No abstract

No abstract

No abstract

We report the first measurement of the absolute branching fraction for Λ + c → Λe + νe. This measurement is based on 567 pb −1 of e + e − annihilation data produced at √ s = 4.599 GeV, 116 which is just above the Λ + cΛ − c threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be B(Λ + c → Λe + νe) = 118(3.63±0.38(stat)±0.20(syst))%, representing a significant improvement in precision over the current indirect determination. As the branching fraction for Λ + c → Λe + νe is the benchmark for those of 120 other Λ + c semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.

Using a data sample corresponding to an integrated luminosity of 2.93 fb −1 recorded by the BESIII detector at a center-of-mass energy of 3.773 GeV, we present an analysis of the decays D 0 →π − π 0 e þ ν e and D þ → π − π þ e þ ν e. By performing a partial wave analysis, the π þ π − S-wave contribution to D þ → π − π þ e þ ν e is observed to be ð25.7 AE 1.6 AE 1.1Þ% with a statistical significance greater than 10σ, besides the dominant P-wave contribution. This is the first observation of the S-wave contribution. We measure the branching fractions BðD 0 →ρ − e þ ν e Þ¼ð1.445AE0.058AE0.039Þ×10 −3 , BðD þ →ρ 0 e þ ν e Þ¼ ð1.860AE0.070AE0.061Þ×10 −3 , and B(D þ →f 0 ð500Þe þ ν e ;f 0 ð500Þ→π þ π −)¼ð6.30AE0.43AE0.32Þ×10 −4. An upper limit of B(D þ → f 0 ð980Þe þ ν e ; f 0 ð980Þ → π þ π −) < 2.8 × 10 −5 is set at the 90% confidence level. We also obtain the hadronic form factor ratios of D → ρe þ ν e at q 2 ¼ 0 assuming the single-pole dominance parametrization: r V ¼ f½Vð0Þ=½A 1 ð0Þg ¼ 1.695 AE 0.083 AE 0.051, r 2 ¼ f½A 2 ð0Þ=½A 1 ð0Þg ¼ 0.845 AE 0.056 AE 0.039.