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Register a new userMeasurement of $CP$ asymmetries and polarisation fractions in $B_s^0 rightarrow K^{*0}bar{K}{}^{*0}$ decays
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An angular analysis of the decay $B_s^0 rightarrow K^{*0}bar{K}{}^{*0}$ is performed using $pp$ collisions corresponding to an integrated luminosity of $1.0$ ${fb}^{-1}$ collected by the LHCb experiment at a centre-of-mass energy $sqrt{s} = 7$ TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction $f_L = 0.201 pm 0.057 {(stat.)} pm 0.040{(syst.)}$ for the $B_s^0 rightarrow K^*(892)^0 bar{K}{}^*(892)^0$ decay. A large scalar contribution from the $K^{*}_{0}(1430)$ and $K^{*}_{0}(800)$ resonances is found, allowing the determination of additional $CP$ asymmetries. Triple product and direct $CP$ asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction $mathcal{B}(B_s^0 rightarrow K^*(892)^0 bar{K}{}^*(892)^0)$ is measured to be $(10.8 pm 2.1 { rm (stat.)} pm 1.4 { rm (syst.)} pm 0.6 (f_d/f_s) ) times 10^{-6}$.
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The resonant substructure of $B_s^0 rightarrow bar{D}^0 K^- pi^+$ decays is studied with the Dalitz plot analysis technique. The study is based on a data sample corresponding to an integrated luminosity of $3.0,{rm fb}^{-1}$ of $pp$ collision data recorded by LHCb. A structure at $m(bar{D}^0 K^-) approx 2.86 {rm GeV}/c^2$ is found to be an admixture of spin-1 and spin-3 resonances. The masses and widths of these states and of the $D^*_{s2}(2573)^-$ meson are measured, as are the complex amplitudes and fit fractions for all the $bar{D}^0 K^-$ and $K^-pi^+$ components included in the amplitude model. In addition, the $D^*_{s2}(2573)^-$ resonance is confirmed to be spin-2.
We report measurements of CP violation parameters in $B^0 to K^0 pi^0$ decays based on a data sample of $657 times 10^6 Bbar{B}$ pairs collected with the Belle detector at the KEKB $e^+ e^-$ asymmetric-energy collider. We use $B^0 to K^0_S pi^0$ decays for both mixing-induced and direct $CP$ violating asymmetry measurements and $B^0 to K^0_L pi^0$ decays for the direct CP violation measurement. The CP violation parameters obtained are $sin 2 phi_1^{rm eff} = +0.67 pm 0.31{(stat)} pm 0.08 {(syst)}$ and $mathcal{A}_{K^0 pi^0} = +0.14 pm 0.13{(stat)} pm 0.06 {(syst)}$. The branching fraction of $B^0 to K^0 pi^0$ decay is measured to be $mathcal{B}(B^0 to K^0 pi^0) = (8.7pm0.5 (rm{stat.})pm0.6 (rm{syst.}))times 10^{-6}$. The observed $mathcal{A}_{K^0 pi^0}$ value differs by 1.9 standard deviations from the value expected from an isospin sum rule.
Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^- K^+$ and $pi^- pi^+$ are measured using proton-proton collisions corresponding to $3mathrm{,fb}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7mathrm{,Tekern -0.1em V}$ and $8mathrm{,Tekern -0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be begin{align} Delta A_{CP} = A_{CP}(K^-K^+)-A_{CP}(pi^-pi^+) = (+0.14 pm 0.16mathrm{,(stat)} pm 0.08mathrm{,(syst)})% . onumber end{align} A measurement of $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be begin{align} A_{CP}(K^-K^+) = (-0.06 pm 0.15mathrm{,(stat)} pm 0.10mathrm{,(syst)}) % , onumber end{align} where the correlation coefficient between $Delta A_{CP}$ and $A_{CP}(K^-K^+)$ is $rho=0.28$. By combining these results, the $CP$ asymmetry in the $D^0rightarrowpi^-pi^+$ channel is $A_{CP}(pi^-pi^+)=(-0.20pm0.19mathrm{,(stat)}pm0.10mathrm{,(syst)})%$.
A search for CP violation in $D^0 rightarrow K^{-} K^{+} $ and $D^0 rightarrow pi^{-} pi^{+} $ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of $3~fb^{-1}$, collected using the LHCb detector at centre-of-mass energies of 7 and $8~$TeV. The flavour of the charm meson is inferred from the charge of the pion in $D^{*+}rightarrow D^0pi^+$ and $D^{*-}rightarrow bar{D^0}pi^{-}$ decays. The difference between the CP asymmetries in $D^0 rightarrow K^{-} K^{+} $ and $D^0 rightarrow pi^{-} pi^{+} $ decays, $Delta A_{CP} equiv A_{CP}(K^{-} K^{+}) - A_{CP}(pi^{-} pi^{+})$, is measured to be $left( -0.10 pm 0.08(stat) pm 0.03(syst) right) %$. This is the most precise measurement of a time-integrated CP asymmetry in the charm sector from a single experiment.
We report measurements of the branching fractions and $CP$ asymmetries for $D_s^{+} rightarrow K^{+} eta $, $D_s^{+} rightarrow K^{+} pi^0 $, and $D_s^{+} rightarrow pi^{+} eta $ decays, and the branching fraction for $D_s^{+} rightarrow pi^{+} pi^0$. Our results are based on a data sample corresponding to an integrated luminosity of 921 fb$^{-1}$ collected by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. Our measurements of $CP$ asymmetries in these decays are the most precise to-date; no evidence for $CP$ violation is found.
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