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Institute
Using a sample of 4.48×108 ψ(3686) events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons π0, η, η′, η(1405), η(1475), η(1760), and X(1835) in J/ψ radiative decays using ψ(3686)→π+π−J/ψ events. The π0, η and η′ mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be B(J/ψ→γπ0→3γ)=(3.57±0.12±0.16)×10−5, B(J/ψ→γη→3γ)=(4.42±0.04±0.18)×10−4, and B(J/ψ→γη′→3γ)=(1.26±0.02±0.05)×10−4, where the first errors are statistical and the second systematic. No clear signal for η(1405), η(1475), η(1760) or X(1835) is observed in the two-photon mass spectra, and upper limits at the 90% confidence level on the product branching fractions are obtained.
Using a data sample of 448.1×106 𝜓(3686) events collected with the BESIII detector operating at the BEPCII, we perform search for the hadronic transition ℎ𝑐→𝜋+𝜋−𝐽/𝜓 via 𝜓(3686)→𝜋0ℎ𝑐. No signals of the transition are observed, and the upper limit on the product branching fraction ℬ(𝜓(3686)→𝜋0ℎ𝑐)ℬ(ℎ𝑐→𝜋+𝜋−𝐽/𝜓) at the 90% confidence level (C.L.) is determined to be 2.0×10−6. This is the most stringent upper limit to date.
We search for the semi-leptonic decays Λ + c → Λπ+π−e+νe and Λ + c → pK0 Sπ−e+νe in a sample of 4.5 fb−1 of e+e− annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Λ+c → Λπ+π−e+νe ) < 3.9 × 10−4 and B(Λ + c → pK0Sπ−e+νe ) < 3.3 × 10−4 at the 90% confidence level, respectively.
We search for an axion-like particle (ALP) a through the process ψ(3686)→π+π−J/ψ, J/ψ→γa, a→γγ in a data sample of (2.71±0.01)×109 ψ(3686) events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ψ→γa and the ALP-photon coupling constant gaγγ are set at 95% confidence level in the mass range of 0.165≤ma≤2.84GeV/c2. The limits on B(J/ψ→γa) range from 8.3×10−8 to 1.8×10−6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165≤ma≤1.468GeV/c2.
We report a search for a dark photon using 14.9~fb−1 of e+e− annihilation data taken at center-of-mass energies from 4.13 to 4.60~GeV with the BESIII detector operated at the BEPCII storage ring. The dark photon is assumed to be produced in the radiative annihilation process of e+e− and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9~GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90% confidence level on the coupling strength parameter ϵ for a dark photon coupling with an ordinary photon vary between 1.6×10−3 and 5.7×10−3.
Using 16 energy points of e+e− annihilation data collected in the vicinity of the J/ψ resonance with the BESIII detector and with a total integrated luminosity of around 100 pb−1, we study the relative phase between the strong and electromagnetic amplitudes of J/ψ decays. The relative phase between J/ψ electromagnetic decay and the continuum process (e+e− annihilation without the J/ψ resonance) is confirmed to be zero by studying the cross section lineshape of μ+μ− production. The relative phase between J/ψ strong and electromagnetic decays is then measured to be (84.9 ± 3.6)◦ or (−84.7 ± 3.1)◦ for the 2(π+π−)π0 final state by investigating the interference pattern between the J/ψ decay and the continuum process. This is the first measurement of the relative phase between J/ψ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state ηπ+π− with η → π+π−π0, which provides additional information about the phase between the J/ψ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/ψ → 2(π+π−)π0 is measured to be (4.73 ± 0.44)% or (4.85 ± 0.45)%, and the branching fraction of J/ψ → ηπ+π− is measured to be (3.78 ± 0.68) × 10−4. Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.
Measurement of the e+e−→π+π− cross section between 600 and 900 MeV using initial state radiation
(2016)
We extract the e+e− →π+π− cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb−1 taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor |Fπ|2 as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (g−2)μ. We find this value to be aππ,LO μ (600–900 MeV) = (368.2 ±2.5stat±3.3sys) ·10−10, which is between the corresponding values using the BaBar or KLOE data.
We report the first measurement of the absolute branching fraction for Λ+c→Λμ+νμ. This measurement is based on a sample of e+e− annihilation data at a center-of-mass energy of s√=4.6 GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb−1. The branching fraction is determined to be B(Λ+c→Λμ+νμ)=(3.49±0.46(stat)±0.27(syst))%. In addition, we calculate the ratio B(Λ+c→Λμ+νμ)/B(Λ+c→Λe+νe) to be 0.96±0.16(stat)±0.04(syst).
We study the decays of J/ψ and ψ(3686) to the final states Σ(1385)0Σ¯(1385)0 and Ξ0Ξ¯0 based on a single baryon tag method using data samples of (1310.6±7.0)×106 J/ψ and (447.9±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider. The decays to Σ(1385)0Σ¯(1385)0 are observed for the first time. The measured branching fractions of J/ψ and ψ(3686)→Ξ0Ξ¯0 are in good agreement with, and much more precise, than the previously published results. The angular parameters for these decays are also measured for the first time. The measured angular decay parameter for J/ψ→Σ(1385)0Σ¯(1385)0, α=−0.64±0.03±0.10, is found to be negative, different to the other decay processes in this measurement. In addition, the "12\% rule" and isospin symmetry in the J/ψ and ψ(3686)→ΞΞ¯ and Σ(1385)Σ¯(1385) systems are tested.
By analyzing 2.93 fb−1 of data taken at the ψ(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ → K0S K0S K +, D+ → K0S K0Sπ+, D0 → K0S K0S and D0 → K0S K0S K0S . They are determined to be B(D+ → K0S K0S K +) = (2.54 ± 0.05stat. ± 0.12sys.) × 10−3, B(D+ → K0S K0Sπ+) = (2.70 ± 0.05stat. ± 0.12sys.) × 10−3, B(D0 → K0S K0S ) = (1.67 ± 0.11stat. ± 0.11sys.) × 10−4 and B(D0 → K0S K0S K0S ) = (7.21 ± 0.33stat. ± 0.44sys.) × 10−4, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.