Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands.
Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
Phys Rev Lett. 2018 Aug 17;121(7):072002. doi: 10.1103/PhysRevLett.121.072002.
From samples of pp collision data collected by the LHCb experiment at sqrt[s]=7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb^{-1}, respectively, a peak in both the Λ_{b}^{0}K^{-} and Ξ_{b}^{0}π^{-} invariant mass spectra is observed. In the quark model, radially and orbitally excited Ξ_{b}^{-} resonances with quark content bds are expected. Referring to this peak as Ξ_{b}(6227)^{-}, the mass and natural width are measured to be m_{Ξ_{b}(6227)^{-}}=6226.9±2.0±0.3±0.2 MeV/c^{2} and Γ_{Ξ_{b}(6227)^{-}}=18.1±5.4±1.8 MeV/c^{2}, where the first uncertainty is statistical, the second is systematic, and the third, on m_{Ξ_{b}(6227)^{-}}, is due to the knowledge of the Λ_{b}^{0} baryon mass. Relative production rates of the Ξ_{b}(6227)^{-}→Λ_{b}^{0}K^{-} and Ξ_{b}(6227)^{-}→Ξ_{b}^{0}π^{-} decays are also reported.
从 LHCb 实验在 sqrt[s]=7、8 和 13 TeV 下收集的 pp 碰撞数据样本中，分别对应于 1.0、2.0 和 1.5 fb^{-1}的积分亮度，在 Λ_{b}^{0}K^{-}和 Ξ_{b}^{0}π^{-}不变质量谱中观察到一个峰。在夸克模型中，预计存在具有 bds 夸克内容的径向和轨道激发的 Ξ_{b}^{-}共振。将这个峰称为 Ξ_{b}(6227)^{-}，测量到它的质量和自然宽度分别为 m_{Ξ_{b}(6227)^{-}}=6226.9±2.0±0.3±0.2 MeV/c^{2} 和 Γ_{Ξ_{b}(6227)^{-}}=18.1±5.4±1.8 MeV/c^{2}，其中第一个不确定度是统计的，第二个是系统的，第三个，关于 m_{Ξ_{b}(6227)^{-}}，是由于 Λ_{b}^{0}重子质量的知识。还报道了 Ξ_{b}(6227)^{-}→Λ_{b}^{0}K^{-}和 Ξ_{b}(6227)^{-}→Ξ_{b}^{0}π^{-}衰变的相对产生率。
