arXiv subjects

Guo-Li Wang

Publications and source records attributed to Guo-Li Wang.

At least 91 records · Page 5Linked to original sources

arXiv2016

Weak Decays of $J/ψ$ and $Υ(1S)$

In this paper we study the weak decays of $J/ψ$ and $Υ(1S)$. Using the Bethe-Salpeter method, we calculate the hadronic transition amplitude and give the form factors. We find that two new form factors $h_1$ and $h_2$, which do not appear in existing literature, have contributions in $1^-\to 1^-$ decays. They affect the branching ratios of semi-leptonic and non-leptonic decays by the rate of $3\%\sim6\%$ and $2\%\sim14\%$, respectively, so their contributions can not be ignored and should be considered. Our results show that, for the semi-leptonic decay modes, the largest branching ratios are of the order of $10^{-10}$ both for $J/ψ$ and $Υ(1S)$ decays, and the largest branching ratios of non-leptonic decays are of the order of $10^{-9}$ for $J/ψ$ and $10^{-10}$ for $Υ(1S)$.

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arXiv2016

$D$-Wave Charmonia $η_{c2}$($1{^1D_2}$), $ψ_2$($1{^3D_2}$), and $ψ_3$($1{^3D_3}$) in $B_c$ Decays

We study the semi-leptonic and non-leptonic decays of $B_c$ meson to $D$-wave charmonia, namely, $η_{c2}(1^1\!D_2)$, $ψ_2(1^3\!D_2)$, and $ψ_3(1^3\!D_3)$. In our calculations, the instantaneous Bethe-Salpeter method is applied to achieve the hadronic matrix elements. This method includes relativistic corrections which are important especially for the higher orbital excited states. For the semi-leptonic decay channels with electron as the final lepton, we get the branching ratios $\mathcal{B}[B_c \rightarrow η_{c2}e\barν_e] = 5.9^{-0.8}_{+1.0}\times 10^{-4}$, $\mathcal{B}[B_c \rightarrow ψ_2e\barν_e]=1.5^{-0.2}_{+0.3}\times 10^{-4}$, and $\mathcal{B}[B_c \rightarrow ψ_3e\barν_e]=3.5^{-0.6}_{+0.8}\times 10^{-4}$. The transition form factors, forward-backward asymmetries, and lepton spectra in these processes are also presented. For the non-leptonic decay channels, those with $ρ$ as the lighter meson have the largest branching ratios, $\mathcal{B}[B_c \rightarrow η_{c2}ρ] = 8.1^{-1.0}_{+1.0}\times 10^{-4}$, $\mathcal{B}[B_c \rightarrow ψ_2ρ]=9.6^{-1.0}_{+1.0}\times 10^{-5}$, and $\mathcal{B}[B_c \rightarrow ψ_3ρ]=4.1^{-0.7}_{+0.8}\times 10^{-4}$.

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arXiv2016

Rare radiative decays of the $B_c$ meson

In this paper, we study the rare radiative processes $B_c\to D_{sJ} ^{(*)}γ$ within the Standard Model, where $D_{sJ}^{(*)}$ stands for the meson $D_s^*$,~$D_{s1}(2460,2536)$ or ~$D_{s2}^*(2573)$. During the investigations, we consider the contributions from the penguin, annihilation, color-suppressed and color-favored cascade diagrams. Our results show that: 1) the penguin and annihilation contributions are dominant in the branching fractions; 2) for the processes $B_c\to D_s^{*}γ$ and $B_c\to D_{s1}(2460,2536)γ$, the effects from the color-suppressed and color-favored cascade diagrams are un-negligible.

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arXiv2015

Some of semileptonic and nonleptonic decays of $B_c$ meson in a Bethe-Salpeter relativistic quark model

The semileptonic decays $B_c^+\rightarrow P(V) +\ell^++\barν_\ell$ and the nonleptonic decays $B_c^+\rightarrow P(V)+L$, where $P(V)$ denotes a pseudoscalar (vector) charmonium or ($\bar{b}s$)-meson, and $L$ denotes a light meson, are studied in the framework of improved instantaneous Bethe-Salpeter (BS) equation and the Mandelstam formula. The numerical results (width and branching ratio of the decays) are presented in tables, and in order to compare conveniently, those obtained by other approaches are also put in the relevant tables. Based on the fact that the ratio $\frac{\mathcal{BR}(B_c^+\rightarrowψ(2S)π^+)}{\mathcal{BR}(B_c^+\rightarrow J/ψπ^+)}=0.24^{+0.023}_{-0.040}$ estimated here is in good agreement with the observation by the LHCb $\frac{\mathcal{BR}(B_c^+\rightarrow ψ(2S)π^+)}{\mathcal{BR}(B_c^+\rightarrow J/ψπ^+)}=0.250\pm0.068(\mathrm{stat})\pm0.014(\mathrm{syst})\pm0.006(\mathcal{B})$, one may conclude that with respect to the decays the present framework works quite well.

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arXiv2015

The nonleptonic charmless decays of $B_c$ meson

In this paper, with the framework of (p)NRQCD and SCET, the processes $B_c\to M_1 M_2$ are investigated. Here $M_{1(2)}$ denotes the light charmless meson, such as $π$, $ρ$, $K$ or $K^*$. Based on the SCET power counting rules, the leading transition amplitudes are picked out, which include $A_{wA}^2$, $A_{wB}^2$, $A_{wC}^2$, $A_{wD}^2$ and $A_{c}^0$. From SCET, their factorization formulae are proven. Based on the obtained factorization formulae, in particular, the numerical calculation on $A_{wB}^2$ is performed.

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arXiv2015

The Electromagnetic Decays of $B^{\pm}_c(2S)$

We calculate the electromagnetic (EM) decay widths of the $B^{\pm}_c(2S)$ meson, which is observed recently by the ATLAS Collaboration. The main EM decay channels of this particle are $1{^3S_1}γ$ and $1{P}γ$, which, in literature, are estimated to have the branching ratio of about $1/10$. In this work, we get the partial decay widths: $Γ(2{^1S_0}\rightarrow 1{^3S_1}γ)=0.192$ keV, $Γ(2{^1S_0}\rightarrow 1{P_1}γ) = 2.24$ keV and $Γ(2{^1S_0}\rightarrow 1{P_1^\prime}γ) = 11.4$ keV. In the calculation, the instantaneous approximated Bethe-Salpeter method is used. For the $P$-wave $B_c$ mesons, the wave functions are given by mixing the $^3P_1$ and $^1P_1$ states. Within the Mandelstam formalism, the decay amplitude is given, which includes the relativistic corrections.

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arXiv2015

The rare semi-leptonic $B_c$ decays involving orbitally excited final mesons

The rare processes $B_c\to D_{(s)J} ^{(*)}μ\barμ$, where $D_{(s)J}^{(*)}$ stands for the final meson $D_{s0}^*(2317)$, $D_{s1}(2460,2536)$,~$D_{s2}^*(2573)$, $D_0^*(2400)$, $D_{1}(2420,2430)$ or~$D_{2}^*(2460)$, are studied within the Standard Model. The hadronic matrix elements are evaluated in the Bethe-Salpeter approach and furthermore a discussion on the gauge-invariant condition of the annihilation hadronic currents is presented. Considering the penguin, box, annihilation, color-favored cascade and color-suppressed cascade contributions, the observables $\text{d}Br/\text{d}Q^2$, $A_{LPL}$, $A_{FB}$ and $P_L$ are calculated.

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arXiv2014

The Study of Rare $B_c\rightarrow D^{(*)}_{s,d}l\bar{l}$ Decays

In this paper, we study rare decays $B_c\rightarrow D^{(*)}_{s,d}l\bar{l}$ within the Standard Model. The penguin, box, annihilation, color-favored cascade and color-suppressed cascade contributions are included. Based on our calculation, the annihilation and color-favored cascade diagrams play important roles in the differential branching fractions, forward-backward asymmetries, longitudinal polarizations of the final vector mesons and leptonic longitudinal polarization asymmetries. More importantly, color-favored cascade decays largely enhance the resonance cascade contributions. To avoid the resonance cascade contribution pollution, new cutting regions are put forward.

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arXiv2013

Why X(3915) is so narrow as a $χ_{c0}(2P)$ state

New resonance X(3915) was identified as the charmonium $χ_{c0}(2P)$ by BABAR Collaboration, but there seems still open question of this assignment: why its full width is so narrow? To answer this question, we calculate the Okubo-Zweig-Iizuka (OZI) allowed strong decays $X(3915)\to D \bar D$, where X(3915) is assigned as a $χ_{c0}(2P)$ state, and estimate its full width in the cooperating framework of $^3/!P_0^{}$ model and the Bethe-Salpeter (BS) method using the Mandelstam Formalism, during which non-perturbative QCD effects of the hadronic matrix elements are well considered by overlapping integral over the relativistic Salpeter wave functions of the initial and finial states. We find the node structure of $χ_{c0}(2P)$ wave function resulting in the narrow width of X(3915) and show the dependence of the decay width on the variation of the initial mass of X(3915). We point out that the rate of $\frac{Γ(X(3915)\to D^+ D^-)}{Γ(X(3915)\to D^0 \bar D^0)}$ is crucial to confirm whether X(3915) is the $χ_{c0}(2P)$ state or not.

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arXiv2013

Lepton-number violating four-body decays of heavy mesons

Neutrinoless hadron Lepton Number Violating (LNV) decays can be induced by virtual Majorana neutrino, which in turn indubitably show the Majorana nature of neutrinos. Many three-body LNV processes and Lepton Flavour Violating (LFV) processes have been studied extensively in theory and by experiment. As a supplement, we here study 75 four-body LNV (LFV) processes from heavy pseudoscalar $B$ and $D$ decays. Most of these processes have not been studied in theory and searched for in experiment, while they may have sizable decay rates. Since the four-body decay modes have the same vertexes and mixing parameters with three-body cases, so their branching fractions are comparable with the corresponding three-body decays. We calculate their decay widths and branching fractions with current bounds on heavy Majorana neutrino mixing parameters, and estimate some channels' reconstruction events using the current experimental data from Belle.

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arXiv2013

Two-Body Strong Decay of Z(3930) as the $χ_{c2} (2P)$ State

The new particle Z(3930) found by the Belle and BaBar Collaborations through the $γγ\rightarrow D\bar D$ process is identified to be the $χ_{c2}(2P)$ state. Since the mass of this particle is above the $D\bar D^{(\ast)}$ threshold, the OZI-allowed two-body strong decays are the main decay modes. In this paper, these strong decay modes are studied with two methods. One is the instantaneous Bethe-Salpeter method within Mandelstam formalism. The other is the combination of the $^3P_0$ model and the former formalism. The total decay widths are 26.3 and 27.3 MeV for the methods with or without the $^3P_0$ vertex, respectively. The ratio of $Γ_{D\bar D}$ over $Γ_{D\bar D^\ast}$ which changes along with the mass of the initial meson is also presented.

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arXiv2013

The Properties of $D^{*}_{s1}(2700)^{+}$

The new particle $D^{*}_{s1}(2700)^{+}$ has stimulated many attentions. There are different assignments of its inherent properties. It may be a $2^3S_1$, $1^3D_1$ or the mixture of $2^3S_1-1^3D_1$ $c\bar s$ $1^-$ state. By considering its mass, decay modes, full width, production rate, and comparing with current experimental data, we point out that there is another more reasonable assignment: $D^{*}_{s1}(2700)^{+}$ could be identified as two resonances, one of which is a $2^3S_1$ state, another is a 1D state, and both are $c\bar s$ $1^-$ states. The two states have very close masses, which are around 2700 MeV, and both have broad decay widths. So in experiments, the overlapping of $DK$ or $D^*K$ invariant mass distribution coming from their decays is found, but the current experiments could not distinguish these two resonances and reported one particle.

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arXiv2013

Annihilation rate of $2^{-+}$ charmonium and bottomonium

The $1^1D_2 (c\bar c)$ state is the ground state of spin-singlet D-wave charmonia. Although it has not been found yet, the experimental data accumulate rapidly. This charmonium attracts more and more attention, especially when the BaBar Collaboration finds that the X(3872) particle has negative parity. In this paper we calculate the double-gamma and double-gluon annihilation processes of $^1D_2$ charmonia and bottomonia by using the instantaneous Bethe-Salpeter method. We find the relativistic corrections make the decay widths of $1^1D_2 (c\bar c)$ 2$\sim$5 times smaller than the non-relativistic results. If this state is below the $D^0{D^{0}}^\ast$ threshold, we can use the sum of annihilation widths and EM transition widths to estimate the total decay width. Our result for $1{^1D_2} (c\bar c)$ with $m=3820$ GeV is $Γ= 432$ keV. The dominant decay channel $1^1D_2 (c\bar c)\to h_c γ$, whose branching ratio is about 90%, can be used to discover this state.

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arXiv2012

EM Decay of X(3872) as the $1{^1D_2}(2^{-+})$ charmonium

The recently BaBar results raise the possibility that X(3872) has negative parity. This makes people reconsider assigning X(3872) to the $1{^1D_2}(c\bar c)$ state. In this paper we give a general form of the wave function of $2^{-+}$ mesons. By solving the instantaneous Bethe-Salpeter equation, we get the mass spectrum and corresponding wave functions. We calculate electromagnetic decay widths of the first $2^{-+}$ state which we assume to be the X(3872) particle. The results are $Γ(2^{-+}(3872)\rightarrow J/ψγ) = 1.59^{+0.53}_{-0.42}$ keV, $Γ(2^{-+}(3872)\rightarrow ψ(2S)γ) = 2.87^{+1.46}_{-0.97}$ eV and $Γ(2^{-+}(3872)\rightarrow ψ(3770)γ) = 0.135^{+0.066}_{-0.047}$ keV. The ratio of branch fractions of the second and first channel is about 0.002, which is inconsistent with the experimental value $3.4\pm 1.4$. So X(3872) is unlikely to be a $2^{-+}$ charmonium state. In addition, we obtain a relatively large decay width for $2^{-+}(3872)\rightarrow h_cγ$ channel which is $392^{+62}_{-111}$ keV.

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arXiv2012

The Productions and Strong Decays of $D_q(2S)$ and $B_q(2S)$

We study the productions of first radial excited states $D_q(2S)$ ($q=u, d, s$) and $B_q(2S)$ in exclusive semi-leptonic $B_{q'}$ ($q'=u, d s, c$) decays by the improved Bethe-Salpeter method. These 2S states can be detected through their strong decays to ground mesons, where the strong decays are calculated by the low energy approximation as well as the impulse approximation. Some channels have ratios of order $10^{-4}$: $Br(B^+\to\bar D^0(2S)\ell^+{ν_\ell})\times Br(\bar D^0(2S)\to \bar D^{*}π)\approx(4.9\pm4.0)\times10^{-4}$, $Br(B^0\to D^-(2S)\ell^+{ν_\ell})\times Br(D^-(2S)\to \bar D^{*}π)\approx(4.4\pm3.4)\times10^{-4}$. These channels could be measured by the current B-factories. For $D_s(2S)$, we also obtain a relative large ratio: $Br(B_s^0\to D_s^-(2S)\ell^+{ν_\ell})\times Br(D_s^-(2S)\to \bar D^{*}\bar K)\approx (9.9\pm14.9)\times10^{-4}$. Although there are discrepancies of the full decay width between the theoretical predictions of ${D}^0(2S)$ and experimental results of $D(2550)^0$, the new detected state $D(2550)^0$ is very likely the ${D}^0(2S)$ state.

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arXiv2012

Estimating Form Factors of $B_s\rightarrow D_s^{(*)}$ and their Applications to Semi-leptonic and Non-leptonic Decays

$B_s^0\rightarrow D_s^{-}$ and $B_s^0\rightarrow D_s^{*-}$ weak transition form factors are estimated for the whole physical region with a method based on an instantaneous approximated Mandelstam formulation of transition matrix elements and the instantaneous Bethe-Salpeter equation. We apply the estimated form factors to branching ratios, CP asymmetries and polarization fractions of non-leptonic decays within the factorization approximation. And we study the non-factorizable effects and annihilation contributions with the perturbative QCD approach. The branching ratios of semi-leptonic $B_s^0\rightarrow D_s^{(*)-}l^+ν_l$ decays are also evaluated. We show that the calculated decay rates agree well with the available experimental data. The longitudinal polarization fraction of $B_s\rightarrow D_s^*V(A)$ decays are $\sim0.8$ when $V(A)$ denotes a light meson, and are $\sim0.5$ when $V(A)$ denotes a $D_q$ ($q=d,s$) meson.

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arXiv2012

Is $Z_b(10610)$ a Molecular State?

Whether molecular states indeed exist in nature has been disputed for a long time. Several new resonances have been observed in the recent experiments and they seem to be of exotic structures and some of them have been proposed to be molecular states. The very recent observation of $Z_b(10610)[(10608.4\pm 2.0)$ MeV] and $Z_b(10650)[(10653.2\pm 1.5)$ MeV] encourages the interpretation of multi-quark states. In the Beter-Salpeter (BS) approach, we study the possibility if two heavy mesons can form a molecular state by exchanging light mesons. Our results indicate that two heavy mesons can form an isospin singlet (I=0) bound state but cannot form an isospin triplet (I=1) when the contribution of $σ-$ exchange is reasonably small, i.e. as the coupling of $σ$ with mesons $g_σ$ takes the value given in previous literatures. Thus we conclude that the newly observed $Z_b(10610)$ should not be a molecular state, but a tetraquark state instead, at most, the fraction of the molecular state in the physical resonance $Z_b(10610)$ is tiny.

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arXiv2012

The Strong Decays of Orbitally Excited $B^{*}_{sJ}$ Mesons by Improved Bethe-Salpeter Method

We calculate the masses and the strong decays of orbitally excited states $B_{s0}$, $B'_{s1}$, $B_{s1}$ and $B_{s2}$ by the improved Bethe-Salpeter method. The predicted masses of $B_{s0}$ and $B'_{s1}$ are $M_{B_{s0}}=5.723\pm0.280 {\rm GeV}$, $M_{B'_{s1}}=5.774\pm0.330 {\rm GeV}$. We calculate the isospin symmetry violating decay processes $B_{s0}\to B_s π$ and $B'_{s1}\to B_s^* π$ through $π^0-η$ mixing and get small widths. Considering the uncertainties of the masses, for $B_{s0}$ and $B'_{s1}$, we also calculate the OZI allowed decay channels: $B_{s0}\to B\bar K$ and $B'_{s1}\to B^*\bar K$. For $B_{s1}$ and $B_{s2}$, the OZI allowed decay channels $B_{s1}\to B^{*}\bar K$, $B_{s2}\to B\bar K$ and $B_{s2}\to B^{*}\bar K$ are studied. In all the decay channels, the reduction formula, PCAC relation and low energy theorem are used to estimate the decay widths. We also obtain the strong coupling constants $G_{B_{s0}B_sπ}$, $G_{B_{s0}B\bar K}$, $G_{B'_{s1}B_s^*π}$, $F_{B'_{s1}B_s^*π}$, $G_{B'_{s1}B^*\bar K}$, $F_{B'_{s1}B^*\bar K}$, $G_{B_{s1}B^{*}\bar K}$, $F_{B_{s1}B^{*}\bar K}$, $G_{B_{s2}B\bar K}$ and $G_{B_{s2}B^{*}\bar K}$.

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