Showing papers by "Xiang Liu published in 2010"

X(3915) and X(4350) as new members in the P-wave charmonium family.

Abstract: The analysis of the mass spectrum and the calculation of the strong decay of P-wave charmonium states strongly purport to explain the newly observed X(3915) and X(4350) as new members in the P-wave charmonium family, i.e., chi{c0}{'} for X(3915) and chi{c2}{''} for X(4350). Under the P-wave charmonium assignment to X(3915) and X(4350), the J{PC} quantum numbers of X(3915) and X(4350) must be 0{++} and 2{++} respectively, which provide important criteria to test the P-wave charmonium explanation for X(3915) and X(4350) proposed by this Letter. The decay behavior of the remaining two P-wave charmonium states with the second radial excitation is predicted, and an experimental search for them is suggested.

Newly observed D(2550), D(2610), and D(2760) as 2S and 1D charmed mesons

Abstract: We study three charmed resonances, $D(2550)$, $D(2610)$, and $D(2760)$, newly observed by the BABAR Collaboration, utilizing the mass spectra and investigating the strong decays. Our calculation indicates that $D(2610)$ is an admixture of $2^{3}S_{1}$ and $1^{3}D_{1}$ with ${J}^{P}={1}^{\ensuremath{-}}$. $D(2760)$ can be explained as either the orthogonal partner of $D(2610)$ or $1^{3}D_{3}$. Our estimate of the decay width for $D(2550)$, assuming it as $2^{1}S_{0}$, is far below the experimental value. The decay behavior of the remaining two $1D$ charmed mesons, i.e., $^{3}D_{2}$ and $^{1}D_{2}$ (${J}^{P}={2}^{\ensuremath{-}}$) states, is predicted, which will help future experimental search for these missing $D$-wave charmed mesons.

Observed charmed hadron Λ c (2940) + and the D * N interaction

Abstract: In this work, we systematically study the interaction of D* and nucleon, which is stimulated by the observation of Lambda(c)(2940)(+) close to the threshold of D* p. Our numerical result obtained by the dynamical investigation indicates the existence of the D* N systems with J(P) = 1/2(+/-), 3/2(+/-), which not only provides valuable information to understand the underlying structure of Lambda(c)(2940)(+) but also improves our knowledge of the interaction of D* and nucleon. Additionally, the bottom partners of the D* N systems are predicted, which might be as one of the tasks in LHCb experiment.

Restudy on the wave functions of {Upsilon}(nS) states in the light-front quark model and the radiative decays of {Upsilon}(nS){yields}{eta}{sub b}+{gamma}

Abstract: The light-front quark model has been applied to calculate the transition matrix elements of heavy hadron decays. However, it is noted that using the traditional wave functions of the light-front quark model given in the literature, the theoretically determined decay constants of the {Upsilon}(nS) obviously contradict the data. This implies that the wave functions must be modified. Keeping the orthogonality among the nS states and fitting their decay constants, we obtain a series of the wave functions for {Upsilon}(nS). Based on these wave functions and by analogy with the hydrogen atom, we suggest a modified analytical form for the {Upsilon}(nS) wave functions. Using the modified wave functions, the obtained decay constants are close to the experimental data. Then we calculate the rates of radiative decays of {Upsilon}(nS){yields}{eta}{sub b}+{gamma}. Our predictions are consistent with the experimental data on decays {Upsilon}(3S){yields}{eta}{sub b}+{gamma} within the theoretical and experimental errors.

The molecular systems composed of the charmed mesons in the $H\bar{S}+h.c.$ doublet

Abstract: We study the possible heavy molecular states composed of a pair of charm mesons in the H and S doublets. Since the P-wave charm-strange mesons D s0(2317) and D s1(2460) are extremely narrow, the future experimental observation of the possible heavy molecular states composed of $D_{s}/D_{s}^{\ast}$ and D s0(2317)/D s1(2460) may be feasible if they really exist. Especially the possible J PC =1−− states may be searched for via the initial state radiation technique.

DD̄ production and their interactions

Abstract: $S$- and $P$-wave $D\overline{D}$ scatterings are studied in a meson exchange model with the coupling constants obtained in the heavy quark effective theory. With the extracted $P$-wave phase shifts and the separable potential approximation, we include the $D\overline{D}$ rescattering effect and investigate the production process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}D\overline{D}$. We find that it is difficult to explain the anomalous line shape observed by the BES Collaboration with this mechanism. Combining our model calculation and the experimental measurement, we estimate the upper limit of the nearly universal cutoff parameter to be around 2 GeV. With this number, the upper limits of the binding energies of the $S$-wave $D\overline{D}$ and $B\overline{B}$ bound states are obtained. Assuming that the $S$-wave and $P$-wave interactions rely on the same cutoff, our study provides a way of extracting the information about $S$-wave molecular bound states from the $P$-wave meson pair production.

Long-distant contribution and χ c1 radiative decays to light vector meson

Abstract: The discrepancy between the PQCD calculation and the CLEO data for chi (c1)->gamma V (V=rho (0), omega, phi) stimulates our interest in exploring other mechanisms of chi (c1) decay. In this work, we apply an important non-perturbative QCD effect, i.e., the hadronic loop mechanism, to study chi (c1)->gamma V radiative decay. Our numerical result shows that the theoretical results including the hadronic loop contribution and the PQCD calculation of chi (c1)->gamma V are consistent with the corresponding CLEO data of chi (c1)->gamma V. We expect further experimental measurement of chi (c1)->gamma V, which will be helpful to test the hadronic loop effect on chi (c1) decay.

Long-distant contribution and $\chi_{c1}$ radiative decays to light vector meson

Abstract: The discrepancy between the PQCD calculation and the CLEO data for $\chi_{c1}\to \gamma V$ ($V=\rho^0,\,\omega,\,\phi$) stimulates our interest in exploring extra mechanism of $\chi_{c1}$ decay. In this work, we apply an important non-perturbative QCD effect, i.e., hadronic loop mechanism, to study $\chi_{c1}\to \gamma V$ radiative decay. Our numerical result shows that the theoretical results including the hadronic loop contribution and the PQCD calculation of $\chi_{c1}\to \gamma V$ are consistent with the corresponding CLEO data of $\chi_{c1}\to \gamma V$. We expect further experimental measurement of $\chi_{c1}\to \gamma V$ at BES-III, which will be helpful to test the hadronic loop effect on $\chi_{c1}$ decay.

Understanding the branching ratios of $\chi_{c1}\to\phi\phi$, $\omega\omega$, $\omega\phi$ observed at BES-III

Abstract: In this work, we discuss the contribution of the mesonic loops to the decay rates of chi(c1) -> phi phi, omega omega, which are suppressed by the helicity selection rules and chi(c1) -> phi omega, which is a double- Okubo- ZweigIizuka forbidden process. We find that the mesonic loop effects naturally explain the clear signals of chi(c1) -> phi phi, omega omega decay modes observed by the BES Collaboration. Moreover, we investigate the effects of the omega - phi mixing, which may result in the order of magnitude of the branching ratio BR(chi(c1) -> omega phi) being 10(-7). Thus, we are waiting for the accurate measurements of the BR(chi(c1) -> omega omega), BR(chi(c1) -> phi phi) and BR(chi(c1) -> omega phi) which may be very helpful for testing the long- distant contribution and the omega - phi mixing in chi(c1) -> phi phi, omega omega, omega phi decays.

B-(*())(B)over-bar(()*()) intermediate states contribution to Gamma(4S, 5S) -> eta(b) + gamma radiative decay

Abstract: In this work, we investigate the rescattering effects in the radiative decay Gamma(5S) -> eta(b) + gamma , which were suggested to be crucially important for understanding the anomalous largeness of the branching ratios B(Gamma(5S) -> Gamma(1S) + pi pi) and B(Gamma(5S) -> Gamma(1S) + eta). Our calculations show that the rescattering effects may enhance Gamma(Gamma(10860) -> eta(b) +gamma) by four orders, but the tetraquark structure does not. Recently the BABAR and CLEO collaborations have measured the mass of eta(b) and the branching ratios B(Gamma(2S) -> eta(b) +gamma), B(Gamma(3S) -> eta(b) +gamma). We hope that very soon, Gamma(10860) -> eta(b) + gamma) will be measured and it would be an ideal opportunity for testing whether the rescattering or the tetraquark structure is responsible for the anomaly of B(Gamma(5S) -> Gamma(nS) pi(+) pi(-))(n = 1, 2, 3)), i. e., the future measurements on the radiative decays of Gamma(5S) might be a touchstone of the two mechanisms.

Study on the radiative decays of $\Upsilon(nS)\to \eta_b+\gamma$

Abstract: In this work, we investigate the characteristics of the spin-singlet state $\eta_b$ of the bottomonia family via the radiative decays of $\Upsilon(nS)\to \eta_b+\gamma$. The theoretical estimation of the decay widths is carried out in terms of the light-front quark model (LFQM). Recently CLEO and BaBar collaborations have measured $\mathcal{B}(\Upsilon(3S)\to\gamma\eta_b)$ and the mass of ${\eta_b}$. In terms of the data we fix the concerned input parameters in our calculations of $\Upsilon(nS)\to \eta_b+\gamma$. A special attention is paid on the transition of $\Upsilon(5S)\to \eta_b+\gamma$. The BELLE data showed that the width of $\Upsilon(5S)\to \Upsilon(2S,1S)+\pi\pi$ is two orders larger than that of $\Upsilon(4S)\to \Upsilon(2S,1S)+\pi\pi$, thus some theoretical explanations have been proposed. Among them, it is suggested the inelastic final state interaction (IFSI) $\Upsilon(5S)\to B\bar B\to \Upsilon(1S)+\pi\pi$ may be a natural one. If so, a similar mechanism also applies to $\Upsilon(5S)\to B^{(*)}\bar B^{(*)}\to \eta_b+\gamma$, the precise measurement would serve as a good test whether $\Upsilon(5S)$ possess exotic components. Our calculation in the LFQM indicates that the rate of the direct process $\Upsilon(5S)\to\eta_b+\gamma$ is not anomalous compared to $\Upsilon(mS)\to\eta_b+\gamma (m=1,2,3,4)$, thus if the IFSI does apply, the rate of $\Upsilon(5S)\to\eta_b+\gamma$ should be larger than the others by orders.

The molecular systems composed of the charmed mesons in the $H\bar{S}+h.c.$ doublet

Abstract: We study the possible heavy molecular states composed of a pair of charm mesons in the H and S doublets. Since the P-wave charm-strange mesons $D_{s0}(2317)$ and $D_{s1}(2460)$ are extremely narrow, the future experimental observation of the possible heavy molecular states composed of $D_s/D_s^\ast$ and $D_{s0}(2317)/D_{s1}(2460)$ may be feasible if they really exist. Especially the possible $J^{PC}=1^{--}$ states may be searched for via the initial state radiation technique.

Possible heavy molecular states composed of a pair of excited charm-strange mesons

Abstract: The P-wave charm-strange mesons $D_{s0}(2317)$ and $D_{s1}(2460)$ lie below the $DK$ and $D^\ast K$ threshold respectively. They are extremely narrow because their strong decays violate the isospin symmetry. We study the possible heavy molecular states composed of a pair of excited charm strange mesons. As a byproduct, we also present the numerical results for the bottonium-like analogue.