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Hai-Yang Cheng

Publications and source records attributed to Hai-Yang Cheng.

At least 127 records · Page 7Linked to original sources
arXiv2005

Penguin-induced Radiative Baryonic B Decays Revisited

Weak radiative baryonic B decays $\bar B\to B_1\bar B_2γ$ mediated by the electromagnetic penguin process $b\to sγ$ 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 $Σ\bar pγ$ mode and is comparable to the baryon pole effect in $Λ\bar pγ$ and $Ξ\barΛγ$ modes. The branching ratios for $B^-\toΛ\bar pγ$ and $B^-\toΞ^0\barΣ^-γ$ 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 $B^-\toΛ\bar pγ$. 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 $B\toΞ\barΣγ$, a large correlation of the photon to the $\barΣ$ and a broad bump in the dibaryon mass spectrum are predicted.

hep-ph↗
arXiv2005

CP-violating asymmetries in B^0 decays to K^+K^-K_{S(L)}^0 and K_S^0K_S^0K_{S(L)}^0

Decay rates and time-dependent and direct CP asymmetries in the decays $B^0\to K^+K^-K_{S(L)}$ and $K_S K_S K_{S(L)}$ are studied. Resonant and nonresonant contributions to the three-body decays are carefully investigated. Nonresonant effects on 2-body and 3-body matrix elements are constrained by QCD counting rules. The predicted branching ratios are consistent with the data within the theoretical and experimental errors, though the theoretical central values are somewhat smaller than the experimental ones. Owing to the presence of color-allowed tree amplitudes in $B^0\to K^+K^-K_{S(L)}$, this penguin-dominated mode is subject to a significant tree pollution and the deviation of the mixing-induced \CP asymmetry from that measured in $B\to J/ψK_S$, namely, $Δ\sin 2β_{K^+K^-K_{S(L)}}\equiv \sin 2β_{K^+K^-K_{S(L)}}-\sin 2 β_{J/ψK_S}$, can be as large as O(0.10). In contrast, the $K_SK_SK_{S(L)}$ modes appear theoretically very clean in our picture with negligible $Δ\sin 2β_{K_SK_SK_{S(L)}}$. Direct CP asymmetries in $K^+K^-K_{S(L)}$ and $K_S K_S K_{S(L)}$ modes are found to be very small.

hep-ph↗
arXiv2005

Effects of Final-state Interactions on Mixing-induced CP Violation in Penguin-dominated B Decays

Motivated by the recent indications of the possibility of sizable deviations of the mixing-induced CP violation parameter, $S_f$, in the penguin-dominated $b\to sq\bar q$ transition decays such as $B^0\to (ϕ,ω,ρ^0,η',η,π^0,f_0)K_S$ from $\sin 2β$ determined from $B\to J/ψK_S$, we study final-state rescattering effects on their decay rates and CP violation. Recent observations of large direct CP asymmetry in modes such as $B^0\to K^+π^-,ρ^-π^+$ means that final state phases in 2-body B decays may not be small. It is therefore important to examine these long-distance effects on penguin-dominated decays. Such long-distance effects on $S_f$ are found to be generally small [i.e. ${\cal O}(1-2%)$] or negligible except for the $ωK_S$ and $ρ^0K_S$ modes where $S_f$ is lowered by around 15% for the former and increased by the same percentage for the latter. However, final-state rescattering can enhance the $ωK_S, ϕK_S, η'K_S, ρ^0K_S$ and $π^0K_S$ rates significantly and flip the signs of direct CP asymmetries of the last two modes. Direct CP asymmetries in $ωK_S$ and $ρ^0K_S$ channels are predicted to be $\A_{ωK_S}\approx -0.13$ and $\A_{ρ^0K_S}\approx 0.47$, respectively. However, direct CP asymmetry in all the other $b\to s$ penguin dominated modes that we study is found to be rather small (a few percents), rendering these modes a viable place to search for the CP-odd phases beyond the standard model.

hep-ph↗
arXiv2005

$B\to f_0(980)K$ Decays and Subleading Corrections

The decay $B\to f_0(980)K is studied within the framework of QCD factorization and the two-quark scenario for $f_0(980)$. There are two distinct penguin contributions and their interference depends on the unknown mixing angle $θ$ of strange and nonstrange quark contents of $f_0(980)$: destructive for $0<θ<π/2$ and constructive for $π/2<θ<π$. The QCD sum rule method is applied to evaluate the leading-twist light-cone distribution amplitudes and the scalar decay constant of $f_0$. We conclude that the short-distance approach is not adequate to explain the observed large rates of $f_0K^-$ and $f_0\ov K^0$. Among many possible subleading corrections, we study and estimate the contributions from the three-parton Fock states of the $f_0$ and from the intrinsic gluon inside the $B$ meson. It is found that the spectator gluon of the $B$ meson may play an eminent role for the enhancement of $f_0(980)K$. We point out that if $f_0(980)$ is a four-quark state as widely perceived, there will exist extra diagrams contributing to $B\to f_0(980)K$. However, in practice it is difficult to make quantitative predictions based on the four-quark picture for $f_0(980)$ as it involves additional nonfactorizable contributions that are difficult to estimate and the calculations of the decay constant and form factors of $f_0(980)$ are beyond the conventional quark model.

hep-ph↗
arXiv2004

Final State Interactions in Hadronic B Decays

There exist many experimental indications that final-state interactions (FSIs) may play a prominent role not only in charmful B decays but also in charmless B ones. We examine the final-state rescattering effects on the hadronic B decay rates and their impact on direct CP violation. The color-suppressed neutral modes such as $B^0\to D^0π^0,π^0π^0,ρ^0π^0,K^0π^0$ can be substantially enhanced by long-distance rescattering effects. The direct CP-violating partial rate asymmetries in charmless B decays to $ππ/πK$ and $ρπ$ are significantly affected by final-state rescattering and their signs are generally different from that predicted by the short-distance approach. For example, direct CP asymmetry in $B^0\toρ^0π^0$ is increased to around 60% due to final state rescattering effects whereas the short-distance picture gives about 1%. Evidence of direct CP violation in the decay $\bar B^0\to K^-π^+$ is now established, while the combined BaBar and Belle measurements of $\bar B^0\toρ^\pmπ^\mp$ imply a $3.6σ$ direct CP asymmetry in the $ρ^+π^-$ mode. Our predictions for CP violation agree with experiment in both magnitude and sign, whereas the QCD factorization predictions seem to have some difficulty with the data. Current data on $πK$ modes seem to violate the isospin sum rule relation, suggesting the presence of electroweak penguin contributions. We have also investigated whether a large transverse polarization in $B\to ϕK^*$ can arise from the final-state rescattering of $D^{(*)}\bar D_s^{(*)}$ into $ϕK^*$.

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arXiv2004

Light-Front Approach for Pentaquark Strong Decays

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, we study the strong decays of light and heavy parity-even pentaquark states using the light-front quark model in conjunction with the spectator approximation. The narrowness of the Theta width is ascribed to the p-wave configuration of the diquark pair. Taking the Theta width as a benchmark, we estimate the rates of the strong decays Xi_{3/2}-- to Xi- pi-, Sigma- K-, Sigma_{5c}0 to D_s- p, D_{s0}*- p and Xi_{5c}0 to D_s- Sigma+, D_{s0}^{*-} Sigma+ with Sigma_{5c} Xi_{5c} being antisextet charmed pentaquarks and D_{s0}* a scalar strange charmed meson. The ratio of Gamma(P_c to Baryon D_{s0}*)/Gamma(P_c to Baryon D_s) is very useful for verifying the parity of the antisextet charmed pentaquark P_c. It is expected to be of order unity for an even parity P_c and much less than one for an odd parity pentaquark.

hep-ph↗
arXiv2004

Light-Front Approach for Heavy Pentaquark Transitions

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.

hep-ph↗
arXiv2004

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.

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arXiv2004

Covariant Light-Front Approach for s-wave and p-wave Mesons: Its Application to Decay Constants and Form Factors

We study the decay constants and form factors of the ground-state s-wave and low-lying p-wave mesons within a covariant light-front approach. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or p-wave meson and their momentum dependence are presented in detail. In particular, form factors for heavy-to-light and B to D** transitions, where D** denotes generically a p-wave charmed meson, are compared with other model calculations. The experimental measurements of the decays B^- to D** pi^- and B to D D**_s are employed to test the decay constants of D**_s and the B to D** transition form factors. The heavy quark limit behavior of the decay constants and form factors is examined and it is found that the requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW) functions, one for s-wave to s-wave and two for s-wave to p-wave transitions, are obtained. The values of IW functions at zero recoil and their slope parameters can be used to test the Bjorken and Uraltsev sum rules.

hep-ph↗
arXiv2003

Status of Exclusive Baryonic B Decays

The status of exclusive two-body and three-body baryonic B decays is reviewed. The threshold peaking effect in baryon pair invariant mass is stressed and explained. Weak radiative baryonic B decays mediated by the electromagnetic penguin process are discussed.

hep-ph↗
arXiv2003

Hadronic B Decays Involving Even Parity Charmed Mesons

Hadronic B decays containing an parity-even charmed meson in the final state are studied. Specifically we focus on the Cabibbo-allowed decays $\bar B\to D^{**} π(ρ), D^{**}\bar D_s^{(*)}, \bar D^{**}_sD^{(*)}$ and $\bar B_s\to D_s^{**}π(ρ)$, where $D^{**}$ denotes generically a p-wave charmed meson. The $B\to D^{**}$ transition form factors are studied in the improved version of the Isgur-Scora-Grinstein-Wise quark model. We apply heavy quark effective theory and chiral symmetry to study the strong decays of p-wave charmed mesons and determine the magnitude of the $D_1^{1/2}-D_1^{3/2}$ mixing angle. Except the decay to $D_1(2427)^0π^-$ the predictions for $B^-\to D^{**0}π^-$ agree with experiment. The sign of $D_1^{1/2}-D_1^{3/2}$ mixing angle is found to be positive in order to avoid a severe suppression on the production of $D_1(2427)^0π^-$. The interference between color-allowed and color-suppressed tree amplitudes is expected to be destructive in the decay $B^-\to D_1(2427)^0π^-$. Hence, an observation of the ratio $D_1(2427)^0π^-/D_1(2427)^+π^-$ can be used to test the relative signs of various form factors as implied by heavy quark symmetry. Although the predicted $B^-\to D_1(2420)^0ρ^-$ at the level of $3\times 10^{-3}$ exceeds the present upper limit, it leads to the ratio $D_1(2420)ρ^-/D_1(2420)π^-\approx 2.6$ as expected from the factorization approach and from the ratio $f_ρ/f_π\approx 1.6$ . Therefore, it is crucial to have a measurement of this mode to test the factorization hypothesis. For $\bar B\to \bar D_s^{**}D$ decays, it is expected that $\bar D_{s0}^*D\gsim \bar D_{s1}D$ as the decay constants of the multiplet $(D_{s0}^*,D_{s1})$ become the same in the heavy quark limit.

hep-ph↗
arXiv2003

B Decays as Spectroscope for Charmed Four-quark States

The $D_s(2320)$ state recently observed by BaBar in the $D_s^+π^0$ channel may be the first of a host of $cq\bar q\bar q$ four-quark states. We give a phenomenological account of the masses and decay modes. The isosinglet $D_s(2320)$ state is the only narrow one, dominated by the observed isospin violating decay and less than $\sim$ 100 keV in width. All other states are expected to decay hadronically. Notable resonances are in doubly charged $D_s^+π^+$, $D^+K^+$, wrong pairing $D^+K^-$, and also $D_s^+K^-$, $Dη$ channels. We propose B decays as searching ground for such 4-quark states, which recoil against $\bar D^{(*)}$ meson from B decay, or $π^+$ $\bar D^{(*)}$, $\bar K$ mesons from $\bar B$ decay. Exotic $qc\bar c\bar q$ charmonia could also be produced, and may be behind the slow $J/ψ$ bump in inclusive $B\to J/ψ+X$ decay.

hep-ph↗
arXiv2003

Hadronic Charmed Meson Decays Involving Tensor Mesons

Charmed meson decays into a pseudoscalar meson P and a tensor meson T are studied. The charm to tensor meson transition form factors are evaluated in the Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the Cabibbo-allowed decay $D_s^+\to f_2(1270)π^+$ is dominated by the W-annihilation contribution and has the largest branching ratio in $D\to TP$ decays. We argue that the Cabibbo-suppressed mode $D^+\to f_2(1270)π^+$ should be suppressed by one order of magnitude relative to $D_s^+\to f_2(1270)π^+$. When the finite width effect of the tensor resonances is taken into account, the decay rate of $D\to TP$ is generally enhanced by a factor of $2\sim 3$. Except for $D_s^+\to f_2(1270)π^+$, the predicted branching ratios of $D\to TP$ decays are in general too small by one to two orders of magnitude compared to experiment. However, it is very unlikely that the $D\to T$ transition form factors can be enhanced by a factor of $3\sim 5$ within the ISGW quark model to account for the discrepancy between theory and experiment. As many of the current data are still preliminary and lack sufficient statistic significance, more accurate measurements are needed to pin down the issue.

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