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We present a study of the process e+e−→ηϕ using data samples collected with the BESIII detector corresponding to an integrated luminosity of 15.03 fb−1 at 23 center-of-mass energies from 3.773 to 4.600 GeV. The Born cross sections are measured at each energy and a coherent fit to cross-section lineshape is performed using a Breit-Wigner parametrization to search for charmonium-like vector states. No significant signals of the Y(4230) and Y(4360) resonances are observed.
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.
Evidence for the singly Cabibbo suppressed decay Λ+c→pπ0 is reported for the first time with a statistical significance of 3.7σ based on 6.0 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Λ+c→pπ0 is measured to be (1.56+0.72−0.58±0.20)×10−4. Combining with the branching fraction of Λ+c→nπ+, (6.6±1.3)×10−4, the ratio of the branching fractions of Λ+c→nπ+ and Λ+c→pπ0 is calculated to be 3.2+2.2−1.2. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Λ+c→pη is measured to be (1.63±0.31stat±0.11syst)×10−3.
Based on data samples collected with the BESIII detector at the BEPCII collider, the process e+e−→Σ+Σ¯− is studied at center-of-mass energies s√ = 2.3960, 2.6454, and 2.9000~GeV. Using a fully differential angular description of the final state particles, the complete information of the Σ+ electromagnetic form factors in the time-like region is extracted. The relative phase between the electric and magnetic form factors is determined to be sinΔΦ = -0.67~±~0.29~(stat.)~±~0.18~(syst.) at s√ = 2.3960~GeV, ΔΦ = 55∘~±~19∘~(stat.) ±~14∘~(syst.) at s√ = 2.6454~GeV, and 78∘~±~22∘~(stat.) ±~9∘~(syst.) at s√ = 2.9000~GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.
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 data set of (27.12±0.10)×108 ψ(3686) events collected at the BESIII experiment, the absolute branching fractions of the three dominant Ω− decays are measured to be BΩ−→Ξ0π−=(25.03±0.44±0.53)%, BΩ−→Ξ−π0=(8.43±0.52±0.28)%, and BΩ−→ΛK−=(66.3±0.8±2.0)%, where the first and second uncertainties are statistical and systematic, respectively. The ratio between BΩ−→Ξ0π− and BΩ−→Ξ−π0 is determined to be 2.97±0.19±0.11, which is in good agreement with the PDG value of 2.74±0.15, but greater by more than four standard deviations than the theoretical prediction of 2 obtained from the ΔI=1/2 rule.
The Born cross sections and effective form factors of the process 𝑒+𝑒−→Λ¯Σ0+c.c. are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of (478.5±4.8) pb−1 collected with the BESIII detector. A nonzero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BABAR Collaboration. The Born cross-section line shape is described better by a shape considering the strong-interaction effects than by a pQCD motivated functional form.
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.
The Born cross sections and effective form factors of the process e+e−→ΛΣ¯0+c.c. are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of (478.5±4.8) pb−1 collected with the BESIII detector. A non-zero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BaBar Collaboration. The Born cross-section lineshape is described better by a shape with a plateau near the threshold than by a pQCD motivated functional form.
The first observation of the decays J/ψ→p¯Σ+K0S and J/ψ→pΣ¯−K0S is reported using (10087±44)×106 J/ψ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of each channel are determined to be B(J/ψ→p¯Σ+K0S)=(1.361±0.006±0.025)×10−4 and B(J/ψ→pΣ¯−K0S)=(1.352±0.006±0.025)×10−4. The combined result is B(J/ψ→p¯Σ+K0S+c.c.)=(2.725±0.009±0.050)×10−4, where the first uncertainty is statistical and the second systematic. The results presented are in good agreement with the branching fractions of the isospin partner decay J/ψ→pK−Σ¯0+c.c..
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.
The process e+e−→D∗+sD∗−s is studied with a semi-inclusive method using data samples at center-of-mass energies from threshold to 4.95 GeV collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections of the process are measured for the first time with high precision in this energy region. Two resonance structures are observed in the energy-dependent cross sections around 4.2 and 4.4 GeV. By fitting the cross sections with a coherent sum of three Breit-Wigner amplitudes and one phase-space amplitude, the two significant structures are assigned masses of (4186.5±9.0±30) MeV/c2 and (4414.5±3.2±6.0) MeV/c2, widths of (55±17±53) MeV and (122.6±7.0±8.2) MeV, where the first errors are statistical and the second ones are systematic. The inclusion of a third Breit-Wigner amplitude is necessary to describe a structure around 4.79 GeV.
Using e+e− collision data corresponding to a total integrated luminosity of 12.9 fb−1 collected with the BESIII detector at the BEPCII collider, the exclusive Born cross sections and the effective form factors of the reaction e+e−→Ξ−Ξ¯+ are measured via the single baryon-tag method at 23 center-of-mass energies between 3.510 and 4.843 GeV. Evidence for the decay ψ(3770)→Ξ−Ξ¯+ is observed with a significance of 4.5σ by analyzing the measured cross sections together with earlier BESIII results. For the other charmonium(-like) states ψ(4040), ψ(4160), Y(4230), Y(4360), ψ(4415), and Y(4660), no significant signal of their decay to Ξ−Ξ¯+ is found. For these states, upper limits of the products of the branching fraction and the electronic partial width at the 90% confidence level are provided.
The process e+e−→D∗+sD∗−s is studied with a semi-inclusive method using data samples at center-of-mass energies from threshold to 4.95 GeV collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections of the process are measured for the first time with high precision in this energy region. Two resonance structures are observed in the energy-dependent cross sections around 4.2 and 4.4 GeV. By fitting the cross sections with a coherent sum of three Breit-Wigner amplitudes and one phase-space amplitude, the two significant structures are assigned masses of (4186.5±9.0±30) MeV/c2 and (4414.5±3.2±6.0) MeV/c2, widths of (55±17±53) MeV and (122.6±7.0±8.2) MeV, where the first errors are statistical and the second ones are systematic. The inclusion of a third Breit-Wigner amplitude is necessary to describe a structure around 4.79 GeV.
Determination of U-spin breaking parameters with an amplitude analysis of the decay D⁰ → K⁰Lπ⁺π⁻
(2022)
We present a study of the resonant structure of the decay D0→K0Lπ+π−, using quantum-correlated D0D¯0 data produced at s√=3.773 GeV. The data sample was collected by the BESIII experiment and corresponds to an integrated luminosity of 2.93 fb−1. This study is the first amplitude analysis of a decay mode involving a K0L, which also results in the first measurement of the complex U-spin breaking parameters (ρ^) related to various CP-eigenstate resonant modes through which the three-body decay proceeds. The moduli of the ρ^ parameters have central values in a wide range from 0.4 to 12.1, which indicates substantial U-spin symmetry breaking. We present the fractional resonant contributions and average strong-phase parameters over regions of phase space for both K0Sπ+π− and K0Lπ+π− modes. We also report the ratio of the branching fractions between K0Lπ+π− and K0Sπ+π− decay modes and the CP-even fraction of the K0Lπ+π− state calculated using the U-spin breaking parameters.