Measurements of the Branching Fractions of the Semileptonic Decays Ξ 0 c → Ξ − ℓ + ν ℓ and the Asymmetry Parameter of Ξ 0 c → Ξ − π +

Abstract

Using data samples of 89.5 and 711 fb−1 recorded at energies of ffiffi s p ¼ 10.52 and 10.58 GeV, respectively, with the Belle detector at the KEKB eþe− collider, we report measurements of branching fractions of semileptonic decays Ξ0 c → Ξ−lþνl (l ¼ e or μ) and the CP-asymmetry parameter of Ξ0 c → Ξ−πþ decay. The branching fractions are measured to be BðΞ0 c → Ξ−eþνeÞ¼ð1.31 0.04 0.07 0.38Þ% and BðΞ0 c → Ξ−μþνμÞ¼ð1.27 0.06 0.10 0.37Þ%, and the decay parameter αΞπ is measured to be 0.63 0.03 0.01 with much improved precision compared with the current world average. The corresponding ratio BðΞ0 c → Ξ−eþνeÞ=BðΞ0 c → Ξ−μþνμÞ is 1.03 0.05 0.07, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter ACP ¼ ðαΞ−πþ þ αΞ¯ þπ− Þ=ðαΞ−πþ − αΞ¯ þπ− Þ ¼ 0.024 0.052 0.014 is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the Ξ0 c → Ξ−πþ branching fraction.