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Register a new userA new method to measure the CP violating angle gamma using B^pm -> pi^pm pi^+ pi^- and B^pm -> K^pm pi^+ pi^- decays
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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.
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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.
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.
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.
The first amplitude analysis of the $B^pm to pi^pm K^+ K^-$ decay is reported based on a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of $pp$ collisions recorded in 2011 and 2012 with the LHCb detector. The data is found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from $pipi leftrightarrow KK$ $S$-wave rescattering. The dominant contributions in the $pi^pm K^mp$ and $K^{+}K^{-}$ systems are the nonresonant and the $B^pm to rho(1450)^{0}pi^{pm}$ amplitudes, respectively, with fit fractions around $30%$. For the rescattering contribution, a sizeable fit fraction is observed. This component has the largest $CP$ asymmetry reported to date for a single amplitude of $(-66 pm 4 pm 2)%$, where the first uncertainty is statistical and the second systematic. No significant $CP$ violation is observed in the other contributions.
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