arXiv subjects

Ce Meng

Publications and source records attributed to Ce Meng.

32 records · Page 2Linked to original sources

arXiv2012

B-meson Semi-inclusive Decay to $2^{-+}$ Charmonium in NRQCD and X(3872)

The semi-inclusive B-meson decay into spin-singlet D-wave $2^{-+}$ charmonium, $B\to η_{c2}+X$, is studied in nonrelativistic QCD (NRQCD). Both color-singlet and color-octet contributions are calculated at next-to-leading order (NLO) in the strong coupling constant $α_s$. The non-perturbative long-distance matrix elements are evaluated using operator evolution equations. It is found that the color-singlet $^1D_2$ contribution is tiny, while the color-octet channels make dominant contributions. The estimated branching ratio $B(B\to η_{c2}+X)$ is about $0.41\,\times10^{-4}$ in the Naive Dimensional Regularization (NDR) scheme and $1.24\,\times10^{-4}$ in the t'Hooft-Veltman (HV) scheme, with renormalization scale $μ=m_b=4.8$\,GeV. The scheme-sensitivity of these numerical results is due to cancelation between ${}^1S_0^{[8]}$ and ${}^1P_1^{[8]}$ contributions. The $μ$-dependence curves of NLO branching ratios in both schemes are also shown, with $μ$ varying from $\frac{m_b}{2}$ to $2m_b$ and the NRQCD factorization or renormalization scale $μ_Λ$ taken to be $2m_c$. Comparison of the estimated branching ratio of $B\to η_{c2}+X$ with the observed branching ratio of $B \to X(3872)+K$ may lead to the conclusion that X(3872) is unlikely to be the $2^{-+}$ charmonium state $η_{c2}$.

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arXiv2012

Search for $χ_{c_J}(2P)$ from Higher Charmonim E1 Transitions and X,Y,Z States

We calculate the E1 transition widths of higher vector charmonium states into the spin-triplet 2P states in three typical potential models, and discuss the possibility to detect these 2P states via these E1 transitions. We attempt to clarify the nature of some recently observed X,Y,Z states by comparing them with these 2P charmonium states in these E1 transitions. In particular, the calculated branching ratios of $ψ(4040),ψ(4160)\to χ^{'}_{c_J}γ$ (J=0,1,2) are found to be in the range of $10^{-4}-10^{-3}$, and sensitive to the 3S-2D mixing of $ψ(4040)$ and $ψ(4160)$. The mixing angle may be constrained by measuring $ψ(4040),ψ(4160)\to Z(3930)γ$, if Z(3930) is identified with the $χ^{'}_{c_2}$ state, and then be used in measuring $χ^{'}_{c_{0,1}}$ states. These processes can be studied experimentally at $e^+e^-$ colliders such as BEPCII/BESIII and CESR/CLEO.

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arXiv2009

Coupled-Channel and Screening Effects in Charmonium Spectrum

Using the same quenched limit as input, we compare the charmonium spectra predicted by the coupled-channel model and the screened potential model in the mass region below 4 GeV, in which the contributions from decay channels involving P-wave (as well as even higher excited) D mesons can be neglected. We find that the two models have similar global features in describing charmonium spectrum since they embody the same effect of the vacuum polarization of dynamical light quark pairs. This agreement is encouraging for using the screened potential to further describe the mass spectrum of higher charmonium in the region above 4 GeV. Applying both models will be helpful to clarify the nature of the newly discovered "X,Y,Z" mesons in B-factories and other experiments. In particular, we show the S-wave decay coupling effect on lowering the $χ_{c1}(2P)$ mass towards the $D\bar {D^*}$ threshold, in support of the assignment of the X(3872) as a $χ_{c1}(2P)$-dominated charmonium state.

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arXiv2008

$Υ(4S,5S)\toΥ(1S)η$ transitions in the rescattering model and the new BaBar measurement

The $η$ transitions of $Υ(4S,5S)$ into $Υ(1S,2S)$ are studied in the rescattering model by considering the final state interactions above the $B\bar B$ threshold. The width of the $η$ transition of $Υ(4S)$ into $Υ(1S)$ is found to be larger than that of the dipion transition, and the ratio of $Γ(Υ(4S)\toΥ(1S)η)$ to $Γ(Υ(4S)\toΥ(1S)π^+π^-)$ is predicted to be $R_4=1.8{-}4.5$, which is about two orders of magnitude larger than the expectation of the conventional hadronic transition theory, and is supported by the new BaBar measurement. The widths of the $η$ transitions of $Υ(5S)$ are found to be sensitive to the coupling constants $g_{Υ(5S)B^{(*)}B^{(*)}}$ due to a large cancelation between contributions from the $B\bar{B}$, $B^*\bar{B}+c.c.$, and $B^*\bar{B}^*$ channels, and only a rough estimate $Γ(Υ(5S)\toΥ(1S,2S)η)=10{-}200$ KeV can be given. The widths of the $η'$ transitions of $Υ(4S,5S)$ are also discussed, and they could be much smaller than that of the corresponding $η$ transitions mainly due to the tiny phase space.

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arXiv2008

Peak shifts due to $B^{()}-\bar{B}^{()}$ rescattering in $Υ(5S)$ dipion transitions

We study the energy distributions of dipion transitions $Υ(5S)$ to $Υ(1S,2S,3S)π^+π^-$ in the final state rescattering model. Since the $Υ(5S)$ is well above the open bottom thresholds, the dipion transitions are expected to mainly proceed through the real processes $Υ(5S)\to B^{(*)}\bar{B}^{(*)}$ and $B^{(*)}\bar{B}^{(*)}\to Υ(1S,2S,3S)π^+π^-$. We find that the energy distributions of $Υ(1S,2S,3S)π^+π^-$ markedly differ from that of $Υ(5S)\to B^{(*)}\bar{B}^{(*)}$. In particular, the resonance peak will be pushed up by about 7-20 MeV for these dipion transitions relative to the main hadronic decay modes. These predictions can be used to test the final state rescattering mechanism in hadronic transitions for heavy quarkonia above the open flavor thresholds.

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arXiv2008

Scalar Resonance Contributions to the Dipion Transition Rates of $Υ(4S,5S)$ in the re-scattering model

In order to explain the observed unusually large dipion transition rates of $Υ(10870)$, the scalar resonance contributions in the re-scattering model to the dipion transitions of $Υ(4S)$ and $Υ(5S)$ are studied. Since the imaginary part of the re-scattering amplitude is expected to be dominant, the large ratios of the transition rates of $Υ(10870)$, which is identified with $Υ(5S)$, to that of $Υ(4S)$ can be understood as mainly coming from the difference between the $p$-values in their decays into open bottom channels, and the ratios are estimated numerically to be about 200-600 with reasonable choices of parameters. The absolute and relative rates of $Υ(5S)\toΥ(1S,2S,3S)π^+π^-$ and $Υ(5S)\toΥ(1S)K^+K^-$ are roughly consistent with data. We emphasize that the dipion transitions observed for some of the newly discovered $Y$ states associated with charmonia may have similar features to the dipion transitions of $Υ(5S)$. Measurements on the dipion transitions of $Υ(6S)$ could provide further test for this mechanism.

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arXiv2007

$Z^+(4430)$ as a resonance in the $D_1(D_1^\prime)D^*$ channel

We study the possibility that the $Z^+(4430)$ state observed by Belle is a $D_1D^*$ (or $D_1'D^*$) resonance in S-wave. Focusing on its decays, We find that the open-charm decay into $D^*D^*π$ is dominant. Furthermore, we use the re-scattering mechanism to study its hidden-charm decays and find that the re-scattering effects are significant in $D_1D^*$ channel but not in $D_1'D^*$ channel. For the $J^P=1^-$ candidate, with chosen parameters, we can get $Γ(Z^+\toψ'π^+)/Γ(Z^+\to J/ψπ^+)\thickapprox 5.3$, which tends to account for why the $Z^+(4430)$ is difficult to be found in $J/ψπ^+$. However, the $0^-$ candidate can not be ruled out by our calculations.

hep-ph↗

arXiv2007

Decays of the X(3872) and $χ_{c1}(2P)$ charmonium

We re-examine the re-scattering mechanism for the X(3872), as a candidate for the 2P charmonium state $χ_{c1}(2P)$, decaying to $J/ψρ(ω)$ through exchanging $D^{(*)}$ mesons between intermediate states $D(\bar{D})$ and $\bar{D}^*(D^*)$. We evaluate the dispersive part, as well as the absorptive one, of the re-scattering amplitude and find that the contribution from the dispersive part is dominant even when X(3872) lies above the threshold of the neutral channel $th_n=m_{D^0}+m_{D^{*0}}$. We predict $R_{ρ/ω}\simeq 1$ for the $m_X$ region scanned by experiments. Meanwhile, we also estimate the rate of $X\to D^0\bar{D}^{0}π^0$. Our results favor a charmonium interpretation of X(3872) when it lies slightly below the threshold of $D^0\bar{D}^{*0}$. Furthermore, we evaluated the width of $X\to J/ψρ$ with the help of a phenomenological effective coupling constant $g_X$, and find the total width of X(3872) to be in the range of 1-2 MeV.

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arXiv2006

Puzzles in $B\to h_c(χ_{c2})K$ Decays and QCD Factorization

We study the factorization-forbidden decays $B\to h_c K$ and $B\toχ_{c2}K$ in the QCD factorization approach. If neglecting the vertex corrections and regularizing the end-point singularities in spectator corrections properly, we get small branching ratios for both the two decay modes, which are roughly consistent with the experimental upper limits. This is in contrast to another factorization-forbidden decay $B\to χ_{c0}K$, for which a large decay rate is obtained in the same approach.

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arXiv2006

Nonfactorizable $B\toχ_{c0}K$ decay and QCD factorization

We study the unexpectedly large rate for the factorization-forbidden decay $B\to χ_{c0}K$ within the QCD factorization approach. We use a non-zero gluon mass to regularize the infrared divergences in vertex corrections. The end-point singularities arising from spectator corrections are regularized and carefully estimated by the off-shellness of quarks. We find that the contributions arising from the vertex and leading-twist spectator corrections are numerically small, and the twist-3 spectator contribution with chiral enhancement and linear end-point singularity becomes dominant. With reasonable choices for the parameters, the branching ratio for $B\toχ_{c0}K$ decay is estimated to be in the range $(2-4)\times 10^{-4}$, which is compatible with the Belle and BaBar data.

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arXiv2006

$ψ(3770)$ and $B$ meson exclusive decay $B \to ψ(3770) K$ in QCD factorization

Belle has observed surprisingly copious production of $ψ(3770)$ in $B$ meson decay $B\to ψ(3770)K$, of which the rate is comparable to that of $B\to ψ(3686)K$. We study this puzzling process in the QCD factorization approach with the effect of S-D mixing considered. We find that the soft scattering effects in the spectator interactions play an essential role. With a proper parametrization for the higher twist soft end-point singularities associated with kaon, and with the S-D mixing angle $θ=-12^{\circ}$, the calculated decay rates can be close to the data. Implications of these soft spectator effects to other charmonium production in $B$ exclusive decays are also emphasized.

hep-ph↗

arXiv2005

$B\toχ_{c1}(1P,2P)K$ decays in QCD factorization and X(3872)

$B\toχ_{c1}(1P,2P)K$ decays are studied in QCD factorization by treating charmonia as nonrelativistic bound states. No infrared divergences exist in the vertex corrections, while the logarithmic end-point singularities in the hard spectator corrections can be regularized by a momentum cutoff. With certain uncertainties we find that the $B\toχ_{c1}(2P)K$ decay rate can be comparable to $B\toχ_{c1}(1P)K$, and get $Br(B^0 \to χ_{c1}' K^0) =Br(B^+ \to χ_{c1}' K^+)\approx 2\times 10^{-4}$. This might imply a possible interpretation for the newly discovered X(3872) that this state has a dominant $J^{PC} = 1^{++}(2P)$ $c\bar c$ component but mixed with a substantial $D^0\bar{D}^{*0}+D^{*0}\bar{D}^0$ continuum component.

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arXiv2003

Infrared divergences of $B$ meson exclusive decays to P-wave charmonia in QCD factorization and nonrelativistic QCD

In the framework of QCD factorization, we study the $B$ meson exclusive decays $B\to χ_{cJ}K$ where the spin-triplet P-wave charmonium states $χ_{cJ}(J=0,1,2)$ are described by the color-singlet non-relativistic wave functions. We find that for these decays (except $χ_{c1}$) there are infrared divergences arising from nonfactorizable vertex corrections as well as logarithmic end-point singularities arising from nonfactorizable spectator interactions at leading-twist order. The infrared divergences due to vertex corrections will explicitly break down QCD factorization within the color-singlet model for charmonia. Unlike in the inclusive decays where the higher Fock states with color-octet $c \bar c$ pair and soft gluon can make contributions to remove the infrared divergences, their contributions can not be accommodated in the exclusive two body decays. As a result, the infrared divergences encountered in exclusive processes involving charmonia may raise a new question to the QCD factorization and NRQCD factorization in B exclusive decays.

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arXiv2002

B ->η_c K(η_c^\prime K) decays in QCD factorization

We study the exclusive decays of $B$ meson into pseudoscalar charmonium states $η_c$ and $η_c^\prime$ within the QCD factorization approach and find that the nonfactorizable corrections to naive factorization are infrared safe at leading-twist order. The spectator interactions arising from the kaon twist-3 effects are formally power-suppressed but chirally and logarithmically enhanced. The theoretical decay rates are too small to accommodate the experimental data. On the other hand, we compare the theoretical calculations for $J/ψ, ψ^\prime$, and $η_c, η_c^\prime$, and find that the predicted relative decay rates of these four states are approximately compatible with experimental data.

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