This paper reports the study of D+s→τ+ν via τ+→π+¯ντ using a boosted decision tree method, with 7.33 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between ...4.128 and 4.226 GeV. The branching fraction of D+s→τ+ντ is determined to be (5.44±0.17stat±0.13syst)%. The product of the D+s decay constant fD+s and the Cabibbo-Kobayashi-Maskawa matrix element |Vcs| is fD+s|Vcs|=(248.3±3.9stat±3.1syst±1.0input) MeV. Combining with the |Vcs| value obtained from the Standard Model global fit or the fD+s from the lattice quantum chromodynamics, we determine |Vcs|=0.993±0.015stat±0.012syst±0.004input and fD+s=(255.0±4.0stat±3.2syst±1.0input) MeV. The first uncertainty is statistical, the second one is systematic and the third one is due to the input parameters, mainly the lifetime of D+s. All results obtained in this work supersede the BESIII previous results based on 6.32 fb−1 of e+e− collision data taken at center-of-mass energies between 4.178 and 4.226 GeV.
Precision measurements of the semileptonic decays D+s→ηe+νe and D+s→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(D+s→ηe+νe)=(2.255±0.039stat±0.051syst)% and B(D+s→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 D+s→ηe+νe and D+s→η′e+νe, the products of the hadronic transition form factors fη(')+(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 fη+(0)|Vcs|=0.4519±0.0071stat±0.0065syst and fη′+(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.
A narrow structure in the pΛover ¯ system near the mass threshold, named as X(2085), is observed in the process e^{+}e^{-}→pK^{-}Λover ¯ with a statistical significance greater than 20σ. Its spin and ...parity are determined for the first time to be J^{P}=1^{+} in an amplitude analysis, with a statistical significance greater than 5σ over other quantum numbers (0^{-},1^{-} and 2^{+}). The pole positions of X(2085) are measured to be M_{pole}=(2084_{-2}^{+4}±9) MeV and Γ_{pole}=(58_{-3}^{+4}±25) MeV, where the first uncertainties are statistical and the second ones are systematic. The analysis is based on the study of the process e^{+}e^{-}→pK^{-}Λover ¯ and uses the data samples collected with the BESIII detector at the center-of-mass energies sqrts=4.008, 4.178, 4.226, 4.258, 4.416, and 4.682 GeV with a total integrated luminosity of 8.35 fb^{-1}.
