为什么$Ξ(1690)$和$Ξ(2120)$如此狭窄？
Why $Ξ(1690)$ and $Ξ(2120)$ are so narrow?
摘要：
与非奇异重子和奇异重子相比，$Ξ$重子自然地更窄，因为它们只有一个轻夸克，因此，它们的衰变要么产生一个轻介子和双奇异重子，要么产生具有奇异性的介子和重子，这涉及相对更多的能量。事实上，当某些$Ξ$具有大的相空间以衰减到某些开放通道时，它们的全宽度甚至为10-20 MeV的量级。这就是$Ξ(1690)$的情况，在最新的{ \it BABAR}和BELLE数据中发现其宽度为10 MeV的量级。在这篇手稿中，我们研究为什么有些$Ξ$的是如此狭窄。基于具有手征和隐定域对称性拉格朗日量的赝标介子-重子和矢量介子-重子系统的耦合通道计算，我们发现答案在于复杂的强子动力学。我们发现$Ξ(1690)$已知的质量、宽度、自旋宇称和分支比都可以用耦合道介子-重子动力学自然地解释。我们发现了另一个窄共振，这可能与$Ξ(2120)$。我们还寻找奇异态$Ξ^{+}$和$Ξ^{--}$，但没有发现。此外，我们还提供了$ \bar K Λ, \bar K Σ\rightarrow πΞ$的截面，这对于理解最近重离子碰撞研究中报道的$Ξ$的产额增加是有用的。
英文摘要：
The $Ξ$ baryons are expected to be naturally narrower as compared to their nonstrange and strange counterparts since they have only one light quark and, thus, their decay involves producing either a light meson and doubly strange baryon or both meson and baryon with strangeness which involves, relatively, more energy. In fact, some $Ξ$'s have full widths of the order of even 10-20 MeV when, in principle, they have a large phase space to decay to some open channels. Such is the case of $Ξ(1690)$, for which the width has been found to be of the order of 10 MeV in the latest {\it BABAR} and BELLE data. In this manuscript we study why some $Ξ$'s are so narrow. Based on a coupled channel calculation of the pseudoscalar meson-baryon and vector meson-baryon systems with chiral and hidden local symmetry Lagrangians, we find that the answer lies in the intricate hadron dynamics. We find that the known mass, width, spin-parity and branching ratios of $Ξ(1690)$ can be naturally explained in terms of coupled channel meson-baryon dynamics. We find another narrow resonance which can be related to $Ξ(2120)$. We also look for exotic states $Ξ^{+}$ and $Ξ^{--}$ but find none. In addition we provide the cross sections for $ \bar K Λ, \bar K Σ\rightarrow πΞ$ which can be useful for understanding the enhanced yield of $Ξ$ reported in recent studies of heavy ion collisions.
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