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Institute of High Energy Physics, Beijing 100049, People's Republic of China.
G. I. Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia.
Phys Rev Lett. 2022 Apr 8;128(14):142001. doi: 10.1103/PhysRevLett.128.142001.
The singly Cabibbo-suppressed decay Λ_{c}^{+}→nπ^{+} is observed for the first time with a statistical significance of 7.3σ by using 3.9 fb^{-1} of e^{+}e^{-} collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ_{c}^{+}→nπ^{+} is measured to be (6.6±1.2_{stat}±0.4_{syst})×10^{-4}. By taking the upper limit of branching fractions of Λ_{c}^{+}→pπ^{0} from the Belle experiment, the ratio of branching fractions between Λ_{c}^{+}→nπ^{+} and Λ_{c}^{+}→pπ^{0} is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with most predictions of the available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ_{c}^{+}→Λπ^{+} and Λ_{c}^{+}→Σ^{0}π^{+} are measured to be (1.31±0.08_{stat}±0.05_{syst})×10^{-2} and (1.22±0.08_{stat}±0.07_{syst})×10^{-2}, respectively, which are consistent with previous results.
利用北京正负电子对撞机（BEPCII）上的北京谱仪III（BESIII）探测器，在质心能量为4.612至4.699 GeV之间收集的3.9 fb⁻¹的e⁺e⁻碰撞数据，首次观测到单卡比博压低衰变Λc⁺→nπ⁺，统计显著性为7.3σ。测得Λc⁺→nπ⁺的分支比为(6.6±1.2统计±0.4系统)×10⁻⁴。根据 Belle 实验给出的Λc⁺→pπ⁰分支比上限，在90%置信水平下计算出Λc⁺→nπ⁺与Λc⁺→pπ⁰的分支比之比大于7.2，这与现有唯象模型的大多数预测不一致。此外，测得卡比博允许衰变Λc⁺→Λπ⁺和Λc⁺→Σ⁰π⁺的分支比分别为(1.31±0.08统计±0.05系统)×10⁻²和(1.22±0.08统计±0.07系统)×10⁻²，与先前结果一致。
