Covariant Light-Front Approach for B to K* gamma, K_1 gamma, K*_2 gamma Decays

Exclusive radiative B decays, B to K* gamma, K_1(1270) gamma, K_1(1400) gamma and K*_2(1430) gamma, are studied in the framework of a covariant light-front quark model. The tensor form factor T_1(q^2) at q^2=0, which is relevant to the decay B to K* gamma, is found to be 0.24, substantially smaller than what expected from the conventional light-front model or light-cone sum rules. Taking into account the sizable next-to-leading order (NLO) corrections, the calculated branching ratio of B to K* gamma agrees with experiment, while most of the existing models predict too large B to K* gamma compared to the data. The relative strength of B to K_1(1270) gamma and B to K_1(1400) gamma rates is very sensitive to the sign of the K_1(1270)-K_1(1400) mixing angle. Contrary to the other models in which K_1(1270) gamma and K_1(1400) gamma rates are predicted to be comparable, it is found that one of them is strongly suppressed owing to a large cancellation between two different form factor terms. The calculated branching ratio of B to K*_2 gamma is in a good agreement with experiment and this may imply the smallness of NLO corrections to this radiative decay mode.Comment: 18 pages, 2 figures; to be published in Phys. Rev.

Bottom Baryon Decays to Pseudoscalar Meson and Pentaquark

Based on SU(3) flavor symmetry, we decompose the decay amplitudes of bottom baryon decays to a pseudoscalar meson and an octet (a decuplet) pentaquark in terms of three (two) invariant amplitudes $T_1$ and $T_{2,3}$ ($\tilde T_1$ and $\tilde T_2$) corresponding to external $W$-emission and internal $W$-emission diagrams, respectively. For antitriplet bottom baryons $\Lambda_b^0,\Xi_b^0$ and $\Xi_b^-$, their decays to a decuplet pentaquark proceed only through the internal $W$-emission diagram. Assuming the dominance from the external $W$-emission amplitudes, we present an estimate of the decay rates relative to $\Lambda_b^0\to P_p^+K^-$, where $P_p^+$ is the hidden-charm pentaquark with the same light quark content as the proton. Hence, our numerical results will provide a very useful guideline to the experimental search for pentaquarks in bottom baryon decays. For example, $\Xi_b^0\to P_{\Sigma^+}K^-$, $\Xi_b^-\to P_{\Sigma^-}\bar K^0$, $\Omega_b^-\to P_{\Xi^-}\bar K^0$ and $\Omega_b^-\to P_{\Xi^0}K^-$ may have rates comparable to that of $\Lambda_b^0\to P_p^+K^-$ and these modes should be given the higher priority in the experimental searches for pentaquarks.Comment: 15 pages, 1 figure; references added, typos correcte

B to V, A, T Tensor Form Factors in the Covariant Light-Front Approach: Implications on Radiative B Decays

We reanalyze the $B\to M$ tensor form factors in a covariant light-front quark model, where $M$ represents a vector meson $V$, an axial-vector meson $A$, or a tensor meson $T$. The treatment of masses and mixing angles in the $K_{1A,1B}$ systems is improved, where $K_{1A}$ and $K_{1B}$ are the $^3P_1$ and $^1P_1$ states of the axial-vector meson $K_1$, respectively. Rates of $B\to M\gamma$ decays are then calculated using the QCD factorization approach. The updated $B\to K^*\gamma$, $B\to K_1(1270)\gamma$, $K_1(1400)\gamma$ and $K_2\gamma$ rates agree with the data. The $K_1(1270)$--$K_1(1400)$ mixing angle is found to be about $51^\circ$. The sign of the mixing angle is fixed by the observed relative strength of $B\to K_1(1270)\gamma$ and $K_1(1400)\gamma$. The formalism is then applied to $B_s\to M$ tensor form factors. We find that the calculated $B_s\to \phi\gamma$ rate is consistent with experiment, though in the lower end of the data. The branching fractions of $B_s\to f_1(1420)\gamma$ and $f'_2(1525)\gamma$ are predicted to be of order $10^{-5}$ and it will be interesting to search for these modes. Rates on $B_s\to f_1(1285)\gamma$, $h_1(1380)\gamma$, $h_1(1170)\gamma$, $f_2(1270)\gamma$ decays are also predicted.Comment: 26 pages, 3 figures, version to appear in PR

Strong Decays of Charmed Baryons in Heavy Hadron Chiral Perturbation Theory

Strong decays of charmed baryons are analyzed in the framework of heavy hadron chiral perturbation theory (HHChPT) in which heavy quark symmetry and chiral symmetry are synthesized. HHChPT works excellently for describing the strong decays of s-wave charmed baryons. For L=1 orbitally excited states, two of the unknown couplings, namely, $h_2$ and $h_{10}$, are determined from the resonant $\Lambda_c^+\pi\pi$ mode produced in the $\Lambda_c(2593)$ decay and the width of $\Sigma_c(2800)$, respectively. Predictions for the strong decays of the p-wave charmed baryon states $\Lambda_c(2625)$, $\Xi_c(2790)$ and $\Xi_c(2815)$ are presented. Since the decay $\Lambda_c(2593)^+\to\Lambda_c^+\pi\pi$ receives non-resonant contributions, our value for $h_2$ is smaller than the previous estimates. We also discuss the first positive-parity excited charmed baryons. We conjecture that the charmed baryon $\Lambda_c(2880)$ with $J^P=\frac52^+$ is an admixture of $\Lambda_{c2}(\frac52^+)$ with and $\tilde\Lambda''_{c3}(\frac52^+)$; both are L=2 orbitally excited states. The potential model suggests $J^P=\frac52^-$ or $\frac32^+$ for $\Lambda_c(2940)^+$. Measurements of the ratio of $\Sigma_c^*\pi/\Sigma_c\pi$ will enable us to discriminate the $J^P$ assignments for $\Lambda_c(2940)$. We advocate that the $J^P$ quantum numbers of $\Xi_c(2980)$ and $\Xi_c(3077)$ are $\frac12^+$ and $\frac52^+$, respectively. Under this $J^P$ assignment, it is ready to understand why $\Xi_c(2980)$ is broader than $\Xi_c(3077)$.Comment: 22 pages, the coupling g_2 is slightly modified, Tables 5 and 6 are updated; version to appear in PR

Resolving B-CP Puzzles in QCD Factorization

Within the framework of QCD factorization (QCDF), power corrections due to penguin annihilation can account for the observed rates of penguin-dominated two-body decays of $B$ mesons and direct CP asymmetries $A_{CP}(K^-\pi^+)$, $A_{CP}(K^{*-}\pi^+)$, $A_{CP}(K^-\rho^0)$ and $A_{CP}(\pi^+\pi^-)$. However, the predicted direct CP-violating effects in QCDF for $B^-\to K^-\pi^0,K^-\eta,\pi^-\eta$ and $\bar B^0\to\pi^0\pi^0$ are wrong in signs when confronted with experiment. We show that subleading $1/m_b$ power corrections to the color-suppressed tree amplitude due to spectator scattering or final-state interactions will yield correct signs for aforementioned CP asymmetries and accommodate the observed $\pi^0\pi^0$ and $\rho^0\pi^0$ rates simultaneously. Implications are discussed.Comment: 12 pages, 1 figure. Experimental data and references updated, to appear in PR

QCD Factorization for Charmless Hadronic B_s Decays Revisited

Branching fractions and CP-violating asymmetries of charmless $\bar B_s\to PP, VP, VV$ decays (P and V denoting pseudoscalar and vector mesons, respectively) are re-examined in the framework of QCD factorization (QCDF). We take into account subleading power corrections to the penguin annihilation topology and to color-suppressed tree amplitudes that are crucial for resolving the CP puzzles and rate deficit problems with penguin-dominated two-body decays and color-suppressed tree-dominated $\pi^0\pi^0$ and $\rho^0\pi^0$ modes in the $B_{u,d}$ sector. Many of the $B_s\to h_1h_2$ decays can be related to $B_d\to h_1h_2$ ones via U-spin or SU(3) symmetry. Some useful model-independent relations can be derived and tested. Mixing-induced CP asymmetries for many of the penguin-dominated decays are predicted to be very small in the standard model. They are sensitive to New Physics and offer rich possibilities of new discoveries. Measurements of direct CP-violating asymmetries can be used to discriminate QCDF from other competing approaches such as pQCD and soft-collinear effective theory.Comment: 38 page

Branching Fractions and Direct CP Violation in Charmless Three-body Decays of B Mesons

Charmless three-body decays of B mesons is studied using a simple model based on the framework of the factorization approach. Hadronic three-body decays receive both resonant and nonresonant contributions. Dominant nonresonant contributions to tree-dominated three-body decays arise from the $b\to u$ tree transition which can be evaluated using heavy meson chiral perturbation theory valid in the soft meson limit. For penguin-dominated decays, nonresonant signals come mainly from the penguin amplitude governed by the matrix elements of scalar densities . We use the measurements of $\bar B^0\to K_SK_SK_S$ to constrain the nonresonant component of $$. The intermediate vector meson contributions to three-body decays are identified through the vector current, while the scalar meson resonances are mainly associated with the scalar density. While the calculated direct CP violation in $B^-\to K^+K^-K^-$ and $B^-\to \pi^+\pi^-\pi^-$ decays agrees well with experiment in both magnitude and sign, the predicted CP asymmetries in $B^-\to \pi^- K^+K^-$ and $B^-\to K^-\pi^+\pi^-$ are wrong in signs when confronted with experiment. It has been conjectured recently that a possible resolution to this CP puzzle may rely on final-state rescattering of $\pi^+\pi^-$ and $K^+K^-$. Assuming a large strong phase associated with the matrix element arising from some sort of power corrections, we fit it to the data of $K^-\pi^+\pi^-$ and find a correct sign for $\pi^- K^+K^-$.Comment: 38 pages, Tables III-XI are revised, to appear in Phys. Rev.

Charmless Three-body Decays of B_s Mesons

Branching fractions and CP-violating asymmetries of charmless $B_s\to PPP$ decays with $P=K,\pi$ are studied using a simple model based on the factorization approach. The penguin-dominated modes $B_s\to \bar K^0 K^+\pi^-$ and $K^0K^-\pi^+$ have the largest rates among the three-body $B_s$ decays and they are dominated by the $K_0^*(1430)$ resonances and nonresonant contributions. The branching fraction of $B_s\to K^0K^+K^-$ is predicted to be $1.4\times 10^{-6}$, which is close to the high end of the measured result $(0.2-3.4)\times 10^{-6}$ obtained by LHCb. We find sizable CP violation in $K^0\pi^+\pi^-$, $K^0\pi^0\pi^0$, $K^0K^+K^-$ and $K_SK_SK_S$ channels. Just as the $B_u$ sector, the correlation of CP asymmetries $A_{CP}(B_s\to K^0\pi^+\pi^-)\approx -A_{CP}(B_s\to K^0K^+K^-)$ holds in $B_s$ decays. Several model-independent relations based on $U$-spin symmetry for CP asymmetries are derived. Although they cannot be tested by the present available data, they can be checked by the dynamical calculations. Since the $U$-spin symmetry which relates various matrix elements of scalar densities, for example, $<K^0K|\bar dq|0>$ and $$, is badly broken, the derived $U$-spin relations are generally not well respected.Comment: 15 pages, two figures; Tables I-III and Figs. 1-2 are updated; a new U-spin symmetry relation is added to Eq. (3.6); PRD versio

Strong Decays of Charmed Baryons in Heavy Hadron Chiral Perturbation Theory: An Update

We first give a brief overview of the charmed baryon spectroscopy and discuss their possible structure and spin-parity assignments in the quark model. With the new Belle measurement of the widths of $\Sigma_c(2455)$ and $\Sigma_c(2520)$ and the recent CDF measurement of the strong decays of $\Lambda_c(2595)$ and $\Lambda_c(2625)$, we give updated coupling constants in heavy hadron chiral perturbation theory. We find $g_2=0.565^{+0.011}_{-0.024}$ for $P$-wave transitions between $s$-wave and $s$-wave baryons, and $h_2$, one of the couplings responsible for $S$-wave transitions between $s$-wave and $p$-wave baryons, is extracted from $\Lambda_c(2595)^+\to\Lambda_c^+\pi\pi$ to be $0.63\pm0.07$. It is substantially enhanced compared to the old value of order 0.437. With the help from the quark model, two of the couplings $h_{10}$ and $h_{11}$ responsible for $D$-wave transitions between $s$-wave and $p$-wave baryons are determined from $\Sigma_c(2880)$ decays. There is a tension for the coupling $h_2$ as its value extracted from $\Lambda_c(2595)^+\to \Lambda_c^+\pi\pi$ will imply $\Xi_c(2790)^0\to\Xi'_c\pi$ and $\Xi_c(2815)^+\to\Xi_c^*\pi$ rates slightly above the current limits. It is conceivable that SU(3) flavor symmetry breaking can help account for the discrepancy.Comment: 18 pages, 1 figure. References added, to appear in Phys. Rev. D. arXiv admin note: text overlap with arXiv:1508.07233, arXiv:hep-ph/061028

Production of P-wave Charmed Mesons in Hadronic B Decays

Production of even-parity charmed mesons in hadronic B decays is studied. Specifically, we focus on the Cabibbo-allowed decays $\bar B\to D^{**}\pi$ and $\bar D^{**}_sD^{(*)}$, where $D^{**}$ denotes generically a p-wave charmed meson. While the measured color-allowed decays $\bar B^0\to D^{**+}\pi^-$ are consistent with the theoretical expectation, the experimental observation of $B^-\to D^{**0}\pi^-$ for the broad $D^{**}$ states is astonishing as it requires that the color-suppressed contribution dominates over the color-allowed one, even though the former is $1/m_b$ suppressed in the heavy quark limit. In order to accommodate the data of $\bar B\to D^{**}\pi^-$, it is found that $a_2/a_1\approx -0.5$ with a sign opposite to that in $\bar B\to D\pi$ decays, where $a_1$ and $a_2$ are the effective Wilson coefficients for color-allowed and color-suppressed decay amplitudes, respectively. The decay constants and form factors for $D^{**}$ and the Isgur-Wise functions $\tau_{1/2}(\omega)$ and $\tau_{3/2}(\omega)$ are extracted from the data of $B\to D^{**}\pi$ decays. The Isgur-Wise functions calculated in the covariant light-front quark model are in good agreement with experiment. The neutral modes $\bar B^0\to D^{**0}\pi^0$ for $D^{**}=D^*_0(2400),D'_1(2430)$ and $\bar B^0\to D'^0_1(2430)\omega$ are predicted to have branching ratios of order $10^{-4}$ which are also supported by isospin argument. The decay constants of $D_{s0}^*(2317)$ and $D'_{s1}(2460)$ are inferred from the measurements of $\bar B\to D_s^{**-}D$ to be $58\sim 86$ MeV and $130\sim 200$ MeV, respectively. Contrary to the decay constants $f_{D_0^*}$ and $f_{D'_1}$ which are similar in size, the large disparity between $f_{D_{s0}^*}$ and $f_{D'_{s1}}$ is surprising and unexpected.Comment: 27 pages; Sec. IV is updated using the absolute branching ratios of B to D_{s1}(2460)D decays obtained by BaBa