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Register a new userMeasurement of $pi^0 Lambda$, $bar{K}^0 n$, and $pi^0 Sigma^0$ production in $K^- p$ interactions for $p_{K^-}$ between 514 and 750 MeV/$c$
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Differential cross sections and hyperon polarizations have been measured for $bar{K}^0 n$, $pi^0 Lambda$, and $pi^0 Sigma^0$ production in $K^- p$ interactions at eight $K^-$ momenta between 514 and 750 MeV/$c$. The experiment detected the multiphoton final states with the Crystal Ball spectrometer using a $K^-$ beam from the Alternating Gradient Synchrotron of BNL. The results provide significantly greater precision than the existing data, allowing a detailed reexamination of the excited hyperon states in our energy range.
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Differential cross sections for $K^-$ radiative capture in flight on the proton, leading to the $gammaLambda$ and $gammaSigma^0$ final states, have been measured at eight $K^-$ momenta between 514 and 750 MeV/$c$. The data were obtained with the Crystal Ball multiphoton spectrometer installed at the separated $K/pi$ beam line C6 of the BNL Alternating Gradient Synchrotron. The results substantially improve the existing experimental data available for studying radiative decays of excited hyperon states. An exploratory theoretical analysis is performed within the Regge-plus-resonance approach. According to this analysis, the $gammaSigma^0$ final state is dominated by hyperonresonance exchange and hints at an important role for a resonance in the mass region of 1700 MeV. In the $gammaLambda$ final state, on the other hand, the resonant contributions account for only half the strength, and the data suggest the importance of a resonance in the mass region of 1550 MeV.
A partial wave analysis of antiproton-proton annihilation data in flight at 900 $MeV/c$ into $pi^0 pi^0 eta$ , $pi^0 eta eta$ and $K^+ K^- pi^0$ is presented. The data were taken at LEAR by the Crystal Barrel experiment in 1996. The three channels have been coupled together with $pipi$-scattering isospin I=0 S- and D-wave as well as I=1 P-wave data utilizing the K-matrix approach. Analyticity is treated using Chew-Mandelstam functions. In the fit all ingredients of the K-matrix, including resonance masses and widths, were treated as free parameters. In spite of the large number of parameters, the fit results are in the ballpark of the values published by the Particle Data Group. In the channel $pi^0 pi^0 eta$ a significant contribution of the spin exotic $I^G=1^-$ $J^{PC}=1^{-+}$ $pi_1$-wave with a coupling to $pi^0 eta$ is observed. Furthermore the contributions of $phi(1020) pi^0$ and $K^*(892)^pm K^mp$ in the channel $K^+ K^- pi^0$ have been studied in detail. The differential production cross section for the two reactions and the spin-density-matrix elements for the $phi(1020)$ and $K^*(892)^pm$ have been extracted. No spin-alignment is observed for both vector mesons. The spin density matrix elements have been also determined for the spin exotic wave.
Using a data sample corresponding to 13.7 fb^-1 collected with the CLEO II and II.V detectors, we report new branching fraction measurements for two Cabibbo-suppressed decay modes of the D^+ meson: Br(D^+ to pi^+ pi^0) = (1.3 +/- 0.2) x 10^-3 and Br(D^+ to bar{K}^0 K^+) = (5.2 +/- 0.6) x 10^-3 which are significant improvements over past measurements. The errors include statistical and systematical uncertainties as well as the uncertainty in the absolute D^+ branching fraction scale. We also set the first 90% confidence level upper limit on the branching fraction of the doubly Cabibbo-suppressed decay mode Br(D^+ to K^+ pi^0) < 4.2 x 10^-4.
Using data samples collected with the BESIII detector at center-of-mass energies $sqrt{s} = 4.23, 4.26, 4.36,$ and $4.42$~rm{GeV}, we measure the branching fractions of $eta_cto K^+K^-pi^0$, $K^0_S K^{pm}pi^{mp}$, $2(pi^+pi^-pi^0)$, and $p bar{p}$, via the process $e^+e^-topi^+pi^-h_c$, $h_ctogammaeta_c$. The corresponding results are $(1.15pm0.12pm0.10)%$, $(2.60pm0.21pm0.20)%$, $(15.2pm1.8pm1.7)%$, and $(0.120pm0.026pm0.015)%$, respectively. Here the first uncertainties are statistical, and the second ones systematic. Additionally, the charged track multiplicity of $eta_c$ decays is measured for the first time.
Recently the branching ratios for $B^+to K^+bar K^0$ and $B^0 to K^0 bar K^0$ have been measured. Data indicate that the annihilation amplitudes in these decays are not zero. A non-zero annihilation amplitude plays an important role in CP violation for $B^+to pi^+ K^0, K^+ bar K^0$. Using the measured branching ratios for these decays, we show that there is an absolute bound of 5% for the size of CP asymmetry in $B^+to pi^+ K^0$ from a relation between the amplitudes of these decays. The size of CP asymmetry in $B^+ to K^+bar K^0$ can, however, be as large as 90%. Future experimental data will test these predictions.
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