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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.
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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.
A search for the decays of the $B_c^+$ meson to $pbar ppi^+$ is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 $mathrm{fb}^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of $7$ and $8$ TeV. No signal is found and an upper limit, at 95% confidence level, is set, $frac{f_c}{f_u}timesmathcal{B}(B_c^+to pbar ppi^+)<3.6times10^{-8}$ in the kinematic region $m(pbar p)<2.85mathrm{,Gekern -0.1em V!/}c^2$, $p_{rm T}(B)<20mathrm{,Gekern -0.1em V!/}c$ and $2.0<y(B)<4.5$, where $mathcal{B}$ is the branching fraction and $f_c$ ($f_u$) is the fragmentation fraction of the $b$ quark into a $B_c^+$ ($B^+$) meson.
Using data collected near the Ds*+ Ds- peak production energy Ecm = 4170 MeV by the CLEO-c detector, we study the decays of Ds+ mesons to two pseudoscalar mesons. We report on searches for the singly-Cabibbo-suppressed Ds+ decay modes K+ eta, K+ eta, pi+ K0S, K+ pi0, and the isospin-forbidden decay mode Ds+ to pi+ pi0. We normalize with respect to the Cabibbo-favored Ds+ modes pi+ eta, pi+ eta, and K+ K0S, and obtain ratios of branching fractions: Ds+ to K+ eta / Ds+ to pi+ eta = (8.9 +- 1.5 +- 0.4)%, Ds+ to K+ eta / Ds+ to pi+ eta = (4.2 +- 1.3 +- 0.3)%, Ds+ to pi+ K0S / Ds+ to K+ K0S = (8.2 +- 0.9 +- 0.2)%, Ds+ to K+ pi0 / Ds+ to K+ K0S = (5.0 +- 1.2 +- 0.6)%, and Ds+ to pi+ pi0 / Ds+ to K+ K0S < 4.1% at 90% CL, where the uncertainties are statistical and systematic, respectively.
We have searched for flavor-changing neutral current decays and lepton-number-violating decays of D^+ and D^+_s mesons to final states of the form h^+- e^-+ e^+, where h is either pi or K. We use the complete samples of CLEO-c open-charm data, corresponding to integrated luminosities of 818 pb^-1 at the center-of-mass energy E_CM = 3.774 GeV containing 2.4 x 10^6 D^+D^- pairs and 602 pb^-1 at E_CM = 4.170 GeV containing 0.6 x 10^6 D^*+-_s D^-+_s pairs. No signal is observed in any channel, and we obtain 90% confidence level upper limits on branching fractions B(D^+ --> pi^+ e^+ e^-) < 5.9 x 10^-6, B(D^+ --> pi^- e^+ e^+) < 1.1 x 10^-6, B(D^+ --> K^+ e^+ e^-) < 3.0 x 10^-6, B(D^+ --> K^- e^+ e^+) < 3.5 x 10^-6, B(D^+_s --> pi^+ e^+ e^-) < 2.2 x 10^-5, B(D^+_s --> pi^- e^+ e^+) < 1.8 x 10^-5, B(D^+_s --> K^+ e^+ e^-) < 5.2 x 10^-5, and B(D^+_s --> K^- e^+ e^+) < 1.7 x 10^-5.
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.
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