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arXiv 1810.10550hep-lathep-phnucl-th
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格点量子色动力学中粲底四夸克态和重-轻四夸克态质量依赖性的证据

Evidence for charm-bottom tetraquarks and the mass dependence of heavy-light tetraquark states from lattice QCD

Anthony Francis, Renwick J. Hudspith, Randy Lewis, Kim Maltman

备注：
24 pages, 4 figures
发表信息：
Phys. Rev. D 99, 054505 (2019)
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摘要：

我们继续对重轻四夸克态的研究，从格点量子色动力学中发现了强相互作用稳定的$I(J^P)=0(1^+)$ $ud\bar{c}\bar{b}$四夸克态存在的证据，其质量在$\bar{D}B^*$阈值以下15 ~ 61 MeV.由于这个范围包括电磁$\bar{D}Bγ$衰减阈值，目前的不确定性不允许我们确定这样的状态是否会电磁衰减，或者只是微弱的衰减。我们还进行了研究，在固定的介子质量，与NRQCD的重夸克，模拟$qq^\prime \bar{b}^\prime \bar{b}$和$q q^\prime \bar{b}^\prime\bar{b}^\prime$四夸克态与$q,\, q^\prime =ud$或$\ell s$和可变的，非物理的$m_{b^\prime}$，以研究重质量依赖的四夸克态。我们发现，结合能的依赖遵循现象学预期的形式，虽然NRQCD打破$m_{b^\prime}=m_c$之前达到，在较高的$m_{b^\prime}$的结果清楚地确定了$ud\bar{b}^\prime \bar{b}$通道作为最有可能支持强相互作用稳定的四夸克态在$m_{b^\prime}=m_c$。该观察结果用于激励直接$ud\bar{c}\bar{b}$模拟。在整个过程中，我们使用的动力学$n_f=2+1$合奏与介子质量$m_π=$ 415，299和164 MeV几乎达到了物理点，一个相对论重夸克的魅力夸克处方，和NRQCD底夸克（s）。

英文摘要：

We continue our study of heavy-light four-quark states and find evidence from lattice QCD for the existence of a strong-interaction-stable $I(J^P)=0(1^+)$ $ud\bar{c}\bar{b}$ tetraquark with mass in the range of 15 to 61 MeV below $\bar{D}B^*$ threshold. Since this range includes the electromagnetic $\bar{D}Bγ$ decay threshold, current uncertainties do not allow us to determine whether such a state would decay electromagnetically, or only weakly. We also perform a study at fixed pion mass, with NRQCD for the heavy quarks, simulating $qq^\prime \bar{b}^\prime \bar{b}$ and $q q^\prime \bar{b}^\prime\bar{b}^\prime$ tetraquarks with $q,\, q^\prime =ud$ or $\ell s$ and variable, unphysical $m_{b^\prime}$ in order to investigate the heavy mass-dependence of such tetraquark states. We find that the dependence of the binding energy follows a phenomenologically-expected form and that, though NRQCD breaks down before $m_{b^\prime}=m_c$ is reached, the results at higher $m_{b^\prime}$ clearly identify the $ud\bar{b}^\prime \bar{b}$ channel as the most likely to support a strong-interaction-stable tetraquark state at $m_{b^\prime}=m_c$. This observation serves to motivate the direct $ud\bar{c}\bar{b}$ simulation. Throughout we use dynamical $n_f=2+1$ ensembles with pion masses $m_π=$415, 299, and 164 MeV reaching down almost to the physical point, a relativistic heavy quark prescription for the charm quark, and NRQCD for the bottom quark(s).

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