arXiv subjects

Yu-Ming Wang

Publications and source records attributed to Yu-Ming Wang.

68 records · Page 4Linked to original sources

arXiv2008

Charmless Two-body $B(B_s)\to PP,VP$ decays In Soft-Collinear-Effective-Theory

We analyze the charmless two-body $B\to VP$ decays in the soft-collinear-effective-theory (SCET), where $V(P)$ denotes a light vector (pseudoscalar) meson. Using the current experimental data, we find two solutions in $χ^2$ fit for the 16 non-perturbative inputs responsible for the 87 $B\to PP$ and $B\to VP$ decay channels in SU(3) symmetry. Chirally enhanced penguins can only change several charming penguins sizably, since they share the same topology. The (S-P)(S+P) annihilation penguins in the perturbative QCD approach have the same topology with charming penguins in SCET, which play an important role in direct CP asymmetries.

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arXiv2008

Scalar mesons in weak semileptonic decays of $B_{(s)}$

The transition form factors of $B_{(s)} \to S$, with $S$ denoting a scalar meson, are investigated in the light-cone sum rules approach. The numerical values are approximately twice as large as that estimated in the light-front quark model and QCD sum rules approach. Using these form factors, we present the analysis of the decay rates for $B \to a_0(1450) l \barν_l $, $B \to K^{\ast}_0(1430) l \bar{l}$, $B_s \to K^{\ast}_0(1430) l \barν_l$ and $B_s \to f_0(1500) l \bar{l}$ with $l=e, μ, τ$. The results indicate that magnitudes of $BR(\bar{B}_0 \to a_0(1450) l \barν_l)$ and $BR(B_s \to K^{\ast}_0(1430) l \barν_l)$ can arrive at the order of $10^{-4}$, which can be measured in the future experiments to clarify the inner structure of scalar mesons. It is also observed that $BR(B \to K^{\ast}_0(1430) τ^+ τ^-)$ and $BR(B_s \to f_0(1500) τ^+ τ^-)$ are an order of magnitude smaller than the corresponding channels of $e^+ e^-$ and $μ^+ μ^-$ final states due to the heavily suppressed phase space . Moreover, the longitudinal lepton polarization asymmetry for $B \to K^{\ast}_0(1430) l \bar{l}$ and $B_s \to f_0(1500) l \bar{l}$ are also investigated, whose values are close to -1 for the $e^+ e^-$ and $μ^+ μ^-$ pair except the region close to the end points.

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arXiv2008

Weak productions of new charmonium in semi-leptonic decays of B_c

We study the weak productions of novel heavy mesons, such as $η_c^{\prime}$, $h_c$, $h_c^{\prime}$, $χ_{c0}^{\prime}$, X(3940), Y(3940), X(3872), and Y(4260), in the semi-leptonic $B_c$ decays. Since there is still no definite answer for the components of X(3940), Y(3940), X(3872), Y(4260) so far, we will assign them as excited charmonium states with the possible quantum numbers constrained by the current experiments. As for the weak transition form factors, we calculate them in the framework of light-cone QCD sum rules approach, which is proved to be a powerful tool to deal with the non-perturbative hadronic matrix element. Our results indicate that different interpretations of X(3940) can result in remarkable discrepancy of the production rate in the $B_c$ decays, which would help to clarify the inner structure of the X(3940) with the forthcoming LHC-b experiments. Besides, the predicted large weak production rates of X(3872) and Y(3940) in $B_c$ decays and the small semi-leptonic decay rate for $B_c \to Y(4260)$ all depend on their quantum number $J^{PC}$ assignments. Moreover, the $S-D$ mixing of various vector charmonium states in the weak decay of $B_c$ is also discussed in this work. The future experimental measurements of these decays will test the inner structures of these particles, according to our predictions here.

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arXiv2008

Weak decays of $J/ψ$: the non-leptonic case

In our previous study, we calculated the transition from factors of $J/ψ\to D^{(*)}_{(s)}$ using the QCD sum rules. Based on the factorization approximation, the obtained form factors can be applied to evaluate the weak non-leptonic decay rates of $J/ψ\to D^{(*)}_{(s)}+M$, where $M$ stands for a light pseudoscalar or vector meson. We predict that the branching ratio for inclusive non-leptonic two-body weak decays of $J/ψ$ which are realized via the spectator mechanism, can be as large as $1.3 \times 10^{-8}$, in particular, the branching ratio of $J/ψ\to D^{*\pm}_s+ρ^\mp$ can reach $5.3 \times 10^{-9}$. Such values will be marginally accessed by the ability of BESIII which will begin running very soon.

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arXiv2007

The transition form factors for semi-leptonic weak decays of $J/ψ$ in QCD sum rules

Within the Standard Model, we investigate the semi-leptonic weak decays of $J/ψ$. The various form factors of $J/ψ$ transiting to a single charmed meson ($D^{(*)}_{(d,s)}$) are studied in the framework of the QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of $J/ψ$ and provide valuable information about the non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode $J/ψ\to D^{(*)-}_{s}+e^{+}+ν_{e}$ is at order of $10^{-10}$.

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arXiv2007

Lepton flavor violating processes in unparticle physics

We study the virtual effects of unparticle physics in the lepton flavor violating processes $M^0\to l^+l'^-$ and $e^+e^-\to l^+l'^-$ scattering, where $M^0$ denotes the pseudoscalar mesons: $π^0,K_L, D_0,B_0,B_s^0$ and $l,l'$ denote two different lepton flavors. For the decay of $B^0\to l^+l'^-$, there is no constraint from the current experimental upper bounds on the vector unparticle coupling with leptons. The constraint on the coupling constant between scalar unparticle field and leptons is sensitive to the scaling dimension of the unparticle $d_{\cal U}$. For the scattering process $e^-e^+\to l^-l'^+$, there is only constraint from experiments on the vector unparticle couplings with leptons but no constraint on the scalar unparticle. We study the $\sqrt s$ dependence of the cross section $ \frac{1}σ \frac{dσ}{d\sqrt s}$ of $e^+e^-\to l^-l'^+$ with different values of $d_{\cal U}$. If $d_{\cal U}=1.5$, the cross section is independent on the center mass energy. For $d_{\cal U}>1.5$, the cross section increases with $\sqrt s$.

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arXiv2007

Charmless non-leptonic B_s decays to PP, PV and VV final states in the pQCD approach

We calculate the CP-averaged branching ratios and CP-violating asymmetries of a number of two-body charmless hadronic decays $\bar{B_s^0} \to PP, PV, VV$ in the perturbative QCD (pQCD) approach to leading order in $α_s$ (here $P$ and $V$ denote light pseudoscalar and vector mesons, respectively). The mixing-induced CP violation parameters are also calculated for these decays. We also predict the polarization fractions of $B_s \to VV$ decays and find that the transverse polarizations are enhanced in some penguin dominated decays such as $\bar{B_s^0} \to K ^{*}\bar{K^{*}}$, $K ^{*}ρ$. Some of the predictions worked out here can already be confronted with the recently available data from the CDF collaboration on the branching ratios for the decays $ \bar{B_s^0} \to K^+π^-$, $ \bar{B_s^0} \to K^+K^-$ and the CP-asymmetry in the decay $ \bar{B_s^0} \to K^+π^-$, and are found to be in agreement within the current errors. A large number of predictions for the branching ratios, CP-asymmetries and vector-meson polarizations in $\bar{B_s^0}$ decays, presented in this paper and compared with the already existing results in other theoretical frameworks, will be put to stringent experimental tests in forthcoming experiments at Fermilab, LHC and Super B-factories.

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arXiv2007

Exclusive processes $e^+e^-\to VP$ in $k_T$ factorization

The exclusive processes $e^+e^-\to VP$, in the region of which the final state meson momentum is much larger than the hadronic scale $Λ_{QCD}$, are studied in the framework of PQCD approach based on the $k_T$ factorization. Including the transverse momentum distribution in the light cone wave functions, our results are consistent with the experimental measurements. According to our results, many processes have large enough cross sections to be detected at $\sqrt s=10.58$ GeV. The $s$ dependence of the cross section has been directly studied and our result indicates that the $1/s^3$ scaling is more favored than $1/s^4$. We also find that the gluonic contribution for the processes involving $η^{(')}$ is tiny.

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arXiv2007

Lifetime of doubly charmed baryons

In this work, we evaluate the lifetimes of the doubly charmed baryons $Ξ_{cc}^{+}$, $Ξ_{cc}^{++}$ and $Ω_{cc}^{+}$. We carefully calculate the non-spectator contributions at the quark level where the Cabibbo-suppressed diagrams are also included. The hadronic matrix elements are evaluated in the simple non-relativistic harmonic oscillator model. Our numerical results are generally consistent with that obtained by other authors who used the diquark model. However, all the theoretical predictions on the lifetimes are one order larger than the upper limit set by the recent SELEX measurement. This discrepancy would be clarified by the future experiment, if more accurate experiment still confirms the value of the SELEX collaboration, there must be some unknown mechanism to be explored.

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arXiv2007

Twist-3 distribution amplitudes of scalar mesons from QCD sum rules

We study the twist-3 distribution amplitudes for scalar mesons made up of two valence quarks based on QCD sum rules. By choosing the proper correlation functions, we derive the moments of the scalar mesons up to the first two order. Making use of these moments, we then calculate the first two Gegenbauer coefficients for twist-3 distribution amplitudes of scalar mesons. It is found that the second Gegenbauer coefficients of scalar density twist-3 distribution amplitudes for $K^{*}_0$ and $f_0$ mesons are quite close to that for $a_0$, which indicates that the SU(3) symmetry breaking effect is tiny here. However, this effect could not be neglected for the forth Gegenbauer coefficients of scalar twist-3 distribution amplitudes between $a_0$ and $f_0$. Besides, we also observe that the first two Gegenbauer coefficients corresponding to the tensor current twist-3 distribution amplitudes for all the $a_0$, $K^{*}_0$ and $f_0$ are very small. The renormalization group evolution of condensates, quark masses, decay constants and moments are considered in our calculations. As a byproduct, it is found that the masses for isospin I=1, ${1 \over 2}$ scalar mesons are around $1.27 \sim 1.41$ GeV and $1.44 \sim 1.56$ GeV respectively, while the mass for isospin state composed of $\bar{s} s$ is $1.62 \sim 1.73$ GeV.

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arXiv2007

Diquarks and the Semi-Leptonic Decay of $Λ_{b}$ in the Hybrid Scheme

In this work we use the heavy-quark-light-diquark picture to study the semileptonic decay $Λ_b \to Λ_c+l+\barν_l$ in the so-called hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for larger $q^2$ (corresponding to small recoil), which is the invariant mass square of $l+\barν$, whereas the perturbative QCD approach for smaller $q^2$ to calculate the form factors. The turning point where we require the form factors derived in the two approaches to be connected, is chosen near $ρ_{cut}=1.1$. It is noted that the kinematic parameter $ρ$ which is usually adopted in the perturbative QCD approach, is in fact exactly the same as the recoil factor $ω=v\cdot v'$ used in HQET where $v$, $v'$ are the four velocities of $Λ_b$ and $Λ_c$ respectively. We find that the final result is not much sensitive to the choice, so that it is relatively reliable. Moreover, we apply a proper numerical program within a small range around $ρ_{cut}$ to make the connection sufficiently smooth and we parameterize the form factor by fitting the curve gained in the hybrid scheme. The expression and involved parameters can be compared with the ones gained by fitting the experimental data. In this scheme the end-point singularities do not appear at all. The calculated value is satisfactorily consistent with the data which is recently measured by the DELPHI collaboration within two standard deviations.

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arXiv2006

Calculation of the Branching Ratio of $B^{-}\to h_{c}+K^{-}$ in PQCD

The branching ratio of $B^-\to h_c+K^-$ is re-evaluated in the PQCD approach. In this theoretical framework all the phenomenological parameters in the wavefunctions and Sudakov factor are priori fixed by fitting other experimental data, and in the whole numerical computations we do not introduce any new parameter. Our results are consistent with the upper bounds set by the Babar and Belle measurements.

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arXiv2006

Calculation of BR($\bar{B}^0\to Λ_{c}^++\bar p)$ in the PQCD Approach

We calculate the branching ratio of $\bar{B}^0 \to Λ_c^+ \bar{p}$ in the PQCD approach. Most previous model calculations obtained branching ratios significantly larger than experimental data. We find that the predicted branching ratio for BR$(\bar{B}^0 \to Λ_c^+ \bar{p})$ in the PQCD approach can vary over a range of $(2.3\sim 5.1)\times 10^{-5}$ with the largest uncertainty coming from the parameters in the wave function of $Λ_c$. With the favored values for the parameters in the $Λ_c^+$ wave function, $β= 1$ GeV and $m_q = 0.3$ GeV, the branching ratio is about $2.3\times 10^{-5}$ which is satisfactorily consistent with the value measured by experiments.

hep-ph↗

arXiv2006

PQCD Calculation for $Λ_{b}\to Λγ$ in the Standard Model

We calculate the branching ratio of $Λ_b \to Λγ$ in the standard model using the PQCD method. The predicted branching ratio $B(Λ_b \to Λγ)$ is about $(4.3\sim 8.6)\times 10^{-8}$, with reasonable parameter ranges in the heavy baryon distribution amplitude. This branching ratio is much smaller than those obtained in other hadronic model calculations. Future experimental data can provide important information on applicability of the PQCD method to heavy baryon radiative decay.

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