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تسجيل مستخدم جديدInvestigating different structures for the $X(3872)$
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Using the QCD spectral sum rule approach we investigate different currents with $J^{PC}=1^{++}$, which could be associated with the $X(3872)$ meson. Our results indicate that, with a four-quark or molecular structure, it is very difficult to explain the narrow width of the state unless the quarks have a special color configuration.
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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 a
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In this paper we consider all possible 1D and 2P ccbar assignments for the recently discovered X(3872). Taking the experimental mass as input, we give numerical results for the E1 radiative widths as well as the three principal types of strong decays
; open-charm, ccbar annihilation and closed-charm hadronic transitions. We find that many assignments may be immediately eliminated due to the small observed total width. The remaining viable ccbar assignments are 3D3, 3D2, 1D2, 2 3P1 and 2 1P1. A search for the mode J/psi pi0 pi0 can establish the C-parity of the X(3872), which will eliminate many of these possibilities. Radiative transitions can then be used to test the remaining assignments, as they populate characteristic final states. The 3D2 and 1D2 states are predicted to have large (ca.50%) radiative branching fractions to chi_1 gamma and h_c gamma respectively. We predict that the 3D3 will also be relatively narrow and will have a significant (ca.10%) branching fraction to chi_2 gamma, and should also be observable in B decay. Tests for non-ccbar X(3872) assignments are also discussed.
It was recently proposed that the $X(3872)$ binding energy, the difference between the $D^0bar D^{*0}$ threshold and the $X(3872)$ mass, can be precisely determined by measuring the $gamma X(3872)$ line shape from a short-distance $D^{*0}bar D^{*0}$
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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 wou
ld 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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