标题： S波介子-反介子态中的重夸克自旋选择规则 显示英文标题

标题： Heavy quark spin selection rules in S-wave meson-antimeson states

摘要： 通过研究重夸克极限下S波介子-反介子系统的自旋结构，我们发现对于$c\bar{c}$自旋的$J_{c\bar{c}}$只有两个选择规则：(a)$J=min(J_\ell)-1$或$J=max(J_\ell)+1$；(b)$J^C=1^+,2^-,3^+,\cdots$如果两个介子不同但属于同一双重态。这里$J_\ell$是轻度自由度的总角动量。这些规则可能限制介子-反介子分子或共振态的衰变通道。 对于最近观测到的$Z_c(3900)$状态，如果它是一个$D\bar{D}^*$分子或共振态，原则上可以衰变为$J_{c\bar{c}}=0$重夸克onium通道。 未观测到$h_c\pi$衰变可能意味着该状态是四夸克态。 显示英文摘要

摘要： By studying the spin structure of an S-wave meson-antimeson system in the heavy quark limit, we find two selection rules for the $c\bar{c}$ spin $J_{c\bar{c}}$ being only 1: (a) $J=min(J_\ell)-1$ or $J=max(J_\ell)+1$; (b) $J^C=1^+,2^-,3^+,\cdots$ if the two mesons are different but belong to the same doublet. Here $J_\ell$ is the total angular momentum of the light degree of freedom. The rules may constrain decay channels of a meson-antimeson molecule or resonance. For the recently observed $Z_c(3900)$ state, it in principle can decay into $J_{c\bar{c}}=0$ charmonium channels if it is a $D\bar{D}^*$ molecule or resonance. The non-observation of $h_c\pi$ decay might imply that this state is a tetraquark.