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Using a data sample of 448.1×106 𝜓(3686) events collected at √𝑠=3.686 GeV with the BESIII detector at the Beijing Electron-Positron Collider II, we search for the rare decay 𝐽/𝜓→𝜙𝑒+𝑒− via 𝜓(3686)→𝜋+𝜋−𝐽/𝜓. No signal events are observed and the upper limit on the branching fraction is set to be ℬ(𝐽/𝜓→𝜙𝑒+𝑒−)<1.2×10−7 at the 90% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.
Using 2.93 fb−1 of e+e− collision data collected with the BESIII detector at a center-of-mass energy of 3.773 GeV, we measure the absolute branching fractions of the decays D0→K−e+νe and D+→K¯0e+νe to be (3.567±0.031stat±0.025syst)% and (8.68±0.14stat±0.16syst)%, respectively. Starting with the process e+e−→DD¯, a new reconstruction method is employed to select events that contain candidates for both D→K¯e+νe and D¯→Ke−ν¯e decays. The branching fractions reported in this work are consistent within uncertainties with previous BESIII measurements that selected events containing D→K¯e+νe and hadronic D¯ decays. Combining our results with the lifetimes of the D0 and D+ mesons and the previous BESIII measurements leads to a ratio of the two decay partial widths of Γ¯D0→K−e+νeΓ¯D+→K¯0e+νe=1.039±0.021. This ratio supports isospin symmetry in the D0→K−e+νe and D+→K¯0e+νe decays within 1.9σ.
Using a data sample of 4.481×108 𝜓(3686) events collected with the BESIII detector, we report the first observation of the four-lepton-decays 𝐽/𝜓→𝑒+𝑒−𝑒+𝑒− and 𝐽/𝜓→𝑒+𝑒−𝜇+𝜇− utilizing the process 𝜓(3686)→𝜋+𝜋−𝐽/𝜓. The branching fractions are determined to be [5.48±0.31(stat)±0.45(syst)]×10−5 and [3.53±0.22(stat)±0.13(syst)]×10−5, respectively. The results are consistent with theoretical predictions. No significant signal is observed for 𝐽/𝜓→𝜇+𝜇−𝜇+𝜇−, and an upper limit on the branching fraction is set at 1.6×10−6 at the 90% confidence level. A 𝐶𝑃 asymmetry observable is constructed for the first two channels, which is measured to be (−0.012±0.054±0.010) and (0.062±0.059±0.006), respectively. No evidence for 𝐶𝑃 violation is observed in this process.
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.
Using a sample of about 1010 𝐽/𝜓 events collected at a center-of-mass energy √𝑠=3.097 GeV with the BESIII detector, the electromagnetic Dalitz decays 𝐽/𝜓→𝑒+𝑒−𝜋+𝜋−𝜂′, with 𝜂′→𝛾𝜋+𝜋− and 𝜂′→𝜋+𝜋−𝜂, have been studied. The decay 𝐽/𝜓→𝑒+𝑒−𝑋(1835) is observed with a significance of 15𝜎, and also an 𝑒+𝑒− invariant-mass dependent transition form factor of 𝐽/𝜓→𝑒+𝑒−𝑋(1835) is presented for the first time. The intermediate states 𝑋(2120) and 𝑋(2370) are also observed in the 𝜋+𝜋−𝜂′ invariant-mass spectrum with significances of 5.3𝜎 and 7.3𝜎. The corresponding product branching fractions for 𝐽/𝜓→𝑒+𝑒−𝑋, 𝑋→𝜋+𝜋−𝜂′ [𝑋=𝑋(1835), 𝑋(2120), and 𝑋(2370)] are reported.
Using 2.93 fb−1 of 𝑒+𝑒− collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, the first observation of the doubly Cabibbo-suppressed decay 𝐷+→𝐾+𝜋+𝜋−𝜋0 is reported. After removing decays that contain narrow intermediate resonances, including 𝐷+→𝐾+𝜂, 𝐷+→𝐾+𝜔, and 𝐷+→𝐾+𝜙, the branching fraction of the decay 𝐷+→𝐾+𝜋+𝜋−𝜋0 is measured to be (1.13±0.08stat±0.03syst)×10−3. The ratio of branching fractions of 𝐷+→𝐾+𝜋+𝜋−𝜋0 over 𝐷+→𝐾−𝜋+𝜋+𝜋0 is found to be (1.81±0.15)%, which corresponds to (6.28±0.52)tan4𝜃𝐶, where 𝜃𝐶 is the Cabibbo mixing angle. This ratio is significantly larger than the corresponding ratios for other doubly Cabibbo-suppressed decays. The asymmetry of the branching fractions of charge-conjugated decays 𝐷±→𝐾±𝜋±𝜋∓𝜋0 is also determined, and no evidence for 𝐶𝑃 violation is found. In addition, the first evidence for the 𝐷+→𝐾+𝜔 decay, with a statistical significance of 3.3𝜎, is presented and the branching fraction is measured to be ℬ(𝐷+→𝐾+𝜔) = (5.7+2.5−2.1stat±0.2syst)×10−5.
The Born cross sections for the process e+e−→η′π+π− at different center-of-mass energies between 2.00 and 3.08~GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3σ and a mass and width of M=(2108±46±25)~MeV/c2 and Γ=(138±36±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+e−→η′π+π− and BESIII in e+e−→ωπ0 within two standard deviations.
The Born cross sections for the process e+e−→η′π+π− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3σ and a mass and width of M=(2111±43±25)~MeV/c2 and Γ=(135±34±30)~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in e+e−→η′π+π− and BESIII in e+e−→ωπ0 within two standard deviations.
Using a sample of 1.31×109 𝐽/𝜓 events collected with the BESIII detector, we perform a study of 𝐽/𝜓→𝛾𝜂𝜂𝜂′ to search for the 𝑋(2370) and 𝜂𝑐 in the 𝜂𝜂𝜂′ invariant mass distribution. No significant signal for the 𝑋(2370) is observed, and we set an upper limit for the product branching fraction of ℬ(𝐽/𝜓→𝛾𝑋(2370)·ℬ(𝑋(2370)→𝜂𝜂𝜂′)<9.2×10−6 at the 90% confidence level. A clear 𝜂𝑐 signal is observed for the first time, yielding a product branching fraction of ℬ(𝐽/𝜓→𝛾𝜂𝑐)·ℬ(𝜂𝑐→𝜂𝜂𝜂′)=(4.86±0.62(stat)±0.45(sys))×10−5.
We report an amplitude analysis and branching fraction measurement of 𝐷+
𝑠→𝐾+𝐾−𝜋+ decay using a data sample of 3.19 fb−1 recorded with BESIII detector at a center-of-mass energy of 4.178 GeV. We perform a model-independent partial wave analysis in the low 𝐾+𝐾− mass region to determine the 𝐾+𝐾− S-wave line shape, followed by an amplitude analysis of our very pure high-statistics sample. With the detection efficiency based on the amplitude analysis results, the absolute branching fraction is measured to be ℬ(𝐷+𝑠→𝐾+𝐾−𝜋+)=(5.47±0.08stat±0.13sys)%.