arXiv subjects

Hsiang-nan Li

Publications and source records attributed to Hsiang-nan Li.

At least 109 records · Page 6Linked to original sources

arXiv2008

Okubo-Zweig-Iizuka-rule violation and B\to η^{(\prime)}K branching ratios

We show that few-percent Okubo-Zweig-Iizuka-rule violating effects in the quark-flavor basis for the $η$-$η'$ mixing can enhance the chiral scale associated with the $η_q$ meson few times. This enhancement is sufficient for accommodating the dramatically different data of the $B\toη^{\prime} K$ and $B\toηK$ branching ratios. We comment on other proposals for resolving this problem, including flavor-singlet contributions, axial U(1) anomaly, and nonperturbative charming penguins. Discrimination of the above proposals by means of the $B\toη^{(\prime)}\ellν$ and $B_s\toη^{(\prime)}\ell\ell$ data is suggested.

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arXiv2007

Possible complex annihilation and B -> K pi direct CP asymmetry

We point out that a sizable strong phase could be generated from the penguin annihilation in the soft-collinear effective theory for B meson decays. Keeping a small scale suppressed by O(Lambda/m_b), Lambda being a hadronic scale and m_b the b quark mass, in the denominators of internal particle propagators without expansion, the resultant strong phase can accommodate the data of the B^0 -> K^-+ pi^+- direct CP asymmetry. Our study reconciles the opposite conclusions on the real or complex penguin annihilation amplitude drawn in the soft-collinear effective theory and in the perturbative QCD approach based on k_T factorization theorem.

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arXiv2007

Next-to-leading-order corrections to exclusive processes in $k_T$ factorization

We calculate next-to-leading-order (NLO) corrections to exclusive processes in $k_T$ factorization theorem, taking $πγ^*\toγ$ as an example. Partons off-shell by $k_T^2$ are considered in both the quark diagrams from full QCD and the effective diagrams for the pion wave function. The gauge dependences in the above two sets of diagrams cancel, when deriving the $k_T$-dependent hard kernel as their difference. The gauge invariance of the hard kernel is then proven to all orders by induction. The light-cone singularities in the $k_T$-dependent pion wave function are regularized by rotating the Wilson lines away from the light cone. This regularization introduces a factorization-scheme dependence into the hard kernel, which can be minimized in the standard way. Both the large double logarithms $\ln^2k_T$ and $\ln^2 x$, $x$ being a parton momentum fraction, arise from the loop correction to the virtual photon vertex, the former being absorbed into the pion wave function and organized by the $k_T$ resummation, and the latter absorbed into a jet function and organized by the threshold resummation. The NLO corrections are found to be only few-percent for $πγ^*\toγ$, if setting the factorization scale to the momentum transfer from the virtual photon.

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arXiv2007

Factorization Approaches to B Meson Decays

We compare the theoretical frameworks and the phenomenological applications of the factorization approaches to exclusive $B$ meson decays, which include QCD-improved factorization, perturbative QCD, and soft-collinear effective theory. Recent progress on two-body nonleptonic $B$ meson decays made in these approaches are reviewed.

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arXiv2007

Fourth Generation CP Violation Effect on B -> K pi, phi K and rho K in NLO PQCD

We study the effect from a sequential fourth generation quark on penguin-dominated two-body nonleptonic B meson decays in the next-to-leading order perturbative QCD formalism. With an enhancement of the color-suppressed tree amplitude and possibility of a new CP phase in the electroweak penguin, we can account better for A_{CP}(B^0 -> K^+ pi^-)-A_{CP}(B^+ -> K^+ pi^0). Taking |V_{t's}V_{t'b}| \sim 0.02 with phase just below 90^\circ, which are consistent with the b -> s l^+ l^- rate and the B_s mixing parameter Δm_{B_s}, we find a downward shift in the mixing-induced CP asymmetries of B^0 -> K_S pi^0 and phi K_S. The predicted behavior for B^0 -> rho^0 K_S is opposite.

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arXiv2007

Penguin pollution in the B^0 -> J/psi K_S decay

We present the most complete analysis of the penguin correction to the extraction of the standard-model parameter sin(2ϕ_1) from the B^0 -> J/psi K_S decay up to leading power in 1/m_b and to next-to-leading order in α_s, ϕ_1 being the weak phase, m_b the b quark mass, and α_s the strong coupling constant. The deviation ΔS_{J/psi K_S} of the mixing-induced CP asymmetry from sin(2ϕ_1) and the direct CP asymmetry A_{J/psi K_S} are both found to be of O(10^{-3}) in a formalism that combines the QCD-improved factorization and perturbative QCD approaches. The above results, different from those of O(10^{-4}) and of O(10^{-2}) obtained in the previous calculations, provide an important standard-model reference for verifying new physics from the B^0 -> J/psi K_S data.

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arXiv2007

Gluonic contribution to $B\to η^{(\prime)}$ form factors

We calculate the flavor-singlet contribution to the $B\toη^{(\prime)}$ transition form factors from the gluonic content of the $η^{(\prime)}$ meson in the large-recoil region using the perturbative QCD approach. The formulation for the $η$-$η'$ mixing in the quark-flavor and singlet-octet schemes is compared, and employed to determine the chiral enhancement scales associated with the two-parton twist-3 $η^{(\prime)}$ meson distribution amplitudes. It is found that the gluonic contribution is negligible in the $B\toη$ form factors, and reaches few percents in the $B\toη'$ ones. Its impact on the accommodation of the measured $B\toη^{(\prime)} K$ branching ratios in the perturbative QCD and QCD-improved factorization approaches is elaborated.

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arXiv2006

Penguin-dominated B -> PV decays in NLO perturbative QCD

We study the penguin-dominated B -> PV decays, with P (V) representing a pseudo-scalar (vector) meson, in the next-to-leading-order (NLO) perturbative QCD (PQCD) formalism, concentrating on the B -> K phi, pi K^*, rho K, and omega K modes. It is found that the NLO corrections dramatically enhance the B -> rho K, omega K branching ratios, which were estimated to be small under the naive factorization assumption. The patterns of the direct CP asymmetries A_{CP}(B^0 -> rho^\mp K^\pm) \approx A_{CP}(B^\pm -> rho^0 K^\pm) and |A_{CP}(B^0 -> pi^\mp K^{*\pm})| > |A_{CP}(B^\pm -> pi^0 K^{*\pm})| are predicted, differing from |A_{CP}(B^0 -> pi^\mp K^\pm)| >> |A_{CP}(B^\pm -> pi^0 K^\pm)|. The above patterns, if confirmed by data, will support the source of strong phases from the scalar penguin annihilation in PQCD. The results for the mixing-induced CP asymmetries S_f are consistent with those obtained in the literature, except that our S_{rho^0 K_S} is as low as 0.5.

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arXiv2006

Puzzles in $B$ physics

I discuss some puzzles observed in exclusive $B$ meson decays, concentrating on the large difference between the direct CP asymmetries in the $B^0\to π^\mp K^\pm$ and $B^\pm\to π^0 K^\pm$ modes, the large $B^0\toπ^0π^0$ branching ratio, and the large deviation of the mixing-induced CP asymmetries in the $b\to sq\bar q$ penguins from those in the $b\to c\bar c s$ trees.

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arXiv2006

Implication of the B -> rho rho data on the B -> pi pi puzzle

We point out that the B -> rho rho data have seriously constrained the possibility of resolving the B -> pi pi puzzle from the large observed B^0 -> pi^0 pi^0 branching ratio in the available theoretical approaches. The next-to-leading-order (NLO) contributions from the vertex corrections, the quark loops, and the magnetic penguin evaluated in the perturbative QCD (PQCD) approach have saturated the experimental upper bound of the B^0 -> rho^0 rho^0 branching ratio, and do not help. The NLO PQCD predictions for the B^0 -> rho^\mp rho^\pm and B^\pm -> rho^\pm rho^0 branching ratios are consistent with the data. The inclusion of the NLO jet function from the soft-collinear effective theory into the QCD-improved factorization approach, though enhancing the B^0 -> pi^0 pi^0 branching ratio sufficiently, overshoots the bound of the B^0 -> rho^0 rho^0 branching ratio, and deteriorates the predictions for the B^\pm -> pi^0 K^\pm and B^0 -> pi^\mp K^\pm direct CP asymmetries.

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arXiv2005

Resolution to the B -> pi K puzzle

We calculate the important next-to-leading-order contributions to the B -> pi K, pi pi decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD approach. It is found that the latter two reduce the leading-order penguin amplitudes by about 10%, and modify only the B -> pi K branching ratios. The main effect of the vertex corrections is to increase the small color-suppressed tree amplitude by a factor of 3, which then resolves the large difference between the direct CP asymmetries of the B^0 -> pi^\mp K^\pm and B^\pm -> pi^0 K^\pm modes. The puzzle from the large B^0 -> pi^0 pi^0 branching ratio still remains.

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arXiv2005

Resolution to the $B\toϕK^*$ polarization puzzle

We resolve the $B\toϕK^{*}$ polarization puzzle by postulating a smaller $B\to K^*$ form factor $A_0\approx 0.3$ and by adding penguin annihilation and nonfactorizable contributions from the perturbative QCD approach. If this explanation is valid, the penguin-dominated modes governed by the $B\to K^*$ form factors, such as $B^+\to K^{*+} K^{*0}$ and $B^0\to K^{*0} {\bar K}^{*0}$, should exhibit similar polarization fractions. Our resolution is compared with others in the literature, and experimental discrimination is proposed.

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arXiv2005

Polarizations in B -> VV decays

We demonstrate that the polarization fractions of most tree-dominated $B\to VV$ decays can be simply understood by means of kinematics in the heavy-quark or large-energy limit. For example, the longitudinal polarization fractions $R_L$ of the $B^0\to (D_s^{*+}, D^{*+}, ρ^+)D^{*-}$ and $B^+\to (D_s^{*+}, D^{*+}, ρ^+)ρ^0$ modes increase as the masses of the mesons $D_s^{*+}, D^{*+}, ρ^+$ emitted from the weak vertex decrease. The subleading finite-mass or finite-energy corrections modify these simple estimates only slightly. Our predictions for the $B\to D_{(s)}^* D^*$ polarization fractions derived in the perturbative QCD framework, especially $R_L\sim 1$ for $B^0\to {\bar D}^{*0} D^{*0}$ governed by nonfactorizable $W$-exchange amplitudes, can be confronted with future data. For penguin-dominated modes, such as $B\toρ(ω) K^*$, the polarization fractions can be understood by the annihilation effect from the $(S-P)(S+P)$ operators, plus the interference with a small tree amplitude. At last, we comment on the various mechanism proposed in the literature to explain the abnormal $B\to ϕK^*$ polarization data, none of which are satisfactory.

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arXiv2005

Weak phases from the $B\to ππ$, $Kπ$ decays

Recent data of two-body nonleptonic $B$ meson decays allow a topological-amplitude analysis up to the $O(λ^2)$ accuracy, where $λ$ denotes the Wolfenstein parameter. We find a solution from the $B\toππ$ data and a solution from the $B\to Kπ$ data, which satisfy the approximate SU(3) flavor symmetry. These solutions indicate that the color-suppressed tree amplitude is large, all other amplitudes can be understood within the standard model, and the weak phases $ϕ_2\approx 90^o$ and $ϕ_3\approx 60^o$ are consistent with the global unitarity triangle fit.

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arXiv2004

$B$ meson wave function in $k_T$ factorization

We study the asymptotic behavior of the $B$ meson wave function in the framework of $k_T$ factorization theorem. We first construct a definition of the $k_T$-dependent $B$ meson wave function, which is free of light-cone divergences. Next-to-leading-order corrections are then calculated based on this definition. The treatment of different types of logarithms in the above corrections, including the Sudakov logarithms, and those depending on a renormalization scale and on an infrared regulator, is summarized. The criticism raised in the literature on our resummation formalism and Sudakov effect is responded. We show that the $B$ meson wave function remains normalizable after taking into account renormalization-group evolution effects, contrary to the observation derived in the collinear factorization theorem.

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arXiv2004

$k_T$ factorization of exclusive $B$ meson decays

I review recent progress on exclusive $B$ meson decays made in the perturbative QCD approach, concentrating on the evolution of the $B$ meson wave function in $k_T$ factorization, radiative decays, polarizations in $VV$ modes, and new physics effect in $B\to ϕK_S$.

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arXiv2004

Vector-pseudoscalar two-meson distribution amplitudes in three-body $B$ meson decays

We study three-body nonleptonic decays $B\to VVP$ by introducing two-meson distribution amplitudes for the vector-pseudoscalar pair, such that the analysis is simplified into the one for two-body decays. The twist-2 and twist-3 $ϕK$ two-meson distribution amplitudes, associated with longitudinally and transversely polarized $ϕ$ mesons, are constrained by the experimental data of the $τ\toϕKν$ and $B\toϕKγ$ branching ratios. We then predict the $B\toϕKγ$ and $B\toϕϕK$ decay spectra in the $ϕK$ invariant mass. Since the resonant contribution in the $ϕK$ channel is negligible, the above decay spectra provide a clean test for the application of two-meson distribution amplitudes to three-body $B$ meson decays.

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arXiv2004

Transition to perturbative QCD in two-photon collisions

We propose that the different angular distributions in two-photon collisions observed at low and high center-of-mass energies $W_{γγ}$ indicate the transition from nonperturbative to perturbative QCD. We calculate the differential cross sections of $γγ\toππ$, $KK$ in the angle $θ$ of one of the final-state mesons using QCD sum rules and the perturbative QCD approach based on $k_T$ factorization theorem. Our predictions from sum rules (perturbative QCD) decrease (increase) with $|\cosθ|$, consistent with the Belle data of $γγ\to K^+K^-$ for $W_{γγ}\approx 1.5$-1.7 (2.2-2.4) GeV.

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