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Register a new userThe CP violating asymmetry in $B^{pm} to M {bar M} pi^{pm}$ decays
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We analyze the asymmetry in the partial widths for the decays $B^{pm} to M {bar M} pi^{pm}$ ($ M = pi^+, K ^+, pi^0, eta$), which results from the interference of the nonresonant decay amplitude with the resonant amplitude for $B^{pm} to chi_{c0} pi^{pm} $ followed by the decay $chi_{c0} to M {bar M} $. The CP violating phase $gamma$ can be extracted from the measured asymmetry. We find that the partial width asymmetry for $B^pm to pi^+ pi^- pi^pm$ is about $0.33~sin gamma$, and about $0.45~ sin gamma$ for $B^pm to K^+ K^-pi^pm$, while it is somewhat smaller for $B^pm to pi^0 pi^0 pi^pm$ and $B^pm to eta eta pi^pm$. Potential sources of uncertainties in these results, primarily coming from poorly known input parameters, are discussed.
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A new and simple procedure to measure the angle $gamma$ from $B^{pm} to pi^{pm}pi^+pi^-$ and $B^{pm} to K^{pm}pi^+pi^-$ decays using SU(3) symmetry is presented. It is based on a full Dalitz plot analysis of these decays. All diagrams, including strong and electroweak penguins, are considered in the procedure. The method is also free from final state interaction problems. The theoretical error in the extraction of $gamma$ within the method should be of the order of $10^{rm o}$ or even less. Taking into account the B-meson production in the first generation of B factories and recent measurements from CLEO, this method could bring the best measurement of $gamma$ in the next years.
We analyze the partial rate asymmetry in $B^{pm} to P {bar P} pi^{pm}$ decays ($ P = pi^+, K ^+, pi^0, eta$) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for $B^{pm} to chi_{c0} pi^{pm} $ followed by the decay $chi_{c0} to P {bar P} $. The CP violating phase $gamma$ can be extracted from the measured asymmetry. We find that the partial rate asymmetry for $B^pm to pi^+ pi^- pi^pm$ is $0.33~sin gamma$, while for $B^pm to K^+ K^-pi^pm$ it amounts $0.45~ sin gamma$.
A model for the $B^pm to pi^-pi^+pi^pm$ decay amplitude is proposed to study the large CP violation observed at the high mass region of the Dalitz plane. A short distance $ b to u $ amplitude with the weak phase $gamma$ is considered together with the contribution of a hadronic charm loop and a s-wave $Dbar{D}to pipi$ rescattering. In the model, the $chi_c^0$ appears as a narrow resonant state of the $Dbar D$ system below threshold. It is introduced in an unitary two channel S-matrix model of the coupled $Dbar D$ and $pipi$ channels, where the $chi_c^0$ complex pole in $Dbar D$ channel shows its signature in the off-diagonal matrix element and in the associated $Dbar{D}to pipi$ transition amplitude. The strong phase of the resulting decay amplitude has a sharp sign change at the $Dbar D$ threshold, changing the sign of the CP asymmetry, as it is observed in the data. We conclude that the hadronic charm loop and rescattering mechanism are relevant to the broadening of the CP asymmetry around the $chi_c^0$ resonance in the $pipi$ channel. This novel mechanism provides a possible interpretation of the CP asymmetry defier experimental result presented by the LHCb collaboration for the $B^pm to pi^-pi^+pi^pm$ decay in the high mass region.
The $B^{pm}$ meson production asymmetry in $pp$ collisions is measured using $B^+ to bar{D}^0 pi^+$ decays. The data were recorded by the LHCb experiment during Run 1 of the LHC at centre-of-mass energies of $sqrt{s}=$ 7 and 8 TeV. The production asymmetries, integrated over transverse momenta in the range $2 < p_{rm T} < 30$ GeV/$c$, and rapidities in the range $2.1 < y < 4.5$, are measured to be begin{align*} mathcal{A}_{rm prod}(B^+,sqrt{s}=7~{rm TeV}) &= (-0.41 pm 0.49 pm 0.10) times 10^{-2}, mathcal{A}_{rm prod}(B^+,sqrt{s}=8~{rm TeV}) &= (-0.53 pm 0.31 pm 0.10) times 10^{-2}, end{align*} where the first uncertainties are statistical and the second are systematic. These production asymmetries are used to correct the raw asymmetries of $B^{+} to J/psi K^{+}$ decays, thus allowing a measurement of the $CP$ asymmetry, begin{equation*} mathcal{A}_{CP} = (0.09 pm 0.27 pm 0.07) times 10^{-2}. end{equation*}
Measurements of $CP$ observables in $B^pm rightarrow D^{(*)} K^pm$ and $B^pm rightarrow D^{(*)} pi^pm$ decays are presented, where $D^{(*)}$ indicates a neutral $D$ or $D^*$ meson that is an admixture of $D^{(*)0}$ and $bar{D}^{(*)0}$ states. Decays of the $D^*$ meson to the $Dpi^0$ and $Dgamma$ final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the $B$ candidate invariant mass distribution. Decays of the $D$ meson are fully reconstructed in the $K^pm pi^mp$, $K^+ K^-$ and $pi^+ pi^-$ final states. The analysis uses a sample of charged $B$ mesons produced in $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb$^{-1}$ taken at centre-of-mass energies of $sqrt{s}$ = 7, 8 and 13 TeV, respectively. The study of $B^{pm} to D^{*} K^{pm}$ and $B^{pm} to D^{*} pi^{pm}$ decays using a partial reconstruction method is the first of its kind, while the measurement of $B^{pm} to D K^{pm}$ and $B^{pm} to D pi^{pm}$ decays is an update of previous LHCb measurements. The $B^{pm} to D K^{pm}$ results are the most precise to date.
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