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Register a new userCan X(3915) be the tensor partner of the X(3872)?
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It has been proposed recently (Phys. Rev. Lett. 115 (2015), 022001) that the charmoniumlike state named X(3915) and suggested to be a $0^{++}$ scalar, is just the helicity-0 realisation of the $2^{++}$ tensor state $chi_{c2}(3930)$. This scenario would call for a helicity-0 dominance, which were at odds with the properties of a conventional tensor charmonium, but might be compatible with some exotic structure of the $chi_{c2}(3930)$. In this paper, we investigate, if such a scenario is compatible with the assumption that the $chi_{c2}(3930)$ is a $D^*bar D^*$ molecular state - a spin partner of the $X(3872)$ treated as a shallow bound state. We demonstrate that for a tensor molecule the helicity-0 component vanishes for vanishing binding energy and accordingly for a shallow bound state a helicity-2 dominance would be natural. However, for the $chi_{c2}(3930)$, residing about 100 MeV below the $D^*bar D^*$ threshold, there is no a priori reason for a helicity-2 dominance and thus the proposal formulated in the above mentioned reference might indeed point at a molecular structure of the tensor state. Nevertheless, we find that the experimental data currently available favour a dominant contribution of the helicity-2 amplitude also in this scenario, if spin symmetry arguments are employed to relate properties of the molecular state to those of the X(3872). We also discuss what research is necessary to further constrain the analysis.
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We introduce a near-threshold parameterization that is more general than the effective-range expansion up to and including the effective-range because it can also handle with a near-threshold zero in the $D^0bar{D}^{*0}$ $S$-wave. In terms of it we analyze the CDF data on inclusive $pbar{p}$ scattering to $J/psi pi^+pi^-$, and the Belle and BaBar data on $B$ decays to $K, J/psi pi^+pi^-$ and $K Dbar{D}^{*0}$ around the $D^0bar{D}^{*0}$ threshold. It is shown that data can be reproduced with similar quality for the $X(3872)$ being a bound {it and/or} a virtual state. We also find that the $X(3872)$ might be a higher-order virtual-state pole (double or triplet pole), in the limit in which the small $D^{*0}$ width vanishes. Once the latter is restored the corrections to the pole position are non-analytic and much bigger than the $D^{*0}$ width itself. The $X(3872)$ compositeness coefficient in $D^0bar{D}^{*0}$ ranges from nearly 0 up to 1 in the different scenarios.
The $D^{(ast)}Xi_{cc}^{(ast)}$ system and $bar{Xi}_{cc}^{(ast)}Xi_{cc}^{(ast)}$ system can be related to the $D^{(ast)}bar{D}^{(ast)}$ system via heavy anti-quark di-quark symmetry (HADS). In this work, we employ a contact-range effective field theory to systematically investigate the likely existence of molecules in these systems in terms of the hypothesis that X(3872) is a $1^{++}$~$Dbar{D}^{ast}$ bound state in the isospin symmetry limit, with some of the unknown low energy constants estimated using the light-meson saturation approximation. In the meson-meson system, a $J^{PC}=2^{++}$~$bar{D}^{ast}D^{ast}$ molecule commonly referred to as $X(4013)$ is reproduced, which is the heavy quark spin partner of $X(3872)$. In the meson-baryon system, we predict two triply charmed pentaquark molecules, $J^{P}=1/2^{-}$~$D^{ast}Xi_{cc}$ and $J^{P}=5/2^{-}$~$D^{ast}Xi_{cc}^{ast}$. In the baryon-baryon system, there exist seven di-baryon molecules, $J^{PC}=0^{-+}$~$bar{Xi}_{cc}Xi_{cc}$, $J^{PC}=1^{--}$~$bar{Xi}_{cc}Xi_{cc}$, $J^{PC}=1^{-+}$~$bar{Xi}_{cc}Xi_{cc}^{ast}$, $J^{PC}=1^{--}$~$bar{Xi}_{cc}Xi_{cc}^{ast}$, $J^{PC}=2^{-+}$~$bar{Xi}_{cc}Xi_{cc}^{ast}$, $J^{PC}=2^{-+}$~$bar{Xi}_{cc}^{ast}Xi_{cc}^{ast}$ and $J^{PC}=3^{--}$~$bar{Xi}_{cc}^{ast}Xi_{cc}^{ast}$. Among them, the $J^{PC}=0^{-+}$~$bar{Xi}_{cc}Xi_{cc}$ and/or $J^{PC}=1^{--}$~$bar{Xi}_{cc}Xi_{cc}$ molecules may contribute to the $X(7200)$ state recently observed by the LHCb Collaboration, which implies that $X(7200)$ can be related to $X(3872)$ via HADS. As a byproduct, with the heavy quark flavor symmetry we also study likely existence of molecular states in the $B^{(ast)}bar{B}^{(ast)}$, $bar{B}^{(ast)}Xi_{bb}^{(ast)}$, and $bar{Xi}_{bb}^{(ast)}Xi_{bb}^{(ast)}$ systems.
Inspired by the newly observed state $X^{*}(3860)$, we analyze the strong decay behaviors of some charmonium-like states $X^{*}(3860)$,$X(3872)$, $X(3915)$, $X(3930)$ and $X(3940)$ by the $^{3}P_{0}$ model. We carry out our work based on the hypothesis that these states are all being the charmonium systems. Our analysis indicates that $0^{++}$ charmonium state can be a good candidate for $X^{*}(3860)$ and $1^{++}$ state is the possible assignment for $X(3872)$. Considering as the $3^{1}S_{0}$ state, the decay behavior of $X(3940)$ is inconsistent with the experimental data. So, we can not assign $X(3940)$ as the $3^{1}S_{0}$ charmonium state by present work. Besides, our analysis imply that it is reasonable to assign $X(3915)$ and $X(3930)$ to be the same state, $2^{++}$. However, combining our analysis with that of Zhou~cite{ZhouZY}, we speculate that $X(3915)$/$X(3930)$ might not be a pure $coverline{c}$ systems.
In this work, we revisit the isospin violating decays of $X(3872)$ in a coupled-channel effective field theory. In the molecular scheme, the $X(3872)$ is interpreted as the bound state of $bar{D}^{*0}D^0/bar{D}^0D^{*0}$ and $D^{*-}D^+/D^-D^{*+}$ channels. In a cutoff-independent formalism, we relate the coupling constants of $X(3872)$ with the two channels to the molecular wave function. The isospin violating decays of $X(3872)$ are obtained by two equivalent approaches, which amend some deficiencies about this issue in literature. In the quantum field theory approach, the isospin violating decays arise from the coupling constants of $X(3872)$ to two di-meson channels. In the quantum mechanics approach, the isospin violating is attributed to wave functions at the origin. We illustrate that how to cure the insufficient results in literature. Within the comprehensive analysis, we bridge the isospin violating decays of $X(3872)$ to its inner structure. Our results show that the proportion of the neutral channel in $X(3872)$ is over $80%$. As a by-product, we calculate the strong decay width of $X(3872)to bar{D}^0 D^0pi^0$ and radiative one $X(3872)to bar{D}^0 D^0gamma$. The strong decay width and radiative decay width are about 30 keV and 10 keV, respectively, for the binding energy from $-300$ keV to $-50$ keV.
I review the experimental evidence for the $X(3915)$, the candidate nonstandard meson associated with $omega Jpsi$ resonance-like peaks in $Brightarrow Komega Jpsi$ and $gammagammarightarrowomega Jpsi$ near $M(omega Jpsi)=3920$~MeV, and address the conjecture that it can be identified as the $chi_{c2}^prime$, the radial excitation of the $chi_{c2}$ charmonium state. Since the partial decay width for $Brightarrow K X(3915)$ is at least an order-of-magnitude larger than that for $Brightarrow Kchi_{c2}$, its assignment as the $chi_{c2}^prime$ is dubious.
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