First measurements of the branching fractions for the decay modes Ξ0 c → Λη and Ξ0 c → Λη0 and search for the decay Ξ0 c → Λπ0 using Belle and Belle II data

Using data samples of 988.4 fb−1 and 427.9 fb−1 collected with the Belle and Belle II detectors, we present a study of the singly Cabibbo-suppressed decays Ξ0c → Λη, Λη0, and Λπ0. We observe the decay Ξ0c → Λη and find evidence for the decay Ξ0c → Λη0, with corresponding branching ratios determined to be ℬ⁡(Ξ0 𝑐→Λ⁢𝜂)/ℬ⁡(Ξ0 𝑐→Ξ−⁢𝜋+) =(4.16 ±0.91 ±0.23)% and ℬ⁡(Ξ0𝑐→Λ⁢𝜂′)/ℬ⁡(Ξ0𝑐→Ξ−⁢𝜋+) = (2.48 ±0.82 ±0.12)%, respectively. We find no significant signal in the Ξ0c → Λπ0 decay mode and set an upper limit at the 90% credibility level of ℬ⁡(Ξ0𝑐→Λ⁢𝜋0)/ℬ⁡(Ξ0𝑐→Ξ−⁢𝜋+) <3.5%. Multiplying these ratios by the world-average branching fraction of the normalization channel, ℬ⁡(Ξ0𝑐 →Ξ−⁢𝜋+) =(1.43 ±0.27)%, we obtain the absolute branching fractions of ℬ⁡(Ξ0𝑐 →Λ⁢𝜂) = (5.95 ±1.30 ±0.32 ±1.13) ×10−4, ℬ⁡(Ξ0𝑐 →Λ⁢𝜂′) =(3.55 ±1.17 ±0.17 ±0.68) ×10−4, and an upper limit at the 90% credibility level on the absolute branching fraction of ℬ⁡(Ξ0𝑐 →Λ⁢𝜋0) <5.2 ×10−4. The quoted first and second uncertainties are statistical and systematic, respectively, while the third uncertainties arise from the branching fraction of the normalization mode. These results are consistent with most theoretical predictions and further the understanding of the underlying decay mechanisms.