Abstract The isovector and isoscalar ND s-wave scattering lengths are extracted by fitting to the LHCb data of the p D 0 invariant-mass distribution in the decay Λ b → π − p D 0 , making use of the cusp effect at the n D + threshold. The analysis is based on a coupled-channel nonrelativistic effective field theory. We find that the real part of the isovector ND scattering length is unnaturally large due to the existence of a near-threshold state with a mass around 2.8 GeV. The state is consistent with the Σ c ( 2800 ) + resonance observed at Belle. Our results suggest that it couples strongly to the ND channel in an s-wave, and that its quantum numbers are J P = 1 / 2 − . The strong cusp behavior at the n D + threshold can be verified using updated LHCb data.

中文翻译：

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从 Λ → π−pD0 衰减和 Σ (2800)+ 的性质中提取 ND 散射长度

摘要 通过拟合衰减Λ b → π − p D 0 中p D 0 不变质量分布的LHCb 数据，利用n D 处的尖点效应，提取等向量和等标ND s 波散射长度+ 阈值。该分析基于耦合通道非相对论有效场理论。我们发现，由于存在质量约为 2.8 GeV 的近阈值状态，等向量 ND 散射长度的实部异常大。该状态与在 Belle 观察到的 Σ c ( 2800 ) + 共振一致。我们的结果表明它与 s 波中的 ND 通道强烈耦合，并且其量子数为 JP = 1 / 2 - 。可以使用更新的 LHCb 数据验证 n D + 阈值处的强尖峰行为。