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The radiative hyperon decay Λ→𝑛𝛾 is studied using (10087±44)×106 𝐽/𝜓 events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay Λ→𝑛𝛾 is determined to be (0.832±0.038stat±0.054syst)×10−3, which is a factor of 2.1 lower and 5.6 standard deviations different than the previous measurement. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry 𝛼𝛾 is reported with a value of −0.16±0.10stat±0.05syst.
A search for the charged lepton flavor violating decay 𝐽/𝜓→𝑒±𝜏∓ with 𝜏∓→𝜋∓𝜋0𝜈𝜏 is performed with about 10×109 𝐽/𝜓 events collected with the BESIII detector at the BEPCII. No significant signal is observed, and an upper limit is set on the branching fraction ℬ(𝐽/𝜓→𝑒±𝜏∓)<7.5×10−8 at the 90% confidence level. This improves the previously published limit by two orders of magnitude.
By analyzing an e+e− annihilation 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 the branching fraction of the D0→ρ−μ+νμ decay for the first time. We obtain BD0→ρ−μ+νμ=(1.35±0.09stat±0.09syst)×10−3. Using the world average of BD0→ρ−e+νe, we find a branching fraction ratio of BD0→ρ−μ+νμ/BD0→ρ−e+νe=0.90±0.11, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. Combining the world average of BD+→ρ0μ+νμ and the lifetimes of D0(+), we obtain a partial decay width ratio of ΓD0→ρ−μ+νμ/(2ΓD+→ρ0μ+νμ)=0.71±0.14, which is consistent with the isospin symmetry expectation of one within 2.1σ. For the reported values of BD0→ρ−μ+νμ/BD0→ρ−e+νe and ΓD0→ρ−μ+νμ/2ΓD+→ρ0μ+νμ, the uncertainty is the quadratic sum of the statistical and systematic uncertainties.
Improved measurement of the branching fractions of the inclusive decays D⁺ → Kₛ⁰X and D⁰ → Kₛ⁰X
(2023)
By analyzing 2.93 fb−1 of 𝑒+𝑒− collision data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, the branching fractions of the inclusive decays 𝐷+→𝐾0 𝑆𝑋 and 𝐷0→𝐾0 𝑆𝑋 are measured to be (33.11±0.13±0.36)% and (20.75±0.12±0.20)%, respectively, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world averages of previous measurements, but with much improved precision.
Ten hadronic final states of the ℎ𝑐 decays are investigated via the process 𝜓(3686)→𝜋0ℎ𝑐, using a data sample of (448.1±2.9)×106 𝜓(3686) events collected with the BESIII detector. The decay channel ℎ𝑐→𝐾+𝐾−𝜋+𝜋−𝜋0 is observed for the first time and has a measured significance of 6.0𝜎. The corresponding branching fraction is determined to be ℬ(ℎ𝑐→𝐾+𝐾−𝜋+𝜋−𝜋0)=(3.3±0.6±0.6)×10−3 (where the uncertainties are statistical and systematic, respectively). Evidence for the decays ℎ𝑐→𝜋+𝜋−𝜋0𝜂 and ℎ𝑐→𝐾0𝑆𝐾±𝜋∓𝜋+𝜋− is found with a significance of 3.6𝜎 and 3.8𝜎, respectively. The corresponding branching fractions (and upper limits) are obtained to be ℬ(ℎ𝑐→𝜋+𝜋−𝜋0𝜂)=(7.2±1.8±1.3)×10−3 (<1.8×10−2) and ℬ(ℎ𝑐→𝐾0𝑆𝐾±𝜋∓𝜋+𝜋−)=(2.8±0.9±0.5)×10−3 (<4.7×10−3). Upper limits on the branching fractions for the final states ℎ𝑐→𝐾+𝐾−𝜋0, 𝐾+𝐾−𝜂, 𝐾+𝐾−𝜋+𝜋−𝜂, 2(𝐾+𝐾−)𝜋0, 𝐾+𝐾−𝜋0𝜂, 𝐾0𝑆𝐾±𝜋∓, and 𝑝¯𝑝𝜋0𝜋0 are determined at a confidence level of 90%.
The decays J/ψ→ηΣ+Σ¯− and ψ(3686)→ηΣ+Σ¯− are observed for the first time, using (10087±44)×106 J/ψ and (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider. We determine the branching fractions of these two decays to be B(J/ψ→ηΣ+Σ¯−)=(6.34±0.21±0.37)×10−5 and B(ψ(3686)→ηΣ+Σ¯−)=(9.59±2.37±0.61)×10−6, where the first uncertainties are statistical and the second are systematic. The ratio of these two branching fractions is determined to be B(ψ(3686)→ηΣ+Σ¯−)B(J/ψ→ηΣ+Σ¯−)=(15.1±3.8)%, which is in agreement with the "12\% rule."
We study the processes e+e−→K0SD+sD∗− and e+e−→K0SD∗+sD−, as well as their charge conjugated processes, at five center-of-mass energies between 4.628~GeV and 4.699~GeV, using data samples corresponding to an integrated luminosity of 3.8 fb−1 collected by the BESIII detector at the BEPCII storage ring. Based on a partial reconstruction technique, we find evidence of a structure near the thresholds for D+sD∗− and D∗+sD− production in the K0S recoil-mass spectrum, which we refer to as the Zcs(3985)0. Fitting with a Breit-Wigner line shape, we find the mass of the structure to be (3992.2±1.7±1.6) MeV/c2 and the width to be (7.7+4.1−3.8±4.3) MeV, where the first uncertainties are statistical and the second are systematic. The significance of the Zcs(3985)0 signal is found to be 4.6σ including both the statistical and systematic uncertainty. We report the Born cross section multiplied by the branching fraction at different energy points. The mass of the Zcs(3985)0 is close to that of the Zcs(3985)+. Assuming SU(3) symmetry, the cross section of the neutral channel is consistent with that of the charged one. Hence, we conclude that the Zcs(3985)0 is the isospin partner of the Zcs(3985)+.
Using 10.1 × 109 J/ψ events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy √s = 3.097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/ψ → D−e+νe + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction B(J/ψ → D−e +νe + c.c.) < 7.1 × 10−8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.
During the 2016-17 and 2018-19 running periods, the BESIII experiment collected 7.5~fb−1 of e+e− collision data at center-of-mass energies ranging from 4.13 to 4.44~GeV. These data samples are primarily used for the study of excited charmonium and charmoniumlike states. By analyzing the di-muon process e+e−→(γISR/FSR)μ+μ−, we measure the center-of-mass energies of the data samples with a precision of 0.6 MeV. Through a run-by-run study, we find that the center-of-mass energies were stable throughout most of the data-taking period.
During the 2016-17 and 2018-19 running periods, the BESIII experiment collected 7.5~fb−1 of e+e− collision data at center-of-mass energies ranging from 4.13 to 4.44 GeV. These data samples are primarily used for the study of excited charmonium and charmoniumlike states. By analyzing the di-muon process e+e−→(γISR/FSR)μ+μ−, we measure the center-of-mass energies of the data samples with a precision of 0.6 MeV. Through a run-by-run study, we find that the center-of-mass energies were stable throughout most of the data-taking period.