Charmless hadronic B decays involving scalar mesons: Implications to the nature of light scalar mesons

The hadronic charmless B decays into a scalar meson and a pseudoscalar meson are studied within the framework of QCD factorization. Although the light scalar mesons $f_0(980)$ and $a_0(980)$ are widely perceived as primarily the four-quark bound states, in practice it is difficult to make quantitative predictions based on the four-quark picture for light scalars. Hence, predictions are made in the 2-quark model for the scalar mesons. Based on the QCD sum rule method, we have derived the leading-twist light-cone distribution amplitudes of scalar mesons and their decay constants. The short-distance approach suffices to explain the observed large rates of $f_0(980)K^-$ and $f_0(980)\bar K^0$ that receive major penguin contributions from the $b\to ss\bar s$ process. When $f_0(980)$ is assigned as a four-quark bound state, there exist extra diagrams contributing to $B\to f_0(980)K$. Therefore, a priori the $f_0(980)K$ rate is not necessarily suppressed for a four-quark state $f_0(980)$. The calculated $\bar B^0\to a_0^+(980)\pi^-$ and $a_0^+(980)K^-$ rates exceed slightly the current experimental limits. If the branching ratio of $\bar B^0\to a_0^+(1450)\pi^-$ is measured at the level of $(4\sim 6)\times 10^{-6}$ while $a_0^+(980)\pi^-$ is found to be smaller, say, of order $(1\sim 2)\times 10^{-6}$ or even smaller than this, it will be likely to imply a 2-quark nature for $a_0(1450)$ and a four-quark assignment for $a_0(980)$. The penguin-dominated modes $a_0(980)K$ and $a_0(1450)K$ receive dominant weak annihilation contributions.Comment: 42 pages and 5 figures. Form factors for B to excited scalar mesons are calculated, signs are flipped for the decay constants of excited states (Appendix B), Tables 5 to 9 are revised. Version to appear in PR

Raspadi B → f0(980) K u QCD faktorizaciji

The decay B → f0(980)K is studied within the framework of QCD factorization. Its decay rate is suppressed relative to B → π 0K owing to a destructive interference between (S − P)(S + P) and (V − A)(V − A) penguin contributions. The interference between the (S − P)(S + P) penguin contributions arising from the strange and light quark components of f0(980) is destructive for π/2 > θ > 0 and constructive for −π/2 π0K+ and f0(980)K0 >∼ π 0K0 decay rates. Possible mechanisms for the enhancement of f0(980)K are discussed.Proučava se raspad B → f0(980) K u okviru QCD faktorizacije. Vjerojatnost raspada je potisnuta u odnosu na B → π 0 K raspad zbog destruktivne interferencije pingvinskih doprinosa (S – P)(S + P) i (V – A)(V – A). Interferencija pingvinskih doprinosa (S – P)(S + P), koja nastaje zbog komponenata stranog i laganog kvarka u f0(980), je destruktivna za π/2 > θ > 0 i konstruktivna za −π/2 π0 K+ i f0(980)K0 >∼ π 0K0 . Raspravljaju se mogući mehanizmi povećane vjerojatnosti f0(980)K

Penguin-induced Radiative Baryonic B Decays Revisited

Weak radiative baryonic B decays $\bar B\to B_1\bar B_2\gamma$ mediated by the electromagnetic penguin process $b\to s\gamma$ are re-examined within the framework of the pole model. The meson pole contribution that has been neglected before is taken into account in this work. It is found that the intermediate $K^*$ contribution dominates in the $\Sigma\bar p\gamma$ mode and is comparable to the baryon pole effect in $\Lambda\bar p\gamma$ and $\Xi\bar\Lambda\gamma$ modes. The branching ratios for $B^-\to\Lambda\bar p\gamma$ and $B^-\to\Xi^0\bar\Sigma^-\gamma$ are of order $2.6\times 10^{-6}$ and $6\times 10^{-7}$, respectively. The threshold enhancement effect in the dibaryon mass spectrum is responsible by the meson pole diagram. We also study the angular distribution of the baryon in the dibaryon rest frame. The baryon pole diagrams imply that the antibaryon tends to emerge in the direction of the photon in the baryon-pair rest frame. The predicted angular asymmetry agrees with experiment for $B^-\to\Lambda\bar p\gamma$. Measurements of the correlation of the photon with the baryon allow us to discriminate between different models for describing the radiative baryonic B decays. For decays $B\to\Xi\bar\Sigma\gamma$, a large correlation of the photon to the $\bar\Sigma$ and a broad bump in the dibaryon mass spectrum are predicted.Comment: 10 pages, 4 figure

Penguin-Induced Radiative Baryonic B Decays

Weak radiative baryonic B decays B\to\B_1\ov \B_2\gamma mediated by the electromagnetic penguin process $b\to s\gamma$ have appreciable rates larger than their two-body counterparts B\to\B_1\ov \B_2. The branching ratios for $B^-\to\Lambda\bar p\gamma$ and $B^-\to\Xi^0\bar\Sigma^-\gamma$ are sizable, falling into the range of $(1\sim 6)\times 10^{-6}$ with the value preferred to be on the large side, and not far from the bottom baryon radiative decays $\Lambda_b\to\Lambda\gamma$ and $\Xi_b\to\Xi\gamma$ due to the large short-distance enhancement for $b\to s\gamma$ penguin transition and the large strong coupling of the anti-triplet bottom baryons with the B meson and the light baryon. These penguin-induced radiative baryonic B decay modes should be accessible by B factories.Comment: 8 pages, 1 figure. Branching ratios are corrected as previous values are too large by a factor of 2 and a new reference is adde