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The process 𝑒+𝑒−→𝜙𝜂′ has been studied for the first time in detail using data sample collected with the BESIII detector at the BEPCII collider at center of mass energies from 2.05 to 3.08 GeV. A resonance with quantum numbers 𝐽𝑃𝐶=1−− is observed with mass 𝑀=(2177.5±4.8(stat)±19.5(syst))MeV/𝑐2 and width Γ=(149.0±15.6(stat)±8.9(syst)) MeV with a statistical significance larger than 10𝜎, including systematic uncertainties. If the observed structure is identified with the 𝜙(2170), then the ratio of partial width between the 𝜙𝜂′ by BESIII and 𝜙𝜂 by BABAR is (ℬ𝑅𝜙𝜂Γ𝑅𝑒𝑒)/(ℬ𝑅𝜙𝜂′Γ𝑅𝑒𝑒)=0.23±0.10(stat)±0.18(syst), which is smaller than the prediction of the 𝑠¯𝑠𝑔 hybrid models by several orders of magnitude.
Using a low background data sample of 9.7×105 𝐽/𝜓→𝛾𝜂′, 𝜂′→𝛾𝜋+𝜋− events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of 𝜂′→𝛾𝜋+𝜋− are studied with both model-dependent and model-independent approaches. The contributions of 𝜔 and the 𝜌(770)−𝜔 interference are observed for the first time in the decays 𝜂′→𝛾𝜋+𝜋− in both approaches. Additionally, a contribution from the box anomaly or the 𝜌(1450) resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.
Using a sample of (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector, we perform the first partial wave analysis of ψ(3686)→K+K−η. In addition to the well established states, ϕ(1020), ϕ(1680), and K∗3(1780), contributions from X(1750), ρ(2150), ρ3(2250), and K∗2(1980) are also observed. The X(1750) state is determined to be a 1−− resonance. The simultaneous observation of the ϕ(1680) and X(1750) indicates that the X(1750), with previous observations in photoproduction, is distinct from the ϕ(1680). The masses, widths, branching fractions of ψ(3686)→K+K−η and the intermediate resonances are also measured.
Using a sample of 1.31×109 J/ψ events collected by the BESIII detector at BEPCII during 2009 and 2012, we study the J/ψ→ωη′π+π− hadronic process. For the first time, we measure the branching ratio B(J/ψ→ωη′π+π−)=(1.12±0.02±0.13)×10−3. We search for the X(1835) state in the η′π+π− invariant mass spectra. No evidence is found and we estimate the upper limit on the branching fraction at 90% confidence level to be B(J/ψ→ωX(1835),X(1835)→η′π+π−)<6.2×10−5.
Several intermediate states of the reaction channels 𝑒+𝑒−→𝜋+𝜋−𝐷0¯𝐷0 and 𝑒+𝑒−→𝜋+𝜋−𝐷+𝐷− are studied using the data samples collected with the BESIII detector at center-of-mass energies above 4.08 GeV. For the first time in this final state, a 𝜓(3770) signal is seen in the 𝐷¯𝐷 invariant mass spectrum, with a statistical significance of 5.2𝜎 at √𝑠=4.42 GeV. There is also evidence for this resonance at √𝑠=4.26 and 4.36 GeV with statistical significance of 3.2𝜎 and 3.3𝜎, respectively. In addition, the Born cross section of 𝑒+𝑒−→𝜋+𝜋−𝜓(3770) is measured. The proposed heavy-quark-spin-symmetry partner of the 𝑋(3872), the state 𝑋2(4013), is also searched for in the 𝐷¯𝐷 invariant mass spectra. No obvious signal is found. The upper limit of the Born cross section of the process 𝑒+𝑒−→𝜌0𝑋2(4013) combined with the branching fraction is measured. Also, the processes 𝑒+𝑒−→𝐷1(2420)¯𝐷+c.c. are investigated. The neutral mode with 𝐷1(2420)0→𝐷0𝜋+𝜋− is reported with statistical significance of 7.4𝜎 at √𝑠=4.42 GeV for the first time, and evidence with statistical significance of 3.2𝜎 and 3.3𝜎 at √𝑠=4.36 and 4.60 GeV is seen, respectively. No evident signal for the process 𝑒+𝑒−→𝐷1(2420)0¯𝐷0+c.c.,𝐷1(2420)0→𝐷*+𝜋− is reported. Evidence for 𝑒+𝑒−→𝐷1(2420)+𝐷−+c.c.,𝐷1(2420)+→𝐷+𝜋+𝜋− is reported with statistical significance of 3.1𝜎 and 3.0𝜎 at √𝑠=4.36 and 4.42 GeV, respectively.
The SU(3)-flavor violating decay J/ψ→Ξ(1530)−Ξ¯++c.c. is studied using (1310.6±7.0)×106 J/ψ events collected with the BESIII detector at BEPCII and the branching fraction is measured to be B(J/ψ→Ξ(1530)−Ξ¯++c.c.) = (3.17±0.02stat.±0.08syst.)×10−4. This is consistent with previous measurements with an improved precision. The angular parameter for this decay is measured for the first time and is found to be α=−0.21±0.04stat.±0.06syst.. In addition, we report evidence for the radiative decay Ξ(1530)−→γΞ− with a significance of 3.9σ, including the systematic uncertainties. The 90\% confidence level upper limit on the branching fraction is determined to be B(Ξ(1530)−→γΞ−)≤3.7\%.
Using a total of 11.0 fb−1 of e+e− collision data with center-of-mass energies between 4.009 GeV and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process e+e−→Ξ−Ξ¯+ by means of a single baryon-tag method. After performing a fit to the dressed cross section of e+e−→Ξ−Ξ¯+, no significant ψ(4230) or ψ(4260) resonance is observed in the Ξ−Ξ¯+ final states, and upper limits at the 90\% confidence level on ΓeeB for the processes ψ(4230)/ψ(4260)→Ξ−Ξ¯+ are determined. In addition, an excited Ξ baryon at 1820 MeV/c2 is observed with a statistical significance of 6.2 ∼ 6.5σ by including the systematic uncertainty, and the mass and width are measured to be M=(1825.5±4.7±4.7)~MeV/c2 and Γ=(17.0±15.0±7.9)~MeV, which confirms the existence of the JP=32− state Ξ(1820).
Using 448.1 × 106 ψ(3686) events collected with the BESIII detector at BEPCII, we employ a single-baryon tagging technique to make the first observation of ψ(3686) → Ξ(1530)−Ξ¯(1530)+ and Ξ(1530)−Ξ¯+ decays with a statistical significance of more than 10σ and 5.0σ, respectively. The branching fractions are measured to be B[ψ(3686)→Ξ(1530)−Ξ¯(1530)+] = (11.45 ± 0.40 ± 0.59) × 10−5 and B[ψ(3686)→Ξ(1530)−Ξ¯+] = (0.70 ± 0.11 ± 0.04) × 10−5. The angular distribution parameter for ψ(3686) → Ξ(1530)−Ξ¯(1530)+ is determined to be α = 0.40 ± 0.24 ± 0.06, which agrees with the theoretical predictions within 1σ. The first uncertainties are statistical, and the second systematic.
The Born cross section for the process e+e−→pp¯ is measured using the initial state radiation technique with an undetected photon. This analysis is based on datasets corresponding to an integrated luminosity of 7.5 fb−1, collected with the BESIII detector at the BEPCII collider at center of mass energies between 3.773 and 4.600 GeV. The Born cross section for the process e+e−→pp¯ and the proton effective form factor are determined in the pp¯ invariant mass range between 2.0 and 3.8 GeV/c2 divided into 30 intervals. The proton form factor ratio (|GE|/|GM|) is measured in 3 intervals of the pp¯ invariant mass between 2.0 and 3.0 GeV/c2.
Using a 2.93 fb−1 data sample of electron-positron collisions taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, which corresponds to (8296±31±64)×103D+D− pairs, we search for the baryon and lepton number violating decays D+→Λ¯(Σ¯0)e+ and D+→Λ(Σ0)e+. No obvious signals are found with the current statistics and upper limits on the branching fractions of these four decays are set at the level of 10−6 at 90% confidence level.