X线的第二行（3872）
Line Shapes of the X(3872)
摘要：
如果X（3872）的量子数是J^{PC}=1^{++}，那么对它的质量的测量就意味着它要么是一个松散束缚的强子分子，其成分是粲介子对D^{*0} Dbar ^{*0}和D^0 Dbar^{*0}的叠加，要么是这些粲介子的虚态。它的结合能足够小，以至于组分D^{*0}或Dbar^{*0}的衰变宽度对X共振的线形有显著影响。我们发展了一个简单的近似线的形状，考虑到D^{*0}宽度的影响，以及非弹性散射的魅力介子的通道。我们同时拟合了贝尔合作组织在B^+到K^+ + X衰变中测量的J/psi π ^+ π ^-和D^0 Dbar^0 π ^0通道中的线形。最佳拟合对应于X（3872）是刚好低于D^{*0} Dbar^0阈值的束缚态，但不排除刚好高于D^{*0} D-ar^0阈值的虚态。
英文摘要：
If the quantum numbers of the X(3872) are J^{PC}=1^{++}, the measurement of its mass implies that it is either a loosely-bound hadronic molecule whose constituents are a superposition of the charm mesons pairs D^{*0} Dbar^0 and D^0 Dbar^{*0} or else it is a virtual state of these charm mesons. Its binding energy is small enough that the decay width of a constituent D^{*0} or Dbar^{*0} has a significant effect on the line shapes of the X resonance. We develop a simple approximation to the line shapes that takes into account the effect of the D^{*0} width as well as inelastic scattering channels of the charm mesons. We carry out a simultaneous fit to the line shapes in the J/psi pi^+ pi^- and D^0 Dbar^0 pi^0 channels measured in the decays B^+ to K^+ + X by the Belle Collaboration. The best fit corresponds to the X(3872) being a bound state just below the D^{*0} Dbar^0 threshold, but a virtual state just above the D^{*0} D-ar^0 threshold is not excluded.
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