arXiv subjects

Run-Hui Li

Publications and source records attributed to Run-Hui Li.

35 records · Page 2Linked to original sources

arXiv2017

Nonleptonic charmless decays of $B_c\to TP, TV$ in the perturbative QCD approach

Two-body charmless hadronic $B_c$ decays involving a light $1^3\!P_2$-tensor($T$) meson are investigated for the first time within the framework of perturbative QCD(pQCD) at leading order, in which the other meson is the lightest pseudoscalar($P$) or vector($V$) state. The concerned processes can only occur through the pure weak annihilation topology in the standard model. We predict the CP-averaged branching ratios and polarization fractions of those considered decays in Cabibbo-Kobayashi-Maskawa(CKM) favored and suppressed modes. Phenomenologically, several modes$-$such as the $B_c \to K_2^*(1430) K$ and the CKM-favored $B_c \to TV-$have large decay rates of $10^{-6}$, which are expected to be detected at Large Hadron Collider experiments in the near future. Moreover, all of the $B_c \to TV$ modes are governed by the longitudinal amplitudes in the pQCD calculations and the corresponding fractions vary around $78\%$-$98\%$. A confirmation of these results could prove the reliability of the pQCD approach used here and further shed some light on the annihilation decay mechanism.

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arXiv2017

Doubly-Heavy Baryon Weak Decays: $Ξ_{bc}^{0}\to pK^{-}$ and $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$

Doubly-heavy baryons, with two heavy and one light quarks, are expected to exist in QCD and their masses have been predicted in the quark model. However their existence is not well established so far in experiment. In this work, we explore the possibility of searching for $Ξ_{bc}$ and $Ξ_{cc}^{+}$ in the $W$-exchange processes, $Ξ_{bc}^{0}\to pK^{-}$ and $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$. On the basis of perturbative calculations, we estimate the branching ratio of the first decay as ${\cal BR}(Ξ_{bc}^0\to p^+ K^-)\approx3.21\times {\cal R}^2_f \times {\cal R}_τ\times 10^{-7}$, where ${\cal R}_f$ (${\cal R}_τ$) are the ratios of the decay constants (lifetimes) of $Ξ_{bc}^{0}$ and $Λ_b^{0}$. The branching ratio of $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$ is related to that of $Λ_c^+\to Δ^{++} K^-$, and thereby a conjectured topology analysis leads to the range for the branching ratio as: ${\cal BR}(Ξ_{cc}^+\to Σ_{c}^{++}(2520) K^-)\in \left[0.36\%,1.80\%\right]$. The decay $Ξ_{cc}^+\to Σ_{c}^{++}(2520) K^-$ would be reconstructed in the $ Λ_{c}^{+}K^{-}π^{+}$ final state which is easy to access even at a hadron collider. Based on the two facts that abundant heavy quarks can be produced at a hadron collider like LHC, and the branching ratios of $Ξ_{bc}^{0}\to pK^{-}$ and $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$ are sizable, we urge our experimental colleagues to perform a search at LHCb. This will presumably lead to the discovery of the $Ξ_{bc}$ and $Ξ_{cc}^{+}$ , and precision measurements of the branching ratios in the future are helpful to investigate their decay mechanism.

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arXiv2013

$B\to DK^*_{0,2}$ Decays: PQCD analysis to determine CP violation phase angle $γ$

$B^\pm \to (D^0, \bar D^0, D_{CP})K^{*\pm}_{0,2}$ decays are helpful in determining the CP violation angle $γ$, and we analyze these decay processes within the perturbative QCD approach based on $k_T$ factorization. We found that the branching ratio of $B^-\to D^0 K^{*-}_0$ can reach the order of $10^{-4}$, due to the enhancement of nonfactorizable contributions in color-suppressed $D^0$-emission, while the branching ratio of $B^-\to \bar D^0 K^{*-}_0$ is of the order $10^{-5}$. The ratio of decay amplitudes is about 3 times larger than the one in the channel $B^\pm\to D K^\pm$. Large branching ratios provide a good opportunity to observe $ B^\pm \to D K^{*\pm}_2$ on the ongoing and forthcoming experimental facilities and consequently these channels may be of valuable avail in reducing the errors in the CP violation phase angle $γ$. We also explore the possible time-dependent CP asymmetries of $B_s$ decay into a scalar meson to determine the phase angle $γ$.

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arXiv2011

Rare B decays and Tevatron top-pair asymmetry

The recent Tevatron result on the top quark forward-backward asymmetry, which deviates from its standard model prediction by 3.4$σ$, has prompted many authors to build new models to account for this anomaly. Among the various proposals, we find that those mechanisms which produce $t\bar t$ via $t$- or $u$-channel can have a strong correlation to the rare B decays. We demonstrate this link by studying a model with a new charged gauge boson, $W'$. In terms of the current measurements on $B\to πK$ decays, we conclude that the branching ratio for $B^-\to π^- \bar K^0$ is affected most by the new effects. Furthermore, using the world average branching ratio for the exclusive B decays at $2σ$ level, we discuss the allowed values for the new parameters. Finally, we point out that the influence of the new physics effects on the direct CP asymmetry in B decays is insignificant.

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arXiv2011

Study of $\bar B^0 \to D^0 μ^+μ^-$ Decay in Perturbative QCD Approach

Within the perturbative QCD approach and ignoring the contributions of long distance and subleading penguin loops, we investigate $\bar B^0 \to D^0 μ^+μ^-$ decay in the large recoiling kinematic region in the Standard Model. At the tree level, $\bar B^0$ decays to $D^0$ by exchanging a $W$ boson accompanied by a virtual photon emission from the valence quarks of $\bar B^0$ and $D^0$ meson, then the virtual photon decays to the lepton pair. Numerically, we find that the branching ratio decreases rapidly as the $q^2$ increases, and the branching ratio of $ \bar B^0\to D^0μ^+μ^-$ is $(9.7_{-3.2}^{+4.2})\times 10^{-6}$ in the region $q^2 \in [1,5] \mathrm{GeV}^2$. The order of the branching ratio shows a possibility to study this interesting channel in the current $B$ factories and the Large Hadron Collider. The precise experimental data will help us to test the factorization approach and the QCD theory, in general.

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arXiv2011

Study of $B\to K^{(*)} \ell^+\ell^-$ Decays in the Family Non-universal $Z'$ Models

In a combined investigation of the $B\to K^{(*)}\ell^+\ell^-$ decays, constraints on the related couplings in family non-universal $Z^{\prime}$ models are derived. We find that within the allowed parameter space, the recently observed forward-backward asymmetry in the $B\to K^*\ell^+\ell^-$ decay can be explained, by flipping the signs of the Wilson coefficients $C_9^{\rm eff}$ and $C_{10}$. With the obtained constraints, we also calculate the branching ratio of the $B_s\toμ^+μ^-$ decay. The upper bound of our prediction is near the upper bound given by CDF Collaboration recently.

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arXiv2011

Branching ratios, forward-backward asymmetries and angular distributions of $B\to K_2^*l^+l^-$ in the standard model and new physics scenarios

We analyze the $B\to K_2^*(\to Kπ)l^+l^-$ (with $l=e,μ,τ$) decay in the standard model and two new physics scenarios: vector-like quark model and family non-universal $Z'$ model. We derive its differential angular distributions, using the recently calculated form factors in the perturbative QCD approach. Branching ratios, polarizations, forward-backward asymmetries and transversity amplitudes are predicted, from which we find a promising prospective to observe this channel on the future experiment. We also update the constraints on effective Wilson coefficients and/or free parameters in these two new physics scenarios by making use of the experimental data of $B\to K^*l^+l^-$ and $b\to sl^+l^-$. Their impact on $B\to K_2^*l^+l^-$ is subsequently explored and in particular the zero-crossing point for the forward-backward asymmetry in these new physics scenarios can sizably deviate from the SM scenario. In addition we also generalize the analysis to a similar mode $B_s\to f_2'(1525)(\to K^+K^-) l^+l^-$.

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arXiv2010

Charge and CP asymmetries of $B_q$ meson in unparticle physics

Recently the DØ Collaboration reported an observation of like-sign charge asymmetry (CA), which is about $3.2 σ$ deviation from the standard model (SM) prediction. Inspired by the observation we investigate the scalar unparticle effects, under the color charge of $SU(3)_c$ symmetry, in the CP violation in neutral B meson oscillations as well as the dispersive and absorptive parts of $\bar B_q\leftrightarrow B_q$ transition, which can be related to the CA directly. In order to illustrate the peculiar properties of unparticle, our analysis is carried out in two scenarios for the right-handed section: (I) $λ_R=λ_L$ and $U_D^R=U_D^L$, where $λ_{L,R}$ and $U_D^{L,R}$ are the couplings and flavor mixing matrix of left- and right-handed section, respectively; (II) $λ_R >> λ_L$ and $U_D^R$ is completely a free parameter. In scenario I we found that the wrong- and like-sign CA cannot be changed significantly for a SM-like CP violating source because of the strong constraint of $Δm_{B_d}$. Contrarily, in scenario II we can figure out the parameter space in which the CA can be enhanced to the value observed by DØ with the constraint of $Δm_{B_s}$ due to the enhancement of $Γ^s_{12}$. In the parameter space we obtained, the correlation between $ΔΓ^s$ and $ϕ_s$ is consistent with the current CDF and DØ results.

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arXiv2010

Decays of $B$ meson to two charmed mesons

The factorization theorem in Decays of $B_{(s)}$ mesons to two charmed mesons (both pseudoscalar and vector) can still be proved in the leading order in $m_D/m_B$ and $Λ_{\rm{QCD}}/m_D$ expansion. Working in the perturbative QCD approach, we find that the factorizable emission diagrams are dominant. Most of branching ratios we compute agree with the experimental data well, which means that the factorization theorem seems to be reliable in predicting branching ratios for these decays. In the decays of a $B$ meson to two vector charmed mesons, the transverse polarization states contribute $40%-50%$ both in the processes with an external W emission and in the pure annihilation decays. This is in agreement with the present experimental data. We also calculate the CP asymmetry parameters. The results show that the direct CP asymmetries are very small. Thus observation of any large direct CP asymmetry will be a signal for new physics. The mixing induced CP asymmetry in the neutral modes is large. This is also in agreement with the current experimental measurements. They can give a cross check of the $\sin 2β$ measurement from other channels.

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arXiv2009

The CKM suppressed $B(B_s) \to \bar D_{(s)}P,\bar D_{(s)}V,\bar D_{(s)}^P, \bar D_{(s)}^V$ decays in perturbative QCD approach

Although the two-body charmed decays $B_{(s)} \to \bar D_{(s)}^{(*)}P$ and $\bar D_{(s)}^{(*)}V$, where $P$($V$) denotes a light pseudoscalar(vector) meson, are CKM suppressed comparing with the $B_{(s)} \to D_{(s)}^{(*)}P$ and $ D_{(s)}^{(*)}V$ decays, they are important in the CKM angle $γ=ϕ_3$ extraction method. We investigated these decays in the perturbative QCD approach to the leading order of $m_D/m_B$ and $Λ_{\rm{QCD}}/m_D$ expansion. We find that the nonfactorizable emission diagrams and the annihilation diagrams are not negligible in many of these channels. The numerical results show that most channels have branching ratios with an order of $10^{-6}$ or $10^{-7}$. The ratio needed for the CKM angle $γ$ extraction is estimated as $r = \frac{|A(B^- \to \bar{D}^0 K^-)|}{|A(B^- \to D^0 K^-)|} = 0.092_{-0.003-0.003}^{+0.012+0.003},$ which is too small for the experiments. Some of the $ B_{(s)}\to \bar D_{(s)}^*V$ decays have a very large transversely polarized contribution that can reach 80%.

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arXiv2009

Branching Ratios, Forward-backward Asymmetry and Angular Distributions of $B\to K_1l^+l^-$ Decays

Using the $B\to K_1$ form factors evaluated in the perturbative QCD approach, we study semileptonic $B\to K_1(1270)l^+l^-$ and $B\to K_1(1400)l^+l^-$ decays, where $K_1(1270)$ and $K_1(1400)$ are mixtures of $K_{1A}$ and $K_{1B}$ which are $^3P_1$ and $^1P_1$ states, respectively. Using the technique of helicity amplitudes, we express the decay amplitudes in terms of several independent and Lorentz invariant pieces. We study the dilepton invariant mass distributions, branching ratios, polarizations and forward-backward asymmetries of $ B\to K_1l^+l^-$ decays. The ambiguity in the sign of the mixing angle will induce much large differences to branching ratios of semileptonic B decays: branching ratios without resonant contributions either have the order of $10^{-6}$ or $10^{-8}$. But the polarizations and the forward-backward asymmetries are not sensitive to the mixing angles. We find that the resonant contributions will dramatically change the dilepton invariant mass distributions in the resonant region. We also provide the angular distributions of $ B\to K_1l^+l^-\to (Kππ)l^+l^-$ decays.

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arXiv2009

Exclusive $B_s$ decays to the charmed mesons $D_s^+(1968,2317)$ in the standard model

The transition form factors of $\bar B_s^0\to D_{s}^+(2317)$ and $\bar B_s^0\to D_s^+(1968)$ at large recoil region are investigated in the light cone sum rules approach, where the heavy quark effective theory is adopted to describe the form factors at small recoil region. With the form factors obtained, we carry out a detailed analysis on both the semileptonic decays $\bar B_s^0\to D_s^+(1968,2317) l \barν_l$ and nonleptonic decays $B_s \to D_s^+(1968,2317) M$ with $M$ being a light meson or a charmed meson under the factorization approach. Our results show that the branching fraction of $\bar B_s^0\to D_s^+(2317) μ\barν_μ$ is around $2.3 \times 10^{-3}$, which should be detectable with ease at the Tevatron and LHC. It is also found that the branching fractions of $\bar B_s^0\to D_s^+(1968) l \barν_l$ are almost one order larger than those of the corresponding $B_s^0\to D_s^+(2317) l \barν_l$ decays. The consistency of predictions for $B_s \to D_s^+(1968,2317) L$ ($L$ denotes a light meson) in the factorization assumption and $k_T$ factorization also supports the success of color transparency mechanism in the color allowed decay modes. Most two-charmed meson decays of $B_s$ meson possess quite large branching ratios that are accessible in the experiments. These channels are of great importance to explore the hadronic structure of charmed mesons as well as the nonperturbative dynamics of QCD.

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arXiv2009

Transition form factors of B decays into p-wave axial-vector mesons in the perturbative QCD approach

The $B_{u,d,s}\to V,A$ form factors are studied in perturbative QCD approach ($V,A$ denote a vector meson and two kinds of p-wave axial-vector mesons: $^3P_1$ and $^1P_1$ states, respectively.). The form factors are directly studied in the large recoiling region and extrapolated to the whole kinematic region within the dipole parametrization. Adopting decay constants with different signs for the two kinds of axial-vectors, we find that the two kinds of $B\to A$ form factors have the same sign. The two strange mesons $K_{1A}$ and $K_{1B}$ mix with each other via the SU(3) symmetry breaking effect. In order to reduce the ambiguities in the mixing angle between $K_{1A}$ and $K_{1B}$, we propose a model-independent way that utilizes the B decay data. Most of the branching fractions of the semilteptonic $B\to Al\bar ν_l$ decays are of the order $10^{-4}$, which still need experimental tests in the on-going and forthcoming experiments.

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arXiv2008

$B\to S$ Transition Form Factors in the PQCD approach

Under two different scenarios for the light scalar mesons, we investigate the transition form factors of $B(B_s)$ mesons decay into a scalar meson in the perturbative QCD approach. In the large recoiling region, the form factors are dominated by the short-distance dynamics and can be calculated using perturbation theory. We adopt the dipole parametrization to recast the $q^2$ dependence of the form factors. Since the decay constants defined by the scalar current are large, our predictions on the $B\to S$ form factors are much larger than the $B\to P$ transitions, especially in the second scenario. Contributions from various light-cone distribution amplitudes (LCDAs) are elaborated and we find that the twist-3 LCDAs provide more than a half contributions to the form factors. The two terms of the twist-2 LCDAs give destructive contributions in the first scenario while they give constructive contributions in the second scenario. With the form factors, we also predict the decay width and branching ratios of the semileptonic $B\to Sl\barν$ and $B\to Sl^+l^-$ decays. The branching ratios of $B\to Sl\barν$ channels are found to have the order of $10^{-4}$ while those of $B\to Sl^+l^-$ have the order of $10^{-7}$. These predictions can be tested by the future experiments.

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arXiv2008

What can we learn from $B\to a_1(1260)(b_1(1235))π(K)$ decays?

We investigate the $B\to a_1(1260)(b_1(1235))π(K)$ decays under the factorization scheme and find many discrepancies between theoretical predictions and the experimental data. In the tree dominated processes, large contributions from color-suppressed tree diagrams are required in order to accommodate with the large decay rates of $B^-\to a_1^0π^-$ and $B^-\to a_1^-π^0$. For $\bar B^0\to (a_1^+, b_1^+)K^-$ decays which are both induced by $b\to s$ transition, theoretical predictions on their decay rates are larger than the data by a factor of 2.8 and 5.5, respectively. Large electro-weak penguins or some new mechanism are expected to explain the branching ratios of $B^-\to b_1^0K^-$ and $B^-\to a_1^-\bar K^0$. The soft-collinear-effective-theory has the potential to explain large decay rates of $B^-\to a_1^0π^-$ and $B^-\to a_1^-π^0$ via a large hard-scattering form factor $ζ_J^{B\to a_1}$. We will also show that, with proper charming penguins, predictions on the branching ratios of $\bar B^0\to (a_1^+, b_1^+)K^-$ can also be consistent with the data.

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arXiv2008

The $B(B_s)\to D_{(s)} P$, $D_{(s)} V$, $D_{(s)}^{}P$ and $D_{(s)}^{}V$ decays in the perturbative QCD approach

Two-body non-leptonic charmed decays $B_{(s)} \to D_{(s)}P$, $D_{(s)}^*P$, $D_{(s)}V$ and $D_{(s)}^*V$ are analyzed in perturbative QCD approach, where $P$ and $V$ denote the light pseudoscalar meson and vector meson, respectively. We test the $D$ meson wave function by a $χ^2$ fit with experimental data of six $B\to DP$ channels. We give the branching ratios of all the charmed B decay channels, most of which agree with experiments amazingly well. The predicted $B_s$ decays can be confronted with the future experimental data. By straightforward calculations, our pQCD approach gives the right relative strong phase of $a_2/a_1$ with experiments. We also predict the percentage of transverse polarizations in $B_{(s)} \to D^* V$ decay channels.

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arXiv2007

Radiative charmless B_{(s)}\to V γand B_{(s)}\to A γdecays in pQCD approach

We study the radiative charmless $B_{(s)}\to V(A)γ$ decays in perturbative QCD (pQCD) approach to the leading order in $α_s$ (here $V$ and $A$ denotes vector mesons and two kinds of axial-vector mesons: $^3P_1$ and $^1P_1$ states, respectively.). Our predictions of branching ratios are consistent with the current available experimental data. We update all $B_{(s)}\to V$ form factors and give the predictions for $B\to A$ form factors using the recent hadronic inputs. In addition to the dominant factorizable spectator diagrams, which is form factor like, we also calculate the so-called ``power suppressed'' annihilation type diagrams, the gluonic penguin, charming penguin, and two photon diagrams. These diagrams give the main contributions to direct CP asymmetries, mixing-induced CP asymmetry variables, the isospin asymmetry and U-spin asymmetry variables. Unlike the branching ratios, these ratios or observables possess higher theoretical precision in our pQCD calculation, since they do not depend on the input hadronic parameters too much. Most of the results still need experimental tests in the on-going and forthcoming experiments.

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