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By analyzing 4.48×108 ψ(3686) events collected with the BESIII detector, we observe the decays χcJ→nK0SΛ¯+c.c. (J=0, 1, 2) for the first time, via the radiative transition ψ(3686)→γχcJ. The branching fractions are determined to be (6.67±0.26stat±0.41syst)×10−4, (1.71±0.12stat±0.12syst)×10−4, and (3.66±0.17stat±0.23syst)×10−4 for J=0, 1, and 2, respectively.
By analyzing 4.48×108 ψ(3686) events collected with the BESIII detector, we observe the decays χcJ→nK0SΛ¯+c.c. (J=0, 1, 2) for the first time, via the radiative transition ψ(3686)→γχcJ. The branching fractions are determined to be (6.67±0.26stat±0.41syst)×10−4, (1.71±0.12stat±0.12syst)×10−4, and (3.66±0.17stat±0.23syst)×10−4 for J=0, 1, and 2, respectively.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data was collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− is observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− are observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− are observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
Based on a data sample of (1.0087±0.0044)×1010 𝐽/𝜓 events collected by the BESIII detector at the BEPCII accelerator, the absolute branching fraction (BF) of the decay 𝐽/𝜓→𝛾𝜂 is measured with high precision using events in which the radiative photon converts to 𝑒+𝑒−. Using the measured absolute BF of 𝐽/𝜓→𝛾𝜂, the absolute BFs of four dominant 𝜂 decay modes are measured for the first time. The results are ℬ(𝐽/𝜓→𝛾𝜂)=(1.067±0.005±0.023)×10−3, ℬ(𝜂→𝛾𝛾)=(39.86±0.04±0.99)%, ℬ(𝜂→𝜋0𝜋0𝜋0)=(31.96±0.07±0.84)%, ℬ(𝜂→𝜋+𝜋−𝜋0)=(23.04±0.03±0.54)%, and ℬ(𝜂→𝜋+𝜋−𝛾)=(4.38±0.02±0.10)%, where the first and second uncertainties are statistical and systematic, respectively. The results are consistent with the world average values within two standard deviations.
Based on a data sample of (1.0087+-0.0044)x10^10 Jpsi events collected by the BESIII detector at the BEPCII accelerator, the absolute branching fraction (BF) of the decay Jpsi->gamma eta is measured with high precision using events in which the radiative photon converts to e+e-. Using the measured absolute BF of Jpsi->gamma eta, the absolute BFs of four dominant eta decay modes are measured for the first time. The results are B(Jpsi->gamma eta) = (1.067+-0.005+-0.023)x10^-3, B(eta->gamma gamma) = (39.86+-0.04+-0.99)%, B(eta->pi0pi0pi0) = (31.96+-0.07+-0.84)%, B(eta->pi+pi-pi0) = (23.04+-0.03+-0.54)%, and B(eta->pi+pi-gamma) = (4.38+-0.02+-0.10)%, where the first and second uncertainties are statistical and systematic, respectively. The results are consistent with the world average values within two standard deviations.
Based on 4.481×108 ψ(3686) events collected with the BESIII detector at BEPCII, the branching fraction of the isospin violating decay ψ(3686)→Σ¯0Λ+c.c. is measured to be (1.60±0.31±0.13 ± 0.58)×10−6, where the first uncertainty is statistical, the second is systematic, and the third is the uncertainty arising from interference with the continuum. This result is significantly smaller than the measurement based on CLEO-c data sets. The decays χcJ→ΛΛ¯ are measured via ψ(3686)→γχcJ, and the branching fractions are determined to be B(χc0→ΛΛ¯)=(3.64±0.10±0.10±0.07)×10−4, B(χc1→ΛΛ¯)=(1.31±0.06±0.06±0.03)×10−4, B(χc2→ΛΛ¯)=(1.91±0.08±0.17±0.04)×10−4, where the third uncertainties are systematic due to the ψ(3686)→γχcJ branching fractions.
The decays D → K−π+π+π− and D → K−π+π 0 are studied in a sample of quantum-correlated DD¯ pairs produced through the process e+e− → ψ(3770) → DD¯, exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fb−1 . Here D indicates a quantum superposition of a D0 and a D¯ 0 meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle γ of the Unitarity Triangle in B− → DK− decays at the LHCb and Belle II experiments. The coherence factors are determined to be RK3π = 0.52+0.12−0.10 and RKππ0 = 0.78 ± 0.04, with values for the average strong-phase differences that are δ K3π D = (167+31−19)◦ and δKππ0D = (196+14−15◦ , where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the D → K−π+π+π− to yield results that will allow for a more sensitive measurement of γ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6◦.
Based on a sample of (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/ψ→γηη′ is performed. An isoscalar state with exotic quantum numbers JPC=1−+, denoted as η1(1855), has been observed for the first time with statistical significance larger than 19σ. Its mass and width are measured to be (1855±9+6−1)~MeV/c2 and (188±18+3−8)~MeV, respectively. The product branching fraction B(J/ψ→γη1(1855)→γηη′) is measured to be (2.70±0.41+0.16−0.35)×10−6. The first uncertainties are statistical and the second are systematic. In addition, an upper limit on the branching ratio B(f0(1710)→ηη′)/B(f0(1710)→ππ) is determined to be 1.61×10−3 at 90\% confidence level, which lends support to the hypothesis that the f0(1710) has a large glueball component.