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Yan-Rui Liu
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ABSTRACT: In the heavy quark limit, we discuss the spin of the charm-anticharm pair
$J_{c\bar{c}}$ in an S-wave meson-antimeson molecule or resonance. One finds
two cases that $J_{c\bar{c}}$ cannot be 0: (a) $J=|j_2-j_4|-1$ or $J=j_2+j_4+1$
where $J$ is the total spin of the system and $j_2$ ($j_4$) is the total
angular momentum of the light degree of freedom in a charmed meson (antimeson);
(b) $J^C=1^+,2^-,3^+,...$, if the two different mesons belong to the same
doublet. The decays to spin-singlet charmonium states are suppressed when one
of the two conditions is satisfied. We discuss constrained decay properties for
selected systems.
04/2013;
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ABSTRACT: Motivated by the observation of several molecule candidates in the heavy
quark sector, we discuss the possibility of a state with $J^{PC}=3^{-+}$. In a
one-boson-exchange model investigation for the S wave $C=+$ $D^*\bar{D}_2^*$
states, one finds that the strongest attraction is in the case J=3 and I=0 for
both $\pi$ and $\sigma$ exchanges. Numerical analysis indicates that this
hadronic bound state may exist. If a state around the $D^*\bar{D}_2^*$
threshold ($\approx$4472 MeV) in the channel $J/\psi\omega$ (P wave) is
observed, the heavy quark spin symmetry implies that it is not a $c\bar{c}$
meson and the $J^{PC}$ are very likely to be $3^{-+}$.
02/2013;
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ABSTRACT: Structure and production of doubly charmed tetraquarks T_cc (cc ubar dbar)
are studied from the viewpoint of color configurations. Based on the diquark
correlation, the tetraquark T_cc with I(JP)=0(1+) is considered to be stable
against strong decay. We discuss that the mixing probability of color
antitriplet and sextet cc components in T_cc is suppressed by 1/m_c^2, so the
two configurations are separately realized in the heavy quark limit. Utilizing
the nonrelativistic QCD framework, we evaluate the production cross sections of
T_cc in electron-positron collisions. The momentum dependence of the cross
section of color antitriplet is found to be different from that of sextet,
which can be used to discriminate the color structure of the T_cc states in
experimental measurements.
09/2012;
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ABSTRACT: S and P wave D scatterings are studied in a meson exchange model. When exploring their production in the e+e− annihilation process, we have considered the rescattering effect in a nonrelativistic method. We find that this effect may result in an anomalous line shape of the cross section provided that the final state interaction is unrealistically strong. However, it is difficult to understand the anomalous line shape observed by the BES collaboration with this mechanism. From the normal line shape for the B case, we set a constraint for the model parameters and further get an upper limit for the S wave binding solutions.
Journal of Physics Conference Series 09/2011; 312(3):032012.
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ABSTRACT: Possible $\Lambda_c\Lambda_c$ hadronic molecule is investigated in the
one-pion-exchange potential model. In the study with this model, the heavier
meson exchange effects are encoded into a phenomenological cutoff parameter and
couplings to the nearby $\Sigma_c\Sigma_c$, $\Sigma_c\Sigma_c^*$, and
$\Sigma_c^*\Sigma_c^*$ channels are essential. From the numerical results, we
find that a molecular bound state of two $\Lambda_c$'s is possible, where the
tensor force plays a crucial role, although the binding energies are sensitive
to the cutoff parameter.
05/2011;
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ABSTRACT: We have systematically studied the S-wave pseudoscalar meson and heavy vector meson scattering lengths to the third order with the chiral perturbation theory, which will be helpful to reveal their strong interaction. For comparison, we have presented the numerical results of the scattering lengths (1) in the framework of the heavy meson chiral perturbation theory and (2) in the framework of the infrared regularization. The chiral expansion converges well in some channels.
Phys. Rev. D. 04/2011; 84(3).
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ABSTRACT: The one-boson exchange potential model for $\Lambda_cN$ is constructed and
the possibility of $\Lambda_cN$ bound states is examined. We consider an
effective Lagrangian for the charmed baryons, $\Lambda_c$, $\Sigma_c$, and
$\Sigma_c^*$, reflecting the heavy quark symmetry, chiral symmetry, and hidden
local symmetry. We determine the coupling constants using various methods. With
the derived nonrelativistic potentials, we study the bound state problem of the
$\Lambda_cN$ system and relevant coupled channel effects. It is found that
molecular bound states of $\Lambda_cN$ are plausible, for which the channel
couplings of $\Sigma_cN$ and $\Sigma_c^*N$ are essential.
03/2011;
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ABSTRACT: We have systematically calculated the S-wave pseudoscalar meson and decuplet
baryon scattering lengths to the third order in the small scale expansion
scheme of the heavy baryon chiral perturbation theory. We hope the future study
may test the framework and the present predictions.
11/2010;
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ABSTRACT: S- and P-wave DD̅ 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 DD̅ rescattering effect and investigate the production process e+e-→DD̅ . 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 DD̅ and BB̅ 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.
Phys. Rev. D. 07/2010; 82(1).
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ABSTRACT: S and P wave $D\bar{D}$ 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 $D\bar{D}$ rescattering effect and investigate the production process $e^+e^-\to D\bar{D}$. 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 1.7 GeV. With this number, the upper limits of the binding energies of the S wave $D\bar{D}$ and $B\bar{B}$ 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. Comment: 22 pages, 14 figures, 5 tables, publication version
05/2010;
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ABSTRACT: We investigated the bound state problem of the S wave charged $D_1 \bar{D}^*$ ($D_1' \bar{D}^*$) system in a chiral quark model by solving the resonating group method equation. Our preliminary study does not favor the molecular assumption of $Z^+(4430)$. On the contrary, if $Z^+(4430)$ is really a molecule, its partner with opposite $G$-parity should also exist and probably may be found in the $\pi^+\eta_c(2S)$, $J/\psi \pi^+\pi^0$, or $\psi'\pi^+\pi^0$ channel. For the bottom systems, we found the existence of both $I^G$=$1^+$ and $I^G$=$1^-$ $B_1 \bar{B}^*$ ($B_1' \bar{B}^*$) molecules is possible. Comment: 6 pages, 3 figures
08/2009;
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ABSTRACT: We have performed a systematical calculation of the pion ($\pi, K, \eta$) and heavy pseudoscalar meson S-wave scattering lengths up to ${\cal O}(p^3)$ in the chiral perturbation theory in the heavy quark symmetry limit. With the three scattering lengths from the lattice simulations as input we estimate the unknown low-energy constants. Then we predict all the other unmeasured scattering lengths. The analytical expressions and predictions may be helpful to future investigations. Especially we note that the DK scattering length is positive. Therefore their interaction is attractive, which helps to lower the mass of the "bare" charm-strange scalar state in the quark model through the couple-channel effect. Comment: 7 pages, 1 figure, 3 tables, accepted by Phys. Rev. D
04/2009;
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ABSTRACT: The bound state problem of D0 Dmacr *0( Dmacr
0D*0) is relevant to the molecular interpretation
of the X(3872). We investigated this problem in a chiral quark model by
solving the resonating group method equation. We found the system is
unbound through S-wave π and σ interactions. The inclusion of
ρ and ω meson exchanges is helpful to the formation of a
molecule. Because the binding energy relies on the coupling constants,
we cannot draw a definite conclusion as to whether a molecular state
exists in the D0 Dmacr *0( Dmacr
0D*0) system. When moving on to the bottom
counterpart, we obtained an S-wave B Bmacr * state.
Physical Review C 02/2009; 79(3):35206. · 3.31 Impact Factor
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ABSTRACT: We investigated systematically whether the S-wave ($\bar{Q}q$) meson and the ($Q\bar{q}$) meson may form S-wave bound states in a chiral SU(3) quark model by solving the resonating group method equation. Here $Q=c$ or $b$ and $q=u$, $d$ or $s$. Our preliminary calculation disfavors the existence of $I=\frac12$ ($\bar{Q}l$)-($Q\bar{s}$) molecules ($l=u,d$) while favors the existence of isoscalar $B\bar{B}$, $B^*\bar{B}^*$ (J=2) and $B\bar{B}^*$ (C=+) molecules. The existence of isovector (charm-anticharm) and (charm-bottom) molecules is also disfavored. Therefore the resonance-like structure $Z^+(4051)$ is unlikely to be an S-wave $D^*\bar{D}^*$ molecule. Comment: 8 pages, 7 tables, accepted by Phys. Rev. C
10/2008;
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ABSTRACT: We perform a systematic study of the possible molecular states composed of a pair of heavy mesons such as $D\bar D$, $D^\ast\bar D$, $D^\ast \bar D^\ast$ in the framework of the meson exchange model. The exchanged mesons include the pseudoscalar, scalar and vector mesons. Through our investigation, we find that (1) the structure X(3764) is not a molecular state; (2) There exists strong attraction in the range $r < 1$ fm for the $D^*\bar D^*$ system with $J=0, 1$. If future experiments confirm $Z^+(4051)$ as a loosely bound molecular state, its quantum number is probably $J^{P}=0^+$. Its partner state $\Phi^{**0}$ may be searched for in the $\pi^0\chi_{c1}$ channel; (3) The vector meson exchange provides strong attraction in the $D^\ast \bar D$ channel together with the pion exchange. A bound state solution exists with a reasonable cutoff parameter $\Lambda\sim 1.4$ GeV. X(3872) may be accommodated as a molecular state dynamically although drawing a very definite conclusion needs further investigation; (4) The $B^\ast \bar B$ molecular state exists. Comment: 21 pages, 17 tables, 11 figures. Typos corrected
08/2008;
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ABSTRACT: The bound state problem of $D^0\bar{D}^{\ast0}$ ($\bar{D}^0{D}^{\ast0}$) is relevant to the molecular interpretation of the X(3872). We investigated this problem in a chiral quark model by solving the resonating group method equation. We found the system is unbound through S-wave $\pi$ and $\sigma$ interactions. The inclusion of $\rho$ and $\omega$ meson exchanges is helpful to the formation of a molecule. Because the binding energy relies on the coupling constants, we cannot draw a definite conclusion whether a molecular state exists in $D^0\bar{D}^{\ast0}$ ($\bar{D}^0{D}^{\ast0}$) system. When moving on to the bottom counterpart, we obtained an S-wave $B\bar{B}^\ast$ state. Comment: 8 pages, 2 figures, 7 tables, published in Phys. Rev. C
05/2008;
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ABSTRACT: We reexamine whether $Z^+(4430)$ could be a $D_1'-{D}^*$ or $D_1-{D}^*$ molecular state after considering both the pion and $\sigma$ meson exchange potentials and introducing the form factor to take into account the structure effect of the interaction vertex. Our numerical analysis with Matlab package MATSLISE indicates the contribution from the sigma meson exchange is small for the $D_1'-{D}^*$ system and significant for the $D_1-{D}^*$ system. The S-wave $D_1-\bar{D}^*$ molecular state with only $J^{P}=0^-$ and $D_1'-{D}^*$ molecular states with $J^P=0^-,1^-,2^-$ may exist with reasonable parameters. One should investigate whether the broad width of $D_1'$ disfavors the possible formation of molecular states in the future. The bottom analog $Z_B$ of $Z^+(4430)$ has a larger binding energy, which may be searched at Tevatron and LHC. Experimental measurement of the quantum number of $Z^+(4430)$ may help uncover its underlying structure.
04/2008;
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ABSTRACT: After taking into account both the pion and sigma meson exchange potential, we have performed a dynamical calculation of the $D^0\bar{D}^{\ast0}$ system. The $\sigma$ meson exchange potential is repulsive from heavy quark symmetry and numerically important for a loosely bound system. Our analysis disfavors the interpretation of X(3872) as a loosely bound molecular state if we use the experimental $D^\ast D\pi$ coupling constant $g=0.59$ and a reasonable cutoff around 1 GeV, which is the typical hadronic scale. Bound state solutions with negative eigenvalues for the $D\bar{D}^\ast$ system exist only with either a very large coupling constant (two times of the experimental value) or a large cutoff ($\Lambda \sim 6$ GeV or $\beta \sim 6$ GeV$^2$). In contrast, there probably exists a loosely bound S-wave $B\bar{B}^\ast$ molecular state. Once produced, such a molecular state would be rather stable since its dominant decay mode is the radiative decay through $B^\ast\to B \gamma$. Experimental search of these states will be very interesting.
02/2008;
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ABSTRACT: In this talk, we review our recent work about the dynamical studies of $Z^+(4430)$ and X(3872). $Z^+(4430)$ can not be explained as a $D_1'D^*$ or $D_1D^*$ molecular state only considering one pion exchange potential without the cutoff, which needs to be confirmed by introducing sigma exchange potential and adding the cutoff in the effective potential. One also excludes the possibility of X(3872) as a $DD^*$ molecular state by one pion and one sigma exchanges with the cutoff. Fortunately there exists an S-wave $BB^*$ bound state with $J^{PC}=1^{++}$. we suggest future experiment to search this state. Comment: 6 pages, contribution to the Workshop on "Scalar meson and Related topics" (Scadron 70), during Feb 11-16, 2008, at IST, Lisbon, Portugal
02/2008;
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ABSTRACT: Since $Z^+(4430)$ lies very close to the threshold of $D^\ast{\bar D}_1$, we investigate whether $Z^+(4430)$ could be a loosely bound S-wave state of $D^\ast{\bar D}_1$ or $D^\ast{\bar D}^\prime_1$ with $J^P=0^-, 1^-, 2^-$, i.e., a molecular state arising from the one-pion-exchange potential. The potential from the crossed diagram is much larger than that from the diagonal scattering diagram. With various trial wave functions, we notice that the attraction from the one pion exchange potential alone is not strong enough to form a bound state with realistic pionic coupling constants deduced from the decay widths of $D_1$ and $D^\prime_1$.
12/2007;
