arXiv subjects

Hong-Wei Ke

Publications and source records attributed to Hong-Wei Ke.

At least 37 records · Page 2Linked to original sources

arXiv2019

Study on $Ξ_{cc}\toΞ_c$ and $Ξ_{cc}\toΞ'_c$ weak decays in the light-front quark model

In this work we study the weak decays of $Ξ_{cc}\toΞ_c$ and $Ξ_{cc}\toΞ'_c$ in the light-front quark model. Generally, a naive, but reasonable conjecture suggests that the $cc$ subsystem in $Ξ_{cc}$ ( $us$ pair in $Ξ^{(')}_c$) stands as a diquark with definite spin and color assignments. During the concerned processes, the diquark of the initial state is not a spectator, and must be broken. A Racah transformation would decompose the original $(cc)q$ into a combination of $c(cq)$ components. Thus we may deal with the decaying $c$ quark alone while keeping the $(cq)$ subsystem as a spectator. With the re-arrangement of the inner structure we calculate the form factors numerically and then obtain the rates of semi-leptonic decays and non-leptonic decays, which will be measured in the future.

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arXiv2019

$Σ_{b}\toΣ_c^*$ weak decays in the light-front quark model with two schemes to deal with the polarization of diquark

Thanks to the remarkable achievements of LHC, a large database on baryons has been accumulated, so it is believed that the time for precisely studying baryons especially heavy baryons, has come. By analyzing the data, the quark-diquark structure which has been under intensive discussions, can be tested. In this work the decay widths of weak transitions $Σ_b\to Σ^*_c+X$ are calculated in terms of the light front quark model (LFQM). To carry out the calculations, the quark-diquark picture is employed where an axial-vector diquark composed of two light quarks serves as a spectator in the concerned processes. The first step of this work is to construct the vertex functions for $Σ^{(*)}_c$ and $Σ_b$, then the relevant form factors are derived. It is shown that under the heavy quark limit the Isgur-Wise functions for the transition are re-deduced. Indeed, how to properly depict the polarization ($ε_μ$) of the diquark is slightly tricky. In this work, we apply two schemes to explicitly determine the momentum-dependence of the diquark. The corresponding numerical results are presented which will be testified by the future experiments.

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arXiv2019

Revisiting $Λ_{b}\toΛ_{c}$ and $Σ_{b}\toΣ_{c}$ weak decays in the light-front quark model

In this work, we study $Λ_{b}\toΛ_{c}$ and $Σ_{b}\toΣ_{c}$ weak decays in the light-front quark model. As is well known, the key point for such calculations is properly evaluating the hadronic transition matrix elements which are dominated by the non-perturbative QCD effect. In our calculation, we employ the light-front quark model and rather than the traditional diquark picture, we account the two spectator light quarks as individual ones. Namely during the transition, they retain their color indices, momenta and spin polarizations unchanged. Definitely, the subsystem composed of the two light quarks is still in a color-anti-triplet and possesses a definite spin, but we do not priori assume the two light quarks to be in a bound system-diquark. Our purpose is probing the diquark picture, via comparing the results with the available data, we test the validity and applicability of the diquark structure which turns a three-body problem into a two-body one, so greatly simplifies the calculation. It is indicated that the two approaches (diquark and a subsystem within which the two light quarks are free) lead to similar numerical results even though the model parameters in the two schemes might deviate slightly. Thus, the diquark approach seems sufficiently reasonable.

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arXiv2018

Estimating the production rates of D-wave charmed mesons via the semileptonic decays of bottom mesons

In this work, using the covariant light front approach with conventional vertex functions, we estimate the production rates of $D$-wave charmed/charmed-strange mesons via $B_{(s)}$ semileptonic decays. Due to these calculated considerable production rates, it is possible to experimentally search for $D$-wave charmed/charmed-strange mesons via the semileptonic decays, which may provide extra approach to explore $D$-wave charmed/charmed-strange mesons.

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arXiv2018

Study on the strong decays of $ϕ(2170)$ and a grand expectation for the future charm-tau factory

The present data imply that $ϕ(2170)$ may not be an excited state of $ϕ$, but is a four quark state with $ss\bar s \bar s$ constituents. Furthermore, there are no two mesons of $s\bar s$ available to form a molecule which fits the mass spectrum of $ϕ(2170)$, thus we suggest it should be an $ss\bar s \bar s$ tetraquark state. In this scenario, we estimate its decay rates through the fall-apart mechanism. Our theoretical estimates indicate that its main decay modes should be $ϕ(2170)$ into $ϕf_0(980)$, $ h_1η$, $ h_1η'$, $K_1(1270)K$ and $K_1(1400)K$. Under this hypothesis the modes $ϕ(2170)\to K^*(890)^0\bar K^*(890)^0$, $K^+K^-$ and $K^0_LK^0_S$ should be relatively suppressed. Since the width of $h_1$ is rather large, at present it is hard to gain precise data on $BR(ϕ(2170)\to h_1η)$ and $BR(ϕ(2170)\to h_1η')$ whose measurements may be crucial for drawing a definite conclusion about the inner assignment of $ϕ(2170)$. We lay our expectation to the proposed charm-tau factory which will have much larger luminosity and better capacities.

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arXiv2018

How can $X^{\pm}(5568)$ escape detection?

Multi-quark states were predicted by Gell-Mann when the quark model was first formulated. Recently, numerous exotic states that are considered to be multi-quark states have been experimentally confirmed (four-quark mesons and five-quark baryons). Theoretical research indicates that the four-quark state might comprise molecular and/or tetraquark structures. We consider that the meson containing four different flavors $su\bar b\bar d$ should exist and decay via the $X(5568)\to B_sπ$ channel. However, except for the D0 collaboration, all other experimental collaborations have reported negative observations for $X(5568)$ in this golden portal. This contradiction has stimulated the interest of both theorists and experimentalists. To address this discrepancy, we propose that the assumed $X(5568)$ is a mixture of a molecular state and tetraquark, which contributes destructively to $X(5568)\to B_sπ$. The cancellation may be accidental and it should be incomplete. In this scenario, there should be two physical states with the same flavor ingredients, with spectra of $5344\pm307$ and $6318\pm315$. $X(5568)$ lies in the error range of the first state. We predict the width of the second state (designated as $S_2$) as $Γ(X_{S_2}\to B_sπ)=224\pm97$ MeV. We strongly suggest searching for it in future experiments.

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arXiv2018

Estimating decay rate of $X^{\pm}(5568)\to B_sπ^{\pm}$ while assuming them to be molecular states

Discovery of $X(5568)$ brings up a tremendous interest because it is very special, i.e. made of four different flavors. The D0 collaboration claimed that they observed this resonance through portal $X(5568)\to B_sπ$, but unfortunately, later the LHCb, CMS, CDF and ATLAS collaborations' reports indicate that no such state was found. Almost on the Eve of 2017, the D0 collaboration reconfirmed existence of $X(5568)$ via the semileptonic decay of $B_s$. To further reveal the discrepancy, supposing $X(5568)$ as a molecular state, we calculate the decay rate of $X(5568)\rightarrow B_sπ^+$ in an extended light front model. Numerically, the theoretically predicted decay width of $Γ(X(5568)\rightarrow B_sπ^+)$ is $20.28$ MeV which is consistent with the result of the D0 collaboration ($Γ=18.6^{+7.9}_{-6.1}(stat)^{+3.5}_{-3.8}(syst)$ MeV). Since the resonance is narrow, signals might be drowned in a messy background. In analog, two open-charm molecular states $DK$ and $BD$ named as $X_a$ and $X_b$, could be in the same situation. The rates of $X_a\to D_sπ^0$ and $X_b\to B_cπ^0$ are estimated as about 30 MeV and 20 MeV respectively. We suggest the experimental collaborations round the world to search for these two modes and accurate measurements may provide us with valuable information.

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arXiv2018

The semi-leptonic and non-leptonic weak decays of $Λ_b^0$

The recent experimental developments require a more precise theoretical study of weak decays of heavy baryon $Λ_b^0$. In this work, we provide an updated and systematic analysis of both the semi-leptonic and nonleptonic decays of $Λ^0_b$ into baryons $Λ^+_c$, $Λ$, $p$, and $n$. The diquark approximation is adopted so that the methods developed in the $B$ meson system can be extended into the baryon system. The baryon-to-baryon transition form factors are calculated in the framework of a covariant light-front quark model. The form factors $f_3, ~g_3$ can be extracted and are found to be non-negligible. The semi-leptonic processes of $Λ^0_b\to Λ^+_c(p)l^-\barν_l$ are calculated and the results are consistent with the experiment. We study the non-leptonic processes within the QCD factorization approach. The decay amplitudes are calculated at the next-to-leading order in strong coupling constant $α_s$. We calculate the non-leptonic decays of $Λ^0_b$ into a baryon and a s-wave meson (pseudoscalar or vector) including 44 processes in total. The branching ratios and direct CP asymmetries are predicted. The numerical results are compared to the experimental data and those in the other theoretical approaches. Our results show validity of the diquark approximation and application of QCD factorization approach into the heavy baryon system.

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arXiv2017

Determining the effective Wilson coefficient $a_2$ in terms of $BR(B_s\to η_cϕ)$ and evaluating $BR(B_s\to η_cf_0(980))$

In this work, we investigate decays of $B_s\to η_cϕ$ and $B_s\to η_cf_0(980)$ in a theoretical framework. The calculation is based on the postulation that $f_0(980)$ and $f_0(500)$ are mixtures of pure quark states ${1\over\sqrt 2} (\bar uu+\bar dd)$ and $\bar ss$. The hadronic matrix elements for $B_s\to ϕ$ and $B_s\to f_0(980)$ are calculated in the light-front quark model and the important Wilson coefficient $a_2$ which is closely related to non-perturbative QCD is extracted. However, our numerical results indicate that no matter how to adjust the mixing parameter to reconcile contributions of $f_0(980)$ and $f_0(500)$, one cannot make the theoretical prediction on $B_s\to η_c+π^+π^-$ to meet the data. Moreover, the new measurement of $BR(B_s\to J/ψ+f_0(500))<1.7\times 10^{-6}$ also negates the mixture scenario. Thus, we conclude that the recent data suggest that $f_0(980)$ is a four quark state ( tetraquark or $K\bar K$ molecule ), at least the fraction of its pure quark constituents is small.

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arXiv2017

Looking for New Physics via Semi-leptonic and Leptonic rare decays of $D$ and $D_s$

It is well recognized that looking for new physics at lower energy colliders is a tendency which is complementary to high energy machines such as LHC. Based on large database of BESIII, we may have a unique opportunity to do a good job. In this paper we calculate the branching ratios of semi-leptonic processes $D^+_s \to K^+ e^-e^+$, $D^+_s \to K^+ e^-μ^+$ and leptonic processes $D^0 \to e^-e^+$, $D^0 \to e^-μ^+$ in the frames of $U(1)'$ model, 2HDM and unparticle separately. It is found that both the $U(1)'$ and 2HDM may influence the semi-leptonic decay rates, but only the $U(1)'$ offers substantial contributions to the pure leptonic decays and the resultant branching ratio of $D^0 \to e^-μ^+$ can be as large as $10^{-7}\sim10^{-8}$ which might be observed at the future super $τ$-charm factory.

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arXiv2016

The possible $Bπ$ molecular state and its radiative decay

Recently, several exotic bosons have been confirmed as multi-quark states, but there are violent disputes about their inner structures, namely if they are molecular states or tetraquarks, or even mixtures of the two structures. It would be interesting to experimentally search for non-strange four-quark states with open charm or bottom which are lighter than $Λ_c$ or $Λ_b$. Reasonable arguments indicate that they are good candidates of pure molecular states $Dπ$ or $Bπ$ because pions are the lightest boson. Both $Bπ$ and $Dπ$ bound states do not decay via strong interaction. The $Bπ$ molecule may decay into $B^*$ by radiating a photon, whereas $Dπ$ molecule can only decay via weak interaction. In this paper we explore the mass spectra of $Bπ$ molecular statesby solving the corresponding B-S equation. Then the rate of radiative decay $|\frac{3}{2},\frac{1}{2}\rangle\to B^*γ$ is calculated and our numerical results indicate that the processes can be measured by the future experiment. We also briefly discuss the $Dπ$ case, due to the constraint of the final state phase space, it can only decay via weak interaction.

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arXiv2016

Exploring open-charm decay mode $Λ_c\barΛ_c$ of charmonium-like state $Y(4630)$

The newly observed $X, Y, Z$ exotic states are definitely not in the standard $Q\bar Q'$ structures, thus their existence composes a challenge to our understanding on the fundamental principles of hadron physics. Therefore the studies on their decay patterns which are determined by the non-perturbative QCD will definitely shed light on the concerned physics. Generally the four-quark states might be in a molecular state or tetraquark or their mixture. In this work, we adopt the suggestion that $Y(4630)$ is a charmonium-like tetraquark made of a diquark and an anti-diquark. If it is true, its favorable decay mode should be $Y(4630)$ decaying into an open-charm baryon pair, since such a transition occurs via strong interaction and is super-OZI-allowed. In this work, we calculate the decay width of $Y(4630)\toΛ_c\barΛ_c$ in the framework of the quark pair creation (QPC) model. Our numerical results on the partial width computed in the tetraquark configuration coincide with the Belle data within a certain error tolerance.

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arXiv2016

The leptonic CP phase is determined by an equation involving the PMNS matrix elements

Several approximate equalities among the matrix elements of CKM and PMNS imply that hidden symmetries may exist and be common for both quark and neutrino sectors. The CP phase of the CKM matrix ($δ_{\rm CKM}$) is involved in these equalities and can be investigated when these equalities turn into several equations. As we substitute those experimentally measured values of the three mixing angles into the equations for quarks, it is noted that one of the equations which holds exactly has a solution $δ_{\rm CKM}=68.95^\circ$. That value accords with $(69.1^{+2.02}_{-3.85})^\circ$ determined from available data. Generalizing the scenario to the lepton sector, the same equality determines the leptonic CP phase $δ_{\rm PMNS}$ to be $ 276.10^\circ$. Thus we predict the value of $δ_{\rm PMNS}$ from the equation. So far there is no direct measurement on $δ_{\rm PMNS}$ yet, but a recent analysis based on the neutrino oscillation data prefers the phase close to $270^\circ$.

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arXiv2016

Study on decays of $Z_c(4020)$ and $Z_c(3900)$ into $h_c+π$

At the invariant mass spectrum of $h_cπ^\pm$ a new resonance $Z_c(4020)$ has been observed, however the previously confirmed $Z_c(3900)$ does not show up at this channel. In this paper we assume that $Z_c(3900)$ and $Z_c(4020)$ are molecular states of $D\bar D^*(D^{*} \bar D)$ and $D^*\bar D^*$ respectively, then we calculate the transition rates of $Z_c(3900)\to h_c+π$ and $Z_c(4020)\to h_c+π$ in the light front model. Our results show that the partial width of $Z_c(3900)\to h_c+π$ is only three times smaller than that of $Z_c(4020)\to h_c+π$. $Z_c(4020)$ seems to be a molecular state, so if $Z_c(3900)$ is also a molecular state it should be observed in the portal $e^+e^-\to h_cπ^\pm$ as long as the database is sufficiently large, by contrary if the future more precise measurements still cannot find $Z_c(3900)$ at $h_cπ^\pm$ channel, the molecular assignment to $Z_c(3900)$ should be ruled out.

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arXiv2016

The decay of $Λ_b\rightarrow p~K^-$ in QCD factorization approach

With only the tree level operator, the decay of $Λ_b\rightarrow pK$ is predicted to be one order smaller than the experimental data. The QCD penguin effects should be taken into account. In this paper, we explore the one-loop QCD corrections to the decay of $Λ_b\to pK$ within the framework of QCD factorization approach. For the baryon system, the diquark approximation is adopted. The transition hadronic matrix elements between $Λ_b$ and $p$ are calculated in the light front quark model. The branching ratio of $Λ_b\rightarrow pK$ is predicted to be about $4.85\times 10^{-6}$ which is consistent with experimental data $(4.9\pm 0.9)\times 10^{-6}$. The CP violation is about 5\% in theory.

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arXiv2016

Study of structures and dynamical decay mechanisms for multiquark systems

The inner structures of the multiquark states are an interesting subject in hadron physics, generally they may be in tetraquark states which are composed of colored constituents, or in molecular states which are composed of two color singlets, or their mixtures. Therefore, the mechanisms which bind the constituents in a unique system and induce the multiquark states to decay would be different in those cases. In this work, using the quantum mechanics we analyze the dynamical mechanisms inducing decays of the tetraquarks where $Y(4630)$ stands as an example for the study, we also comment on the molecular states without making numerical computations.

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arXiv2016

Study on the rare decays of $Y(4630)$ induced by final state interactions

A resonance $Y(4630)$ at the invariant mass spectrum of $Λ_c \barΛ_c$ observed by the Belle Collaboration triggers a hot discussion about its inner structure. Since it preferably decays into two charmed baryons $Λ_c\barΛ_c$, it is tempted to conjecture it as a tetraquark. Because the dominant decay portal $Y(4630)\to Λ_c \barΛ_c$ is close to the energy threshold, the final state interactions may be significant and result in other baryonic and/or mesonic final states whose branching fractions are sizable to be measured in the future experiments. In this work we calculate the branching ratios of the $Y(4630)$ decays into $p\bar p$, $D^{(*)+} D^{(*)-}$, $π^+π^-$, and $K^+K^-$ which are induced by the $Λ_c \barΛ_c$ re-scattering. The resultant decay patterns will be tested by the future experiments and the consistency degree with the data composes a valuable probe for the tetraquark conjecture.

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arXiv2016

Unified Fano-like interference picture for charmonium-like states $Y(4008)$, $Y(4260)$ and $Y(4360)$

We propose that the unified Fano-like interference picture applies to $e^+e^-\to π^+π^- J/ψ$ and $e^+e^-\to π^+π^- ψ(3686)$, where $Y(4260)$ and $Y(4360)$ are observed, respectively, to provide a reasonable interpretation of the asymmetric lines hapes of $Y(4260)$ and $Y(4360)$ structures. Moreover, the Fano-like interference induces an extra broad structure $Y(4008)$ in $e^+e^-\to π^+π^- J/ψ$ as a companion peak to $Y(4260)$. Three charmonium-like states $Y(4008)$, $Y(4260)$ and $Y(4360)$ observed in $e^+e^-$ annihilation processes are not genuine resonances. Under this scenario, it is well explained why $Y(4008)$, $Y(4260)$ and $Y(4360)$ are absent in the experimental data of the $R$ value scan and missing in open-charm decay channels. Although the present work presents a typical application of the Fano-like interference in particle physics at the lower energy region, we have reason to believe that the Fano-like phenomena may exist in other processes such as $e^+e^-\to π^+π^-ψ(3770)$ and $e^+e^-\to K^+K^- J/ψ$, which will be accessible at BESIII and forthcoming BelleII.

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