980)± resonance shape is confirmed with 10.1σ statistical significance using the three-channel Flatté model. We also measure B(D 0 → K¯ * (892)0 η) = (1.41+0.13 -0.12)%. This is consistent with, and more precise than, the current world average (1.02 ± 0.30)%, deviates with a significance of more than 3σ from the theoretical predictions of (0.51-0.92)%.
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