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Register a new userLight mesons and charm decays: New results from E791
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Carla Gobel
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We will discuss how the decays of charm mesons can be used to study light mesons spectroscopy, by presenting recent results of Dalitz plot analyses using data from Fermilab experiment E791. Emphasis will be on scalar mesons, which are found to have large contribution to the $D$ decays studied. In addition to the usual extraction of decay fractions and relative phases of the intermediate amplitudes, the Dalitz plot technique is used to measure masses and widths of scalar resonances. From the $D_s$ decay, we obtain masses and widths of $f_0(980)$ and $f_0(1370)$. We find evidence for a light and broad scalar resonance, the $sigma$ meson, in $D^+topi^-pi^+pi^+$ decay. Preliminary studies also show evidence for a light and broad resonance, the $kappa$ meson, in $D^+to K^-pi^+pi^+$ decay. These results illustrate the potential of charm decays as a laboratory for the study of light mesons.
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We present recent results on light mesons based on Dalitz plot analyses of charm decays from Fermilab experiment E791. Scalar mesons are found to have large contributions to the decays studied, $D^+to K^-pi^+pi^+$ and $D^+, D_s^+topi^-pi^+pi^+$. From the $Kpipi$ final state, we find good evidence for the existence of the light and broad $kappa$ meson and we measure its mass and width. We also discuss recently published results on the 3$pi$ final states, especially the measurement of the $f_0$ parameters and the evidence for the $sigma$ meson from $D^+tosigmapi^+$. These results demonstrate the importance of charm decays as a new environment for the study of light meson physics.
We present the measurements, performed by the Belle II experiment, related to the B and D meson decays. These results are based on 63 fb$^{-1}$ and 9 fb$^{-1}$ of $e^+e^-$ collision data recorded by the Belle II detector at a center-of-mass energy corresponding to the mass of the Y(4S) resonance and 60 MeV below the Y(4S) resonance. The results reassure that Belle II is in the right direction in pursuit of measuring the Standard Model predictions with improved precision.
The phenomenon of mixing in neutral meson systems has now been observed in all flavours, but only in the past year in the D0 system. The standard model anticipated that, for the charm sector, the mixing rate would be small, and also that CP violation, either in mixing or in direct decay, would be below the present levels of observability. It is hoped that further study of these phenomena might reveal signs of new physics. A review of recently available, experimental results is given.
A search for decays of $B_c^+$ mesons to two charm mesons is performed for the first time using data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The decays considered are $B_c^+to D^{(*)+}_{(s)} overline{D}^{(*)0}$ and $B_c^+to D^{(*)+}_{(s)} D^{(*)0}$, which are normalised to high-yield $B^+to D^+_{(s)} overline{D}^0$ decays. No evidence for a signal is found and limits are set on twelve $B_c^+$ decay modes.
A data set corresponding to an integrated luminosity of $9 text{fb}^{-1}$ of proton-proton collisions collected by the LHCb experiment has been analysed to search for $B_c^+ to D^{(*)+}_{(s)} overset{scriptstyle (-)}{D}{}^{(*)0}$ decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to $B^+$ decays to final states with similar topologies, are obtained for fourteen $B_c^+$ decay modes. For the decay $B_c^+ to D_s^+ {overline{D}}^0$, an excess with a significance of 3.4 standard deviations is found.
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