Search

We introduce an anomalous top quark coupling (right-handed current) into the standard model Lagrangian. Based on this, a more complete calculation of {ital b}{r_arrow}{ital s}{gamma} decay including leading log QCD corrections from {ital m}{sub {ital t}} to {ital M}{sub {ital W}} in addition to corrections from {ital M}{sub {ital W}} to {ital m}{sub {ital b}} is given. The inclusive decay rate is found to be suppressed compared with the case without QCD running from {ital m}{sub {ital t}} to {ital M}{sub {ital W}} except at the time of small values of {vert_bar}{ital f}{sub {ital R}}{sup {ital t}{ital b}}{vert_bar}. For example, when {ital f}{sub {ital R}}{sup {ital t}{ital b}}={minus}0.08, it is only 1/10 of the value given before. As {vert_bar}{ital f}{sub {ital R}}{sup {ital t}{ital b}}{vert_bar} gets smaller, this contribution is an enhancement as in the standard model case. From the new experiment of the CLEO Collaboration, strict restrictions to parameters of this top-bottom quark coupling are found.

In this work we use the heavy-quark-light-diquark picture to study the semileptonic decay {lambda}{sub b}{yields}{lambda}{sub c}+l+{nu}{sub l} in the so-called hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for larger q{sup 2} (corresponding to small recoil), which is the invariant mass square of l+{nu}, whereas the perturbative QCD approach for smaller q{sup 2} to calculate the form factors. The turning point where we require the form factors derived in the two approaches to be connected, is chosen near {rho}{sub cut}=1.1. It is noted that the kinematic parameter {rho} which is usually adopted in the perturbative QCD approach, is in fact exactly the same as the recoil factor {omega}=v{center_dot}v{sup '} used in HQET where v, v{sup '} are the four velocities of {lambda}{sub b} and {lambda}{sub c} respectively. We find that the final result is not very sensitive to the choice, so that it is relatively reliable. Moreover, we apply a proper numerical program within a small range around {rho}{sub cut} to make the connection sufficiently smooth and we parametrize the form factor by fitting the curve gained in the hybrid scheme. The expression and involved parameters can be compared with the ones gained by fitting the experimentalmore » data. In this scheme the end-point singularities do not appear at all. The calculated value is satisfactorily consistent with the data which is recently measured by the DELPHI collaboration within 2 standard deviations.« less

We study the rare decays B{sub s}{sup 0}{yields}D{sup {+-}}{pi}{sup {+-}} and B{sub s}{sup 0}{yields}D{sup {+-}}{pi}{sup {+-}}, which can occur only via annihilation type W exchange diagrams in the standard model. The time-dependent decay rates of the four channels can provide four CP parameters, which are experimentally measurable. We show that the Cabibbo-Kobayashi-Maskawa angle {phi}{sub 3}={gamma} can be determined from these parameters without any theoretical model dependence. These channels can be measured in future LHCb experiments to provide a clean way for {gamma} measurement.

The rare decays B-0 --> D-s(-) K+ and B+ --> D-s(+)(K) over bar (0) can occur only via annihilation type diagrams in the standard model. We calculate these decays in the perturbative QCD approach. We found that the calculated branching ratio of B-0 --> Ds-K+ agreed with the data which had been observed in the KEK and SLAC B factories. The decay B+ --> D-s(+)(K) over bar (0) has a very small branching ratio at O(10(-8)), due to the suppression from the CKM matrix elements \V-ub* V-cd\.

We calculate the branching ratios and $\mathrm{CP}$ asymmetries for ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}, {B}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0},$ and ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ decays, in a perturbative QCD approach. In this approach, we calculate nonfactorizable and annihilation type contributions, in addition to the usual factorizable contributions. We find that the annihilation diagram contributions are not very small as previously argued. Our result is in agreement with the measured branching ratio of $\stackrel{\ensuremath{\rightarrow}}{B}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ by the CLEO Collaboration. With a non-negligible contribution from annihilation diagrams and a large strong phase, we predict a large direct $\mathrm{CP}$ asymmetry in ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}},$ and ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0},$ which can be tested by the current running B factories.