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The decays of χc2→K+K−π0, KSK±π∓ and π+π−π0 are studied with the ψ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of χc2→K∗K¯¯¯¯¯, χc2→a±2(1320)π∓/a02(1320)π0 and χc2→ρ(770)±π∓ are measured. Here K∗K¯¯¯¯¯ denotes both K∗±K∓ and K∗0K¯¯¯¯¯0+c.c., and K∗ denotes the resonances K∗(892), K∗2(1430) and K∗3(1780). The observations indicate a strong violation of the helicity selection rule in χc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of χc2→K∗(892)K¯¯¯¯¯ are more than 20 times larger than that of χc2→ρ(770)±π∓, which implies the effects are largely due to U-spin symmetry breaking, rather than just isospin symmetry breaking in charmonium decays.
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.
The decays of χc2→K+K−π0, KSK±π∓ and π+π−π0 are studied with the ψ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of χc2→K∗K¯¯¯¯¯, χc2→a±2(1320)π∓/a02(1320)π0 and χc2→ρ(770)±π∓ are measured. Here K∗K¯¯¯¯¯ denotes both K∗±K∓ and K∗0K¯¯¯¯¯0+c.c., and K∗ denotes the resonances K∗(892), K∗2(1430) and K∗3(1780). The observations indicate a strong violation of the helicity selection rule in χc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of χc2→K∗(892)K¯¯¯¯¯ are more than 10 times larger than the upper limit of χc2→ρ(770)±π∓, which is so far the first direct observation of a significant U-spin symmetry breaking effect in charmonium decays.
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.
Using 2.93fb−1 of e+e− collision data collected at a center-of-mass energy of 3.773\,GeV with the BESIII detector, we present a measurement of the branching fraction of the doubly Cabibbo-suppressed (DCS) decay D0→K+π−π0 and a search for the DCS decay D0→K+π−π0π0. The branching fraction of D0→K+π−π0 is determined to be [3.13+0.60−0.56(stat)±0.09(syst)]×10−4. No signal is observed for D0→K+π−π0π0 and an upper limit of 3.6×10−4 is set on the branching fraction at the 90\% C.L. We combine these results with the world-average branching fractions of their counterpart Cabibbo-favored decays to determine the ratios of the doubly Cabibbo-suppressed over the Cabibbo-favored branching fractions, B(D0→K+π−π0)/B(D0→K−π+π0)=(0.22±0.04)%~and B(D0→K+π−π0π0)/B(D0→K−π+π0π0)<0.40% at the 90\% C.L., which correspond to (0.75±0.14)tan4θC~and 1.37×tan4θC, respectively, where θC is the Cabibbo angle.
Based on an 𝑒+𝑒− collision data sample corresponding to an integrated luminosity of 2.93 fb−1 collected with the BESIII detector at √𝑠=3.773 GeV, the first amplitude analysis of the singly Cabibbo-suppressed decay 𝐷+→𝐾+𝐾0𝑆𝜋0 is performed. From the amplitude analysis, the 𝐾*(892)+𝐾0𝑆 component is found to be dominant with a fraction of (57.1±2.6±4.2)%, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction ℬ(𝐷+→𝐾+𝐾0𝑆𝜋0) measured by BESIII, we obtain ℬ(𝐷+→𝐾*(892)+𝐾0𝑆)=(8.69±0.40±0.64±0.51)×10−3, where the third uncertainty is due to the branching fraction ℬ(𝐷+→𝐾+𝐾0𝑆𝜋0). The precision of this result is significantly improved compared to the previous measurement. This result also differs from most of theoretical predictions by about 4𝜎, which may help to improve the understanding of the dynamics behind.
The Born cross sections and effective form factors for process 𝑒+𝑒−→Ξ−¯Ξ+ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb−1 𝑒+𝑒− collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross section of 𝑒+𝑒−→Ξ−¯Ξ+, no significant threshold effect is observed.
We present the first experimental search for the rare charm decay D0→π0ν¯ν. It is based on an e+e− collision sample consisting of 10.6×10^6 pairs of D0¯D0 mesons collected by the BESIII detector at √s=3.773 GeV, corresponding to an integrated luminosity of 2.93 fb^−1. A data-driven method is used to ensure the reliability of the background modeling. No significant D0→π0ν¯ν signal is observed in data and an upper limit of the branching fraction is set to be 2.1×10^-4 at the 90% confidence level. This is the first experimental constraint on charmed-hadron decays into dineutrino final states.
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.