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Proceedings of the CKM 2005 Workshop (WG5), UC San Diego, 15-18 March 2005.
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We give a summary of the discussions in Working Group V of the CKM2010 workshop dealing with determinations of the angle gamma of the unitarity triangle of the Cabibbo-Kobayashi-Maskawa matrix from B-meson decays into charmed final states.
We investigate the possibility that scalar leptoquarks generate consequential effects on the flavor-changing neutral-current decays of charmed hadrons into final states with missing energy ($ ot!!E$) carried away by either standard model or sterile neutrinos. We focus on scenarios involving the $R_2$, $tilde R_2$, and $bar S_1$ leptoquarks and take into account various pertinent constraints, learning that meson-mixing ones and those inferred from collider searches can be of significance. We find in particular that the branching fractions of charmed meson decays $Dto M! ot!!E$, $M=pi,rho$, and $D_sto K^{(*)}! ot!!E$ and singly charmed baryon decays $Lambda_c^+to p! ot!!E$ and $Xi_ctoSigma! ot!!E$ are presently allowed to attain the $10^{-7}$-$10^{-6}$ levels if induced by $R_2$ and that the impact of $tilde R_2$ is comparatively much less. In contrast, the contributions of $bar S_1$, which couples to right-handed up-type quarks and the sterile neutrinos, could lead to branching fractions as high as order $10^{-3}$. This suggests that these charmed hadron decays might be within reach of the BESIII and Belle II experiments or future super charm-tau factories and could serve as potentially promising probes of leptoquark interactions with sterile neutrinos.
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.
To date, the weak-phase $gamma$ has been measured using two-body $B$-meson decays such as $Bto D K$ and $Bto Dpi$, whose amplitudes contain only tree-level diagrams. But $gamma$ can also be extracted from three-body charmless hadronic $B$ decays. Since the amplitudes for such decays contain both tree- and loop-level diagrams, $gamma$ obtained in this way is sensitive to new physics that can enter into these loops. The comparison of the values of $gamma$ extracted using tree-level and loop-level methods is therefore an excellent test for new physics. In this talk, we will show how U-spin and flavor-SU(3) symmetries can be used to develop methods for extracting $gamma$ from $Bto Kpipi$ and $Bto KK{bar K}$ decays. We describe a successful implementation of the flavor-SU(3) symmetry method applied to BaBar data.
We study the exclusive semileptonic $B$-meson decays $Bto K(pi)ell^+ell^-$, $Bto K(pi) ubar u$, and $Btopitau u$, computing observables in the Standard model using the recent lattice-QCD results for the underlying form factors from the Fermilab Lattice and MILC Collaborations. These processes provide theoretically clean windows into physics beyond the Standard Model because the hadronic uncertainties are now under good control for suitably binned observables. For example, the resulting partially integrated branching fractions for $Btopimu^+mu^-$ and $Bto Kmu^+mu^-$ outside the charmonium resonance region are 1-2$sigma$ higher than the LHCb Collaborations recent measurements, where the theoretical and experimental errors are commensurate. The combined tension is 1.7$sigma$. Combining the Standard-Model rates with LHCbs measurements yields values for the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_{td}|=7.45{(69)}times10^{-3}$, $|V_{ts}|=35.7(1.5)times10^{-3}$, and $|V_{td}/V_{ts}|=0.201{(20)}$, which are compatible with the values obtained from neutral $B_{(s)}$-meson oscillations and have competitive uncertainties. Alternatively, taking the CKM matrix elements from unitarity, we constrain new-physics contributions at the electroweak scale. The constraints on the Wilson coefficients ${rm Re}(C_9)$ and ${rm Re}(C_{10})$ from $Btopimu^+mu^-$ and $Bto Kmu^+mu^-$ are competitive with those from $Bto K^* mu^+mu^-$, and display a 2.0$sigma$ tension with the Standard Model. Our predictions for $Bto K(pi) ubar u$ and $Btopitau u$ are close to the current experimental limits.
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