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arXiv 1609.01889hep-lathep-exhep-phnucl-th
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格点量子色动力学中$Λ$重子的味结构：从奇异夸克到粲夸克

Flavor structure of $Λ$ baryons from lattice QCD: From strange to charm quarks

Philipp Gubler, Toru T. Takahashi, Makoto Oka

备注：
14 pages, 8 figures, 5 tables; v2 (published version in PRD): title slightly changed, discussion about systematic uncertainties extended, typos fixed, references added
发表信息：
Phys. Rev. D 94, 114518 (2016)
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摘要：

在全2+1味格点量子色动力学中研究了具有奇异价夸克和粲价夸克的自旋宇称$\frac{1}{2}^{\pm}$重子。采用多个$SU(3)$单重态和八重态算符在晶格上产生所需的单重子态。通过变分方法，这些状态的耦合到不同的运营商提供的信息的味道结构的$Λ$重子。我们利用PACS-CS协作的规范配置和手性外推的质量和$SU(3)$味成分的物理点的结果。我们进一步将最重夸克的跃迁参数从奇异夸克逐渐改变到粲夸克，研究了$Λ$重子的性质随重夸克质量的变化。发现重子能级随夸克质量几乎呈线性增加。同时，大多数状态的风味结构保持稳定，除了最低的$\frac{1}{2}^{-}$状态，其从风味单线态$Λ$变为具有相当大小的单线态和八重态组分的$Λ_c$状态。最后，我们讨论了我们的发现是否可以用一个简单的夸克模型来解释，发现负宇称$Λ_c$态可以自然地解释为轻$u$和$d$夸克的双夸克激发。另一方面，夸克模型图像似乎不适合负宇称$Λ$态，这表明其他自由度来描述它们的重要性。

英文摘要：

We study $Λ$ baryons of spin-parity $\frac{1}{2}^{\pm}$ with either a strange or charm valence quark in full 2+1 flavor lattice QCD. Multiple $SU(3)$ singlet and octet operators are employed to generate the desired single baryon states on the lattice. Via the variational method, the couplings of these states to the different operators provide information about the flavor structure of the $Λ$ baryons. We make use of the gauge configurations of the PACS-CS Collaboration and chirally extrapolate the results for the masses and $SU(3)$ flavor components to the physical point. We furthermore gradually change the hopping parameter of the heaviest quark from strange to charm to study how the properties of the $Λ$ baryons evolve as a function of the heavy quark mass. It is found that the baryon energy levels increase almost linearly with the quark mass. Meanwhile, the flavor structure of most of the states remains stable, with the exception of the lowest $\frac{1}{2}^{-}$ state, which changes from a flavor singlet $Λ$ to a $Λ_c$ state with singlet and octet components of comparable size. Finally, we discuss whether our findings can be interpreted with the help of a simple quark model and find that the negative-parity $Λ_c$ states can be naturally explained as diquark excitations of the light $u$ and $d$ quarks. On the other hand, the quark-model picture does not appear to be adequate for the negative-parity $Λ$ states, suggesting the importance of other degrees of freedom to describe them.

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