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Institute
By analyzing 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, we search for the semileptonic decays D+s→K1(1270)0e+νe and D+s→b1(1235)0e+νe for the first time. No significant signals are observed for either decay mode. The upper limits on the (product) branching fractions are determined to be B[D+s→K1(1270)0e+νe]<4.1×10−4 and B[D+s→b1(1235)0e+νe]⋅B[b1(1235)0→ωπ0]<6.4×10−4 at 90\% confidence level.
Based on a sample of (448.1±2.9)×106 𝜓(3686) events collected with the BESIII detector at BEPCII, the decays of 𝜓(3686)→𝐾−Λ¯Ξ++c.c. with ¯Ξ+→¯Λ𝜋+, ¯Λ→¯𝑝𝜋+ are studied. We investigate the two excited resonances, Ξ(1690)− and Ξ(1820)−, which are each observed with large significance (≫10𝜎) in the 𝐾−Λ invariant mass distributions. A partial wave analysis is performed, and the spin-parities of Ξ(1690)− and Ξ(1820)− are measured to be 12− and 32−, respectively. The masses, widths, and product branching fractions of Ξ(1690)− and Ξ(1820)− are also measured.
Based on (2712.4±14.3)×106 events recorded at the 𝜓(3686) nominal mass collected with the BESIII detector operating at the BEPCII collider, the 𝜓(3686)→Σ+¯Σ−𝜔 and Σ+¯Σ−𝜙 decays are observed for the first time with statistical significances of 13.8𝜎 and 7.6𝜎, respectively. The corresponding branching fractions are measured to be ℬ(𝜓(3686)→Σ+¯Σ−𝜔)=(1.89±0.18±0.21)×10−5 and ℬ(𝜓(3686)→Σ+¯Σ−𝜙)=(2.96±0.54±0.41)×10−6, where the first uncertainties are statistical and the second systematic.
Using a sample of (27.12±0.14)×108 ψ(3686) events collected with the BESIII detector, the decay ψ(3686)→ΛΛ¯η′ with η′ subsequently decaying into γπ+π− and ηπ+π− is observed for the first time. The branching fraction of ψ(3686)→ΛΛ¯η′ is measured to be (7.34±0.94(stat.)±0.43(sys.))×10−6. No resonant structures are evident in the Λη′, Λ¯η′ and ΛΛ¯ mass spectra.
Measurement of e⁺e⁻ → ΛΛ¯η from 3.5106 to 4.6988 GeV and study of ΛΛ¯ mass threshold enhancement
(2022)
Using data samples with a total integrated luminosity of approximately 18 fb−1 collected by the BESIII detector operating at the BEPCII, the process e+e−→ΛΛ¯η is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process e+e−→ΛΛ¯η is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the ΛΛ¯ mass threshold is observed for the first time in the process. The structure can be described by an S-wave Breit-Wigner function. Neglecting contribution of excited Λ states and potential interferences, the mass and width are determined to be (2356±7±17) MeV/c2 and (304±28±54) MeV, respectively, where the first uncertainties are statistical and the second are systematic.
Measurement of e⁺e⁻ → ΛΛ¯η from 3.5106 to 4.6988 GeV and study of ΛΛ¯ mass threshold enhancement
(2022)
Using data samples with a total integrated luminosity of approximately 18 fb−1 collected by the BESIII detector operating at the BEPCII, the process e+e−→ΛΛ¯η is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process e+e−→ΛΛ¯η is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the ΛΛ¯ mass threshold is observed for the first time in the process. The structure can be described by an S-wave Breit-Wigner function. Neglecting contribution of excited Λ states and potential interferences, the mass and width are determined to be (2356±7±17) MeV/c2 and (304±28±54) MeV, respectively, where the first uncertainties are statistical and the second are systematic.
We perform a study of the X(3872) lineshape using the data samples of e+e−→γX(3872), X(3872)→D0D¯0π0 and π+π−J/ψ collected with the BESIII detector. The effects of the coupled-channels and the off-shell D∗0 are included in the parameterization of the lineshape. The lineshape mass parameter is obtained to be MX=(3871.63±0.13+0.06−0.05) MeV. Two poles are found on the first and second Riemann sheets corresponding to the D∗0D¯0 branch cut. The pole location on the first sheet is much closer to the D∗0D¯0 threshold than the other, and is determined to be 7.04±0.15+0.07−0.08 MeV above the D0D¯0π0 threshold with an imaginary part −0.19±0.08+0.14−0.19 MeV.
By analyzing 7.33 fb−1 of e+e− annihilation data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we report the observation of the semileptonic decay D+s→η′μ+νμ, with a statistical significance larger than 10σ, and the measurements of the D+s→ημ+νμ and D+s→η′μ+νμ decay dynamics for the first time. The branching fractions of D+s→ημ+νμ and D+s→η′μ+νμ are determined to be (2.235±0.051stat±0.052syst)% and (0.801±0.055stat±0.028syst)%, respectively, with precision improved by factors of 6.0 and 6.6 compared to the previous best measurements. Combined with the results for the decays D+s→ηe+νe and D+s→η′e+νe, the ratios of the decay widths are examined both inclusively and in several ℓ+νℓ four-momentum transfer ranges. No evidence for lepton flavor universality violation is found within the current statistics. The products of the hadronic form factors fη(′)+,0(0) and the c→s Cabibbo-Kobayashi-Maskawa matrix element |Vcs| are determined. The results based on the two-parameter series expansion are fη+,0(0)|Vcs| = 0.452±0.010stat±0.007syst and fη′+,0(0)|Vcs| = 0.504±0.037stat±0.012syst, which help to constrain present models on fη(′)+,0(0). The forward-backward asymmetries are determined to be ⟨AηFB⟩=−0.059±0.031stat±0.005syst and ⟨Aη′FB⟩=−0.064±0.079stat±0.006syst for the first time, which are consistent with the theoretical calculation.
This paper reports the study of D+s→τ+ν via τ+→π+ν¯τ 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 CKM 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.
Precise measurement of the branching fractions of of J/ψ → Λ¯π⁺Σ⁻ + c.c. and J/ψ → Λ¯π⁻Σ⁺ + c.c.
(2023)
Based on a data sample of (10087±44)×106 J/ψ events collected with the BESIII detector, the branching fraction of J/ψ→Λ¯π+Σ−+c.c. is measured to be (1.221±0.002±0.038)×10−3, and the branching fraction of its isospin partner mode J/ψ→Λ¯π−Σ++c.c. is measured to be (1.244±0.002±0.045)×10−3 with improved precision. Here the first uncertainties are statistical and the second ones systematic. The isospin symmetry of the Σ baryon in charmonium hadronic decay and the "12% rule" are tested, and no violation is found. The potential of using these channels as Σ baryon sources for nuclear physics research is studied, and the momentum and angular distributions of these sources are provided.