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Search for the reaction channel e⁺e⁻ → ηcηπ⁺π⁻ at center-of-mass energies from 4.23 to 4.60 GeV
(2021)
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process 𝑒+𝑒−→𝜂𝑐𝜂𝜋+𝜋−. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The 𝜂𝑐 meson is reconstructed in 16 exclusive decay modes. No signal is observed in the 𝜂𝑐 mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.
We measure the Born cross sections of the process 𝑒+𝑒−→𝐾+𝐾−𝐾+𝐾− at center-of-mass (c.m.) energies, √𝑠, between 2.100 and 3.080 GeV. The data were collected using the BESIII detector at the BEPCII collider. An enhancement at √𝑠=2.232 GeV is observed, very close to the 𝑒+𝑒−→Λ¯Λ production threshold. A similar enhancement at the same c.m. energy is observed in the 𝑒+𝑒−→𝜙𝐾+𝐾− cross section. The energy dependence of the 𝐾+𝐾−𝐾+𝐾− and 𝜙𝐾+𝐾− cross sections differs significantly from that of 𝑒+𝑒−→𝜙𝜋+𝜋−.
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.
A partial-wave analysis of the decay 𝐽/𝜓→𝐾+𝐾−𝜋0 has been made using (223.7±1.4)×106 𝐽/𝜓 events collected with the BESIII detector in 2009. The analysis, which is performed within the isobar-model approach, reveals contributions from 𝐾*2(1430)±, 𝐾*2(1980)± and 𝐾*4(2045)± decaying to 𝐾±𝜋0. The two latter states are observed in 𝐽/𝜓 decays for the first time. Two resonance signals decaying to 𝐾+𝐾− are also observed. These contributions cannot be reliably identified and their possible interpretations are discussed. The measured branching fraction 𝐵(𝐽/𝜓→𝐾+𝐾−𝜋0) of (2.88±0.01±0.12)×10−3 is more precise than previous results. Branching fractions for the reported contributions are presented as well. The results of the partial-wave analysis differ significantly from those previously obtained by BESII and BABAR.
We study the hadronic decays of Λ+c to the final states Σ+η and Σ+η′, using an e+e− annihilation data sample of 567 pb−1 taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays Λ+c→Σ+η and Σ+η′ with statistical significance of 2.5σ and 3.2σ, respectively. Normalizing to the reference decays Λ+c→Σ+π0 and Σ+ω, we obtain the ratios of the branching fractions B(Λ+c→Σ+η)B(Λ+c→Σ+π0) and B(Λ+c→Σ+η′)B(Λ+c→Σ+ω) to be 0.35±0.16±0.03 and 0.86±0.34±0.07, respectively. The upper limits at the 90\% confidence level are set to be B(Λ+c→Σ+η)B(Λ+c→Σ+π0)<0.58 and B(Λ+c→Σ+η′)B(Λ+c→Σ+ω)<1.2. Using BESIII measurements of the branching fractions of the reference decays, we determine B(Λ+c→Σ+η)=(0.41±0.19±0.05)% (<0.68%) and B(Λ+c→Σ+η′)=(1.34±0.53±0.21)% (<1.9%). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of Λ+c→Σ+η is consistent with the previous measurement, and the branching fraction of Λ+c→Σ+η′ is measured for the first time.
We report on new measurements of Cabibbo-suppressed semileptonic D+s decays using 3.19 fb−1 of e+e− annihilation data sample collected at a center-of-mass energy of 4.178~GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions B(D+s→K0e+νe)=(3.25±0.38(stat.)±0.16(syst.))×10−3 and B(D+s→K∗0e+νe)=(2.37±0.26(stat.)±0.20(syst.))×10−3 which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For D+s→K0e+νe, we obtain f+(0)=0.720±0.084(stat.)±0.013(syst.), and for D+s→K∗0e+νe, we find form-factor ratios rV=V(0)/A1(0)=1.67±0.34(stat.)±0.16(syst.) and r2=A2(0)/A1(0)=0.77±0.28(stat.)±0.07(syst.).
We study the electromagnetic Dalitz decay 𝐽/𝜓→𝑒+𝑒−𝜂 and search for dielectron decays of a dark gauge boson (𝛾′) in 𝐽/𝜓→𝛾′𝜂 with the two 𝜂 decay modes 𝜂→𝛾𝛾 and 𝜂→𝜋+𝜋−𝜋0 using (1310.6±7.0)×106 𝐽/𝜓 events collected with the BESIII detector. The branching fraction of 𝐽/𝜓→𝑒+𝑒−𝜂 is measured to be (1.43±0.04(stat)±0.06(syst))×10−5, with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be Λ=2.84±0.11(stat)±0.08(syst) GeV/𝑐2. We find no evidence of 𝛾′ production and set 90% confidence level upper limits on the product branching fraction ℬ(𝐽/𝜓→𝛾′𝜂)×ℬ(𝛾′→𝑒+𝑒−) as well as the kinetic mixing strength between the standard model photon and 𝛾′ in the mass range of 0.01≤𝑚𝛾′≤2.4 GeV/𝑐2.
An amplitude analysis of the 𝐾𝑆𝐾𝑆 system produced in radiative 𝐽/𝜓 decays is performed using the (1310.6±7.0)×106 𝐽/𝜓 decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parametrizing the 𝐾𝑆𝐾𝑆 invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the 𝐾𝑆𝐾𝑆 system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the 𝑓0(1710), 𝑓0(2200), and 𝑓′2(1525). The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative 𝐽/𝜓 decays to 𝐾𝑆𝐾𝑆 is measured to be (8.1±0.4)×10−4, where the uncertainty is systematic and the statistical uncertainty is negligible.
he process e+e−→pK0Sn¯K−+c.c. and its intermediate processes are studied for the first time, using data samples collected with the BESIII detector at BEPCII at center-of-mass energies of 3.773, 4.008, 4.226, 4.258, 4.358, 4.416, and 4.600 GeV, with a total integrated luminosity of 7.4 fb−1. The Born cross section of e+e−→pK0Sn¯K−+c.c. is measured at each center-of-mass energy, but no significant resonant structure in the measured cross-section line shape between 3.773 and 4.600 GeV is observed. No evident structure is detected in the pK−, nK0S, pK0S, nK+, pn¯, or K0SK− invariant mass distributions except for Λ(1520). The Born cross sections of e+e−→Λ(1520)n¯K0S+c.c. and e+e−→Λ(1520)p¯K++c.c. are measured, and the 90\% confidence level upper limits on the Born cross sections of e+e−→Λ(1520)Λ¯(1520) are determined at the seven center-of-mass energies.