Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions, and allow searches for physics beyond the Standard Model. We present the first results on isospin amplitudes in $b$-baryon decays, using data corresponding to an integrated luminosity of 8.5 fb${}^{-1}$, collected with the LHCb detector in $pp$ collisions at center of mass energies of 7, 8 and 13 TeV. The isospin amplitude ratio $|A_1({\Lambda }_b^0\to J/\psi {\Sigma }^0)/A_0({\Lambda }_b^0\to J/\psi \Lambda )|$, where the subscript on $A$ indicates the final-state isospin, is measured to be less than $1/20.9$ at 95% confidence level. The Cabibbo suppressed ${\Xi }_b^0\to J/\psi \Lambda$ decay is observed for the first time, allowing for the measurement $|A_0({\Xi }_b^0\to J/\psi \Lambda )/A_{1/2}({\Xi }_b^0\to J/\psi {\Xi }^0)|=0.44\pm 0.06\pm 0.02$, where the uncertainties are statistical and systematic, respectively.

中文翻译：

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pinb0→J /ψΛ（Σ0）和Ξb0→J /ψΞ0（Λ）衰减时的同位旋振幅

强子衰变中的等位旋振幅比是探讨弱相互作用和强相互作用之间相互作用的有用方法，并允许在标准模型之外进行物理研究。我们提出了关于等位旋振幅的第一个结果$b$-重子衰减，使用的数据对应于8.5 fb的综合亮度${}^{-\mathrm{1个}}$，由LHCb检测器收集在 $pp$在7、8和13 TeV的质能中心发生碰撞。同位旋振幅比$|{\mathrm{一种}}_{\mathrm{1个}}（{\Lambda }_b^0\to Ĵ/\psi {\Sigma }^0）/{\mathrm{一种}}_0（{\Lambda }_b^0\to Ĵ/\psi \Lambda ）|$，其中下标位于 $\mathrm{一种}$ 指示最终状态的同位旋，被测量为小于 $\mathrm{1个}/20.9$置信水平为95％。Cabibbo被压制${\Xi }_b^0\to Ĵ/\psi \Lambda$ 第一次观察到衰减，可以进行测量 $|{\mathrm{一种}}_0（{\Xi }_b^0\to Ĵ/\psi \Lambda ）/{\mathrm{一种}}_{\mathrm{1个}/2}（{\Xi }_b^0\to Ĵ/\psi {\Xi }^0）|=0.44\pm 0.06\pm 0.02$，其中不确定性分别是统计的和系统的。