Precision measurements of Ds+ →ηe+νe and Ds+ →η′e+νe

Precision measurements of the semileptonic decays Ds+→ηe+νe and Ds+→η′e+νe are performed with 7.33 fb-1 of e+e- collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector. The branching fractions obtained are B(Ds+→ηe+νe)=(2.255±0.039stat±0.051syst)% and B(Ds+→η′e+νe)=(0.810±0.038stat±0.024syst)%. Combining these results with the B(D+→ηe+νe) and B(D+→η′e+νe) obtained from previous BESIII measurements, the η-η′ mixing angle in the quark flavor basis is determined to be φP=(40.0±2.0stat±0.6syst)°. Moreover, from the fits to the partial decay rates of Ds+→ηe+νe and Ds+→η′e+νe, the products of the hadronic transition form factors f+η(′)(0) and the modulus of the c→s Cabibbo-Kobayashi-Maskawa matrix element |Vcs| are determined by using different hadronic transition form factor parametrizations. Based on the two-parameter series expansion, the products f+η(0)|Vcs|=0.4519±0.0071stat±0.0065syst and f+η′(0)|Vcs|=0.525±0.024stat±0.009syst are extracted. All results determined in this work supersede those measured in the previous BESIII analyses based on the 3.19 fb-1 subsample of data at 4.178 GeV.