arXiv subjects

Yue-Long Shen

Publications and source records attributed to Yue-Long Shen.

At least 55 records · Page 3Linked to original sources

arXiv2013

Resummation of rapidity logarithms in $B$ meson wave functions

We construct an evolution equation for the $B$ meson wave functions in the $k_T$ factorization theorem, whose solutions sum the double logarithms associated with the light-cone singularities, namely, the rapidity logarithms. The derivation is subtler than that of the Sudakov resummation for an energetic light hadron, due to the involvement of the effective heavy-quark field. The renormalization-group evolution in the factorization scale needs to be included in order to derive an ultraviolet-finite and scale-invariant kernel for resumming the rapidity logarithms. It is observed that this kernel is similar to that of the joint resummation for QCD processes in extreme kinematic regions, which combines the threshold and $k_T$ resummations. We show that the resummation effect maintains the normalization of the $B$ meson wave functions, and strengths their convergent behavior at small spectator momentum. The resummation improved $B$ meson wave functions are then employed in the leading-order analysis of the $B\toπ$ transition form factors, which lead to approximately 25% deduction in the large recoil region.

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arXiv2012

Charmed Scalar Meson Production in $B$ Decays

The study on the charmed scalar meson spectroscopy has become a hot topic both experimentally and theoretically. The $B_{(s)}$ decays provide an ideal place to study their property. We employ the $B$-meson light-cone sum rules to compute the $\bar B_s^0\to D_s^{*+}(2317)$ and $B^-\to D_0^{*0}(2400)$ transition form factors at large recoil, assuming $D_s^{*+}(2317)$ and $D_0^{*0}(2400)$ being scalar quark-anti-quark states. The results are extrapolated to the whole momentum region with the help of HQET. Considering large uncertainties, our results can be consistent with the previous studies, while the power corrections should be large. We also estimate the semi-leptonic decays $\bar B_s^0\to D_s^{*+}(2317)l \barν_l$ and $B^-\to D_0^{*0}(2400)l \barν_l$. The branching fraction of the semi-leptonic $\bar B_s^0\to D_s^{*+}(2317)l \barν_l$ decay is around $6\times 10^{-3} $ for light leptons and $0.8\times 10^{-3} $ for tau final state. The predicted branching ration of $B^-\to D_0^{*0}(2400)l \barν_l$ is slightly larger than $\bar B_s^0\to D_s^{*+}(2317)l \barν_l$, and we hope the future data in LHCb can test these results.

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arXiv2012

Next-to-leading-order corrections to $B \to π$ form factors in $k_T$ factorization

We calculate next-to-leading-order (NLO) corrections to the $B\toπ$ transition form factors at leading twist in the $k_T$ factorization theorem. Light partons off-shell by $k_T^2$ are considered in the quark diagrams, in the effective diagrams for the $B$ meson wave function defined with the effective heavy-quark field, and in the effective diagrams for the pion wave function. It is explicitly demonstrated that the infrared logarithms $\ln k_T^2$ cancel between the above sets of diagrams, as deriving the $k_T$-dependent NLO hard kernel from their difference. The infrared finiteness of the hard kernel confirms the application of the $k_T$ factorization theorem to $B$ meson semileptonic decays. The NLO pion wave function is identical to those constructed from the pion transition and electromagnetic form factors, consistent with its universality. Choosing the renormalization and factorization scales lower than the $B$ meson mass, the NLO corrections are under control: they amount only up to 30% of the form factors at large recoil of the pion, when varying models for the meson wave functions.

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arXiv2011

Next-to-leading-order correction to pion form factor in $k_T$ factorization

We calculate next-to-leading-order (NLO) correction to the pion electromagnetic form factor at leading twist in the $k_T$ factorization theorem. Partons off-shell by $k_T^2$ are considered in both quark diagrams and effective diagrams for the transverse-momentum-dependent (TMD) pion wave function. The light-cone singularities in the TMD pion wave function are regularized by rotating the Wilson lines away from the light cone. The soft divergences from gluon exchanges among initial- and final-state partons cancel exactly. We derive the infrared-finite $k_T$-dependent NLO hard kernel for the pion electromagnetic form factor by taking the difference of the above two sets of diagrams. Varying the renormalization and factorization scales, we find that the NLO correction is smaller, when both the scales are set to the invariant masses of internal particles: it becomes lower than 40% of the leading-order (LO) contribution for momentum transfer squared $Q^2>7$ GeV$^2$. It is observed that the NLO leading-twist correction does not play an essential role in explaining the experimental data, but the LO higher-twist contribution does.

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arXiv2010

$B$-to-Glueball form factor and Glueball production in $B$ decays

We investigate transition form factors of $B$ meson decays into a scalar glueball in the light-cone formalism. Compared with form factors of $B$ to ordinary scalar mesons, the $B$-to-glueball form factors have the same power in the expansion of $1/m_B$. Taking into account the leading twist light-cone distribution amplitude, we find that they are numerically smaller than those form factors of $B$ to ordinary scalar mesons. Semileptonic $B\to Gl\barν$, $B\to Gl^+l^-$ and $B_s\to Gl^+l^-$ decays are subsequently investigated. We also analyze the production rates of scalar mesons in semileptonic $B$ decays in the presence of mixing between scalar $\bar qq$ and glueball states. The glueball production in $B_c$ meson decays is also investigated and the LHCb experiment may discover this channel. The sizable branching fraction in $B_c\to (π^+π^-)l^-\barν$, $B_c\to (K^+K^-)l^-\barν$ or $B_c\to (π^+π^-π^+π^-)l^-\barν$ could be a clear signal for a scalar glueball state.

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arXiv2010

Space- and time-like electromagnetic pion form factors in light-cone pQCD

We present a combined analysis of the space- and time-like electromagnetic pion form factors in light-cone perturbative QCD with transverse momentum dependence and Sudakov suppression. Including the non-perturbative ``soft' QCD and power suppressed twist-3 corrections to the standard twist-2 perturbative QCD result, the experimental pion data available at moderate energies/momentum transfers can be explained reasonably well. This may help towards resolving the bulk of the existing discrepancy between the space- and time-like experimental data.

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arXiv2010

$|V_{ub}|$ and $B\toη^{(')}$ Form Factors in Covariant Light Front Approach

$B\to (π, η, η')$ transition form factors are investigated in the covariant light-front approach. With theoretical uncertainties, we find that $B\to (π, η, η')$ form factors at $q^2=0$ are $f^{(π, η, η')}_{+}(0)=(0.245^{+0.000}_{-0.001}\pm 0.011, 0.220 \pm 0.009\pm0.009, 0.180\pm 0.008^{+0.008}_{-0.007})$ for vector current and $f^{(π, η, η')}_{T}(0)=(0.239^{+0.002+0.020}_{-0.003-0.018}, 0.211\pm 0.009^{+0.017}_{-0.015}, 0.173\pm 0.007^{+0.014}_{-0.013})$ for tensor current, respectively. With the obtained $q^2$-dependent $f^π_{+}(q^2)$ and observed branching ratio (BR) for $\bar B_d\to π^+ \ell \bar ν_{\ell}$, the $V_{ub}$ is found as $|V_{ub}|_{LF}= (3.99 \pm 0.13)\times 10^{-3}$. As a result, the predicted BRs for $\bar B\to (η, η') \ell \barν_{\ell}$ decays with $\ell=e,μ$ are given by $(0.49^{+0.02+0.10}_{-0.04- 0.07}, 0.24^{+0.01+0.04}_{-0.02-0.03})\times 10^{-4}$, while the BRs for $D^-\to (η,η')\ell\barν_{\ell}$ are $(11.1^{+0.5+0.9}_{-0.6-0.9}, 1.79^{+0.07+0.12}_{-0.08-0.12})\times 10^{-4}$. In addition, we also study the integrated lepton angular asymmetries for $\bar B\to (π,η,η')τ\barν_τ$:$(0.277^{+0.001+0.005}_{-0.001-0.007},0.290^{+0.002+0.003}_{-0.000-0.003},0.312^{+0.004+0.005}_{-0.000-0.006})$.

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arXiv2009

The Clean Way to Identify a Scalar Glueball

The existence of a glueball has been a tough work for many years study. Utilizing the well developed QCD theory for $B$ meson decays, we propose a new way to identify whether a scalar glueball existed or not. In the presence of mixing between glueballs and ordinary scalar mesons, we explore the possibility to extract the mixing parameters from semileptonic B decays and nonleptonic B decays. We also point out a clean way to identify a glueball through $B_c$ decays.

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arXiv2009

$Λ_b \to p, Λ$ transition form factors from QCD light-cone sum rules

Light-cone sum rules for the $Λ_b \to p, Λ$ transition form factors are derived from the correlation functions expanded by the twist of the distribution amplitudes of $Λ_b$ baryon. In terms of the $Λ_b$ three-quark distribution amplitudes models constrained by the QCD theory, we calculate the form factors at small momentum transfers and compare the results with that estimated in the conventional light-cone sum rules (LCSR) and perturbative QCD approaches. Our results indicate that the two different version of sum rules can lead to the consistent numbers of form factors responsible for $Λ_b \to p$ transition. The $Λ_b \to Λ$ transition form factors from LCSR with the asymptotic $Λ$ baryon distribution amplitudes are found to be almost one order larger than that obtained in the $Λ_b$-baryon LCSR, implying that the pre-asymptotic corrections to the baryonic distribution amplitudes are of great importance. Moreover, SU(3) symmetry breaking effect between the form factors $f_1^{Λ_b \to p}$ and $f_1^{Λ_b \to Λ}$ are computed as $28^{+14}_{-8} %$ in the framework of $Λ_b$-baryon LCSR.

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arXiv2009

Covariant Light-Front Approach for $B_c$ transition form factors

In the covariant light-front quark model, we investigate the form factors of $B_c$ decays into $D, D^*, D_s, D_s^*, η_c, J/ψ, B, B^*, B_s, B_s^*$ mesons. The form factors in the spacelike region $q^2<0$ are directly evaluated. To extrapolate the form factors to the full kinematic region, we fit the form factors by adopting a three-parameter form from the spacelike region. $b\to u,d,s$ transition form factors at maximally recoiling point ($q^2=0$) are smaller than $b\to c$ and $c\to d,s$ transition form factors, while the $b\to d,s,c$ form factors at zero recoiling point are close to each other. In the fitting procedure, we find the parameters for the form factors $A_2(B_c\to B^*)$ and $A_2(B_c\to B^*_s)$ strongly depend on the decay constants of $B^*$ and $B_s^*$ mesons. Fortunately, the semileptonic and nonleptonic $B_c$ decays are not sensitive to these form factors. With the form factors, we also investigate the branching fractions, polarizations of the semileptonic $B_c\to Mlν$ decays. Semileptonic $B_c\to (η_c,J/ψ)lν$ and $B_c\to (B_s,B_s^*)lν$ decays have much larger branching fractions than $B_c\to (D,D^*,B,B^*)lν$. In the three kinds of $B_c\to Vlν$ decays, contributions from the longitudinal polarized vector is comparable with those from the transversely polarized vector. These predictions will be tested at the ongoing and forthcoming hadron colliders.

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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

Study of $K^_0(1430)$ and $a_0(980)$ from $B\to K^_0(1430)π$ and $B\to a_0(980)K$ Decays

We use the decay modes $B \to K^*_0(1430) π$ and $B \to a_0(980) K$ to study the scalar mesons $K^*_0(1430)$ and $a_0(980)$ within perturbative QCD framework. For $B \to K^*_0(1430) π$, we perform our calculation in two scenarios of the scalar meson spectrum. The results indicate that scenario II is more favored by experimental data than scenario I. The important contribution from annihilation diagrams can enhance the branching ratios about 50% in scenario I, and about 30% in scenario II. The predicted branching ratio of $B \to a_0(980) K$ in scenario I is also less favored by the experiments. The direct CP asymmetries in $B \to K^*_0(1430) π$ are small, which are consistent with the present experiments.

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arXiv2007

The study of $B_c^- \to X(3872)π^-(K^-)$ Decays in the Covariant Light-Front Approach

In the covariant light-front quark model, we calculate the form factors of $B_c^-\to J/ψ$ and $B_c^-\to X(3872)$. Since the factorization of the exclusive processes $B_c^- \to J/ψπ^-(K^-)$ and $B_c^- \to X(3872)π^-(K^-)$ can be proved in the soft-collinear effective theory, we can get the branching ratios for these decays easily from the form factors. Taking the uncertainties into account, our results for the branching ratio of $B_c^-\to J/ψπ^-(K^-)$ are consistent with the previous studies. By identifying X(3872) as a $1^{++}$ charmonium state, we obtain ${\cal BR}(B_c^-\to X(3872)π^-)=(1.7^{+0.7+0.1+0.4}_{-0.6-0.2-0.4}) \times 10^{-4}$ and ${\cal BR}(B_c^-\to X(3872)K^-)=(1.3^{+0.5+0.1+0.3}_{-0.5-0.2-0.3})\times 10^{-5}$. If assuming X(3872) as a $1^{--}$ state, the branching ratios will be one order magnitude larger than those of $1^{++}$ state. These results can be easily used to test the charmonium description for this mysterious meson X(3872) at LHCb experiment.

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arXiv2006

Study of scalar mesons f_0(980) and f_0(1500) from $B \to f_0(980) K$ and $B \to f_0(1500) K$ Decays

Within perturbative QCD approach based on $k_T$ factorization, we analyze the scalar mesons $f_0(980)$ and $f_0(1500)$ productions in B decays. By identifying $f_0(980)$ as the composition of $\bar ss$ and $\bar nn=(\bar uu+\bar dd)/\sqrt2$, we calculate the exclusive decays $B\to f_0(980) K$. We find that the non-factorization $f_0$-emission diagrams can give larger contribution to the branching ratio, than the previous PQCD calculation. Our new results can explain the current experimental data well. Under the assumption of quarkonium dominance, we study the branching ratio of decays $B\to f_0(1500) K$. The results show that in the two-quark picture of $f_0$ meson the contribution from $\bar s s$ component is at the similar size as that from the $\bar n n$ component. Comparing with the data, our results show the preference of $f_0(1500)$ as a member of the ground state of scalar $\bar qq$ nonet. Similar results can also apply to $f_0(1370)$ and $f_0(1710)$, if these mesons are dominated by the quarkonium content. With more experimental data in future, these studies will help us understand the intrinsic characters of these scalar mesons.

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arXiv2006

Role of electromagnetic dipole operator in the electroweak penguin dominated vector meson decays of $B$ meson

The pure annihilation type decays $B^0_d\toϕγ$ and $B_s\toργ$ receive only color suppressed penguin contributions with a very small branching ratio in the standard model. When we include the previously neglected electromagnetic dipole operator, the branching ratios can be enhanced one order magnitude larger than previous study using QCD factorization approach. That is ${\cal BR}(\bar B^0_d\toϕγ)\simeq 1 \times 10^{-11}$ and ${\cal BR}(B_s\toργ) \sim (6-16)\times 10^{-10}$. The new effect can also give a large contribution, of order $10^{-9}$, to transverse polarization of $B\toϕρ$ and $B\to ωϕ$ which is comparable to the longitudinal part. These effects can be detected in the LHCb experiment and the Super-B factories.

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arXiv2006

Final State Interaction In $B\to KK$ Decays

We study the final state interaction effects in $B\to KK$ decays. We find that the $t$ channel one-particle-exchange diagrams cannot enhance the branching ratios of $\bar{B^0}\to K^0\bar{K^0}$ and $B^-\to K^0K^-$ very sizably. For the pure annihilation process $\bar{B^0}\to K^+K^-$, the obtained branching ratio by final state interaction is at ${\cal{O}}(10^{-8})$.

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arXiv2006

Study of $B\to K^* ρ, K^*ω$ Decays with Polarization in Perturbative QCD Approach

The $B \to K^{*}ρ$, $ K^{*}ω$ decays are useful to determine the CKM angle $ϕ_3=γ$. Their polarization fractions are also interesting since the polarization puzzle of the $B\to ϕK^*$ decay. We study these decays in the perturbative QCD approach based on $k_T$ factorization. After calculating of the non-factorizable and annihilation type contributions, in addition to the conventional factorizable contributions, we find that the contributions from the annihilation diagrams are crucial. They give dominant contribution to the strong phases and suppress the longitudinal polarizations. Our results agree with the current existing data. We also predict a sizable direct CP asymmetries in $B^+ \to K^{*+}ρ^0$, $B^0 \to K^{*+}ρ^-$, and $B^+ \to K^{*+}ω$ decays, which can be tested by the oncoming measurements in the B factory experiments.

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arXiv2005

B_s \to ρ(ω) K^* with Perturbative QCD approach

$B_s \to ρ(ω) K^{\ast}$ are useful to determine the $B_s$ distribution amplitude, as well as constrain the CKM phase angle $α$. We study these decays within the Perturbative QCD (PQCD) picture. In this approach, we calculate factorizable, non-factorizable, as well as annihilation diagrams. We find the branching ratio for $B_s \to ρ^+ K^{*-}$ is big to order $10^{-5}$, we also find there's large direct CP violation in $B_s(\bar B_s) \to ρ^0(ω) \bar K^{*0}(K^{*0})$. Our predictions are consistent with those from other methods and current experiments.

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