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By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the 𝐷+→𝜂𝜇+𝜈𝜇 decay to be ℬ𝐷+→𝜂𝜇+𝜈𝜇=(10.4±1.0stat±0.5syst)×10−4. Using the world averaged value of ℬ𝐷+→𝜂𝑒+𝜈𝑒, the ratio of the two branching fractions is determined to be ℬ𝐷+→𝜂𝜇+𝜈𝜇/ℬ𝐷+→𝜂𝑒+𝜈𝑒=0.91±0.13(stat+syst), which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor 𝑓𝜂+(0) and the 𝑐→𝑑 Cabibbo-Kobayashi-Maskawa matrix element |𝑉𝑐𝑑| to be 𝑓𝜂+(0)|𝑉𝑐𝑑|=0.087±0.008stat±0.002syst. Taking the input of |𝑉𝑐𝑑| from the global fit in the standard model, we determine 𝑓𝜂+(0)=0.39±0.04stat±0.01syst. On the other hand, using the value of 𝑓𝜂+(0) calculated in theory, we find |𝑉𝑐𝑑| = 0.242±0.022stat±0.006syst±0.033theory.
Using a dedicated data sample taken in 2018 on the J/ψ peak, we perform a detailed study of the trigger efficiencies of the BESIII detector. The efficiencies are determined from three representative physics processes, namely Bhabha scattering, dimuon production and generic hadronic events with charged particles. The combined efficiency of all active triggers approaches 100% in most cases, with uncertainties small enough not to affect most physics analyses.
Using 𝑒+𝑒−→Λ+𝑐¯Λ−𝑐 production from a 567 pb−1 data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried out simultaneously on the four decay modes of Λ+𝑐→𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0, and Σ0𝜋+. For the first time, the Λ+𝑐 transverse polarization is studied in unpolarized 𝑒+𝑒− collisions, where a nonzero effect is observed with a statistical significance of 2.1𝜎. The decay asymmetry parameters of the Λ+𝑐 weak hadronic decays into 𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0 and Σ0𝜋+ are measured to be 0.18±0.43(stat)±0.14(syst), −0.80±0.11(stat)±0.02(syst), −0.57±0.10(stat)±0.07(syst), and −0.73±0.17(stat)±0.07(syst), respectively. In comparison with previous results, the measurements for the Λ𝜋+ and Σ+𝜋0 modes are consistent but with improved precision, while the parameters for the 𝑝𝐾0𝑆 and Σ0𝜋+ modes are measured for the first time.
Using (10.087±0.044)×109 𝐽/𝜓 events collected by the Beijing Spectrum III (BESIII) detector at the Beijing Electron Positron Collider II (BEPCII) collider, we search for the hyperon semileptonic decay Ξ−→Ξ0𝑒−¯𝜈𝑒. No significant signal is observed and the upper limit on the branching fraction ℬ(Ξ−→Ξ0𝑒−¯𝜈𝑒) is set to be 2.59×10−4 at 90% confidence level. This result is one order of magnitude more strict than the previous best limit.
By analyzing an electron-positron collision data sample corresponding to an integrated luminosity of 2.93 fb−1 taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, we obtain for the first time the absolute branching fractions for seven 𝐷0 and 𝐷+ hadronic decay modes and search for the hadronic decay 𝐷0→𝐾0𝑆𝐾0𝑆𝜋0 with much improved sensitivity. The results are ℬ(𝐷0→𝐾0𝑆𝜋0𝜋0𝜋0)=(7.64±0.30±0.29)×10−3, (𝐷0→𝐾−𝜋+𝜋0𝜋0𝜋0)=9.54±0.30±0.31)×10−3, ℬ(𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0𝜋0)=(12.66±0.45±0.43)×10−3, ℬ(𝐷+→𝐾0𝑆𝜋+𝜋0𝜋0)=(29.04±0.62±0.87)×10−3, ℬ(𝐷+→𝐾0𝑆𝜋+𝜋+𝜋−𝜋0)=(15.28±0.57±0.60)×10−3, ℬ(𝐷+→𝐾0𝑆𝜋+𝜋0𝜋0𝜋0)=(5.54±0.44±0.32)×10−3, ℬ(𝐷+→𝐾−𝜋+𝜋+𝜋0𝜋0)=(4.95±0.26±0.19)×10−3, and ℬ(𝐷0→𝐾0𝑆𝐾0𝑆𝜋0)<1.45×10−4 at the 90% confidence level. Here, the first uncertainties are statistical, and the second ones are systematic. The newly studied decays greatly enrich the knowledge of the 𝐷→¯𝐾𝜋𝜋𝜋 and 𝐷→¯𝐾𝜋𝜋𝜋𝜋 hadronic decays and open a bridge to access more two-body hadronic 𝐷 decays containing scalar, vector, axial, and tensor mesons in the charm sector.
he Born cross sections for the process 𝑒+𝑒−→𝜂′𝜋+𝜋− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3𝜎 and a mass and width of 𝑀=(2111±43±25) MeV/𝑐2 and Γ=(135±34±30) MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in 𝑒+𝑒−→𝜂′𝜋+𝜋− and BESIII in 𝑒+𝑒−→𝜔𝜋0 within two standard deviations.
Using inclusive decays of the J/ψ, a precise determination of the number of J/ψ events collected with the BESIII detector is performed. For the two data sets taken in 2009 and 2012, the numbers of J/ψ events are recalculated to be (224.0±1.3)×106 and (1088.5±4.4)×106 respectively, which are in good agreement with the previous measurements. For the J/ψ sample taken in 2017--2019, the number of events is determined to be (8774.0±39.4)×106. The total number of J/ψ events collected with the BESIII detector is determined to be (10087±44)×106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
Using inclusive decays of the J/ψ, a precise determination of the number of J/ψ events collected with the BESIII detector is performed. For the two data sets taken in 2009 and 2012, the numbers of J/ψ events are recalculated to be (224.0±1.3)×106 and (1088.5±4.4)×106 respectively, which are in good agreement with the previous measurements. For the J/ψ sample taken in 2017--2019, the number of events is determined to be (8774.0±39.4)×106. The total number of J/ψ events collected with the BESIII detector is determined to be (10087±44)×106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
We present the first experimental search for the rare charm decay D0→π0ν¯ν. It is based on an e+e− collision sample consisting of 10.6×10^6 pairs of D0¯D0 mesons collected by the BESIII detector at √s=3.773 GeV, corresponding to an integrated luminosity of 2.93 fb^−1. A data-driven method is used to ensure the reliability of the background modeling. No significant D0→π0ν¯ν signal is observed in data and an upper limit of the branching fraction is set to be 2.1×10^-4 at the 90% confidence level. This is the first experimental constraint on charmed-hadron decays into dineutrino final states.
The Born cross sections and effective form factors for process 𝑒+𝑒−→Ξ−¯Ξ+ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb−1 𝑒+𝑒− collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross section of 𝑒+𝑒−→Ξ−¯Ξ+, no significant threshold effect is observed.