Study of the process e+e−→ηπ0γe^+e^- \to \eta\pi^0\gamma in the energy range \sqrt{s} = \mbox{1.05-2.00} GeV with the SND detector

The process $e^+e^-\to\eta\pi^0\gamma$ is studied in the center-of-mass energy range 1.05-2.00 GeV using data with an integrated luminosity of 94.5 pb$^{-1}$ collected by the SND detector at the VEPP-2000 $e^+e^-$ collider. The $e^+e^-\to\eta\pi^0\gamma$ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $\omega\eta$ intermediate state. The measured cross section of the subprocess $e^+e^-\to\omega\eta\to\eta\pi^0\gamma$ is consistent with previous measurements in the $e^+e^-\to\pi^+\pi^-\pi^0\eta$ mode. It is found, with a significance of 5.6$\sigma$, that the process $e^+e^-\to\eta\pi^0\gamma$ is not completely described by hadronic vector-pseudoscalar intermediate states. The cross section of this missing contribution, which can originate from radiation processes, e. g. $e^+e^-\to a_{0}(1450)\gamma$, is measured. It is found to be 15-20 pb in the wide energy range from 1.3 to 1.9 GeV.Comment: 10 pages, 6 figures, to be submitted to European Physical Journal

Study of dynamics of the process e+e−→π+π−π0e^+e^-\to \pi^+\pi^-\pi^0 in the energy range 1.15--2.00 GeV

The dynamics of the process $e^+e^- \to \pi^+\pi^-\pi^0$ is studied in the energy region from 1.15 to 2.00 GeV using data accumulated with the SND detector at the VEPP-2000 $e^+e^-$ collider. The Dalitz plot distribution and $\pi^+\pi^-$ mass spectrum are analyzed in a model including the intermediate states $\rho(770)\pi$, $\rho(1450)\pi$, and $\omega\pi^0$. As a result, the energy dependences of the $\rho(770)\pi$ and $\rho(1450)\pi$ cross sections and the relative phases between the $\rho(770)\pi$ amplitude and the $\rho(1450)\pi$ and $\omega\pi^0$ amplitudes are obtained. The $\rho(1450)\pi$ cross section has a peak in the energy region of the $\omega(1650)$ resonance (1.55-1.75 GeV). In this energy range the contributions of the $\rho(770)\pi$ and $\rho(1450)\pi$ states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the $\rho(770)\pi$ cross section. We conclude that the intermediate state $\rho(1450)\pi$ gives a significant contribution to the decay of $\omega (1650)\to\pi^+\pi^-\pi^0$, whereas the $\rho(770)\pi$ mechanism dominates in the decay $\omega(1420)\to\pi^+\pi^-\pi^0$.Comment: 9 pages, 7 figures, 3 table

Dalitz analysis of D0→K−π+ηD^{0}\to K^{-}\pi^{+}\eta decays at Belle

We present the results of the first Dalitz plot analysis of the decay $D^{0}\to K^{-}\pi^{+}\eta$. The analysis is performed on a data set corresponding to an integrated luminosity of 953 $\rm{fb}^{-1}$ 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 $\bar{K}^{*}(892)^0\eta$, $K^{-}a_0(980)^+$, $K^{-}a_2(1320)^+$, $\bar{K}^{*}(1410)^0\eta$, $K^{*}(1680)^-\pi^{+}$ and $K_2^{*}(1980)^-\pi^{+}$, together with $K\pi$ and $K\eta$ S-wave components. The decays $K^{*}(1680)^{-}\to K^{-}\eta$ and $K_{2}^{*}(1980)^{-}\to K^{-}\eta$ are observed for the first time. We measure ratio of the branching fractions, $\frac{\mathcal{B}(D^{0}\to K^{-}\pi^{+}\eta)}{\mathcal{B}(D^{0}\to K^{-}\pi^{+})}=0.500\pm0.002{\rm(stat)}\pm0.020{\rm(syst)}\pm0.003{\rm (\mathcal{B}_{PDG})}$. Using the Dalitz fit result, the ratio $\frac{\mathcal{B}(K^{*}(1680)\to K\eta)}{\mathcal{B}(K^{*}(1680)\to K\pi)}$ is measured to be $0.11\pm0.02{\rm(stat)}^{+0.06}_{-0.04}{\rm(syst)}\pm0.04{\rm(\mathcal{B}_{\text{PDG}})}$; this is much lower than the theoretical expectations ($\approx1$) made under the assumption that $K^{*}(1680)$ is a pure $1^{3}D_1$ state. The product branching fraction $\mathcal{B}(D^0\to [K_2^{*}(1980)^-\to K^{-}\eta]\pi^{+})=(2.2^{+1.7}_{-1.9})\times10^{-4}$ is determined. In addition, the $\pi\eta^{\prime}$ contribution to the $a_0(980)^{\pm}$ resonance shape is confirmed with 10.1$\sigma$ statistical significance using the three-channel Flatt\'{e} model. We also measure $\mathcal{B}(D^0\to\bar{K}^{*}(892)^0\eta)=(1.41^{+0.13}_{-0.12})\%$. This is consistent with, and more precise than, the current world average $(1.02\pm0.30)\%$, deviates with a significance of more than $3\sigma$ from the theoretical predictions of (0.51-0.92)%.Comment: 11 pages, 2 figure

Test of lepton flavor universality and search for lepton flavor violation in B → Kℓℓ decays

We present measurements of the branching fractions for the decays B → Kμ$^{+}$μ$^{-}$ and B → Ke$^{+}$e$^{-}$, and their ratio (RK), using a data sample of 711 fb$^{-1}$ that contains 772 × 10$^{6}$ B$\overline{B}$ events. The data were collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e$^{+}$e$^{-}$ collider. The ratio RK is measured in five bins of dilepton invariant-mass-squared (q$^{2}$): q$^{2}$ ∈ (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV$^{2}$/c$^{4}$, along with the whole q$^{2}$ region. The R$_{K}$ value for q$^{2}$ ∈ (1.0, 6.0) GeV$^{2}$/c$^{4}$ is 1.03$\substack{+0.28\\-0.24}$ ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for R$_{K}$ are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q$^{2}$ bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q$^{2}$ ∈ (1.0, 6.0) GeV$^{2}$/c$^{4}$ bin in the mode with muon final states. The measured differential branching fractions, dB/dq$^{2}$, are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ$^{±}$e$^{∓}$ decays and set 90% confidence-level upper limits on the branching fraction in the range of 10$^{-8}$ for B$^{+}$ → K$^{+}$μ$^{±}$e$^{∓}$, and B$^{0}$ → K$^{0}$μ$^{±}$e$^{∓}$ modes

Test of lepton flavor universality and search for lepton flavor violation in B → Kℓℓ decays

We present measurements of the branching fractions for the decays B → Kμ$^{+}$μ$^{-}$ and B → Ke$^{+}$e$^{-}$, and their ratio (RK), using a data sample of 711 fb$^{-1}$ that contains 772 × 10$^{6}$ B$\overline{B}$ events. The data were collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e$^{+}$e$^{-}$ collider. The ratio RK is measured in five bins of dilepton invariant-mass-squared (q$^{2}$): q$^{2}$ ∈ (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV$^{2}$/c$^{4}$, along with the whole q$^{2}$ region. The R$_{K}$ value for q$^{2}$ ∈ (1.0, 6.0) GeV$^{2}$/c$^{4}$ is 1.03$\substack{+0.28\\-0.24}$ ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for R$_{K}$ are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q$^{2}$ bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q$^{2}$ ∈ (1.0, 6.0) GeV$^{2}$/c$^{4}$ bin in the mode with muon final states. The measured differential branching fractions, dB/dq$^{2}$, are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ$^{±}$e$^{∓}$ decays and set 90% confidence-level upper limits on the branching fraction in the range of 10$^{-8}$ for B$^{+}$ → K$^{+}$μ$^{±}$e$^{∓}$, and B$^{0}$ → K$^{0}$μ$^{±}$e$^{∓}$ modes