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Based on (27.12±0.14)×108 𝜓(2𝑆) events collected by the BESIII detector, we search for the decay 𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂𝑐 via 𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆). No significant signal is observed, and the upper limit on the product branching fraction ℬ(𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆))×ℬ(𝜂𝑐(2𝑆)→𝜋+𝜋−𝜂𝑐) is determined to be 2.21×10−5 at the 90% confidence level. In addition, the 𝜂𝑐(2𝑆)→𝜋+𝜋−𝐾0𝑆𝐾±𝜋∓ decay is studied via 𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆) and is observed with a statistical significance of 10𝜎 for the first time. The branching fraction of 𝜂𝑐(2𝑆)→𝜋+𝜋−𝐾0𝑆𝐾±𝜋∓ is determined to be (1.33±0.11±0.40±0.95)×10−2, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the quoted ℬ(𝜓(2𝑆)→𝛾𝜂𝑐(2𝑆)).
Based on (2712.4±14.1)×106 𝜓(3686) events collected with the BESIII detector, we study the decays ℎ𝑐→3(𝜋+𝜋−)𝜋0, ℎ𝑐→2(𝜋+𝜋−)𝜔, ℎ𝑐→2(𝜋+𝜋−)𝜋0𝜂, ℎ𝑐→2(𝜋+𝜋−)𝜂, and ℎ𝑐→𝑝¯𝑝 via 𝜓(3686)→𝜋0ℎ𝑐. The decay channel ℎ𝑐→3(𝜋+𝜋−)𝜋0 is observed for the first time, and its branching fraction is determined to be (9.28±1.14±0.77)×10−3, where the first uncertainty is statistical and the second is systematic. In addition, first evidence is found for the modes ℎ𝑐→2(𝜋+𝜋−)𝜋0𝜂 and ℎ𝑐→2(𝜋+𝜋−)𝜔 with significances of 4.8𝜎 and 4.7𝜎, and their branching fractions are determined to be (7.55±1.51±0.77)×10−3 and (4.00±0.86±0.35)×10−3, respectively. No significant signals of ℎ𝑐→2(𝜋+𝜋−)𝜂 and ℎ𝑐→𝑝¯𝑝 are observed, and the upper limits of the branching fractions of these decays are determined to be <6.19×10−4 and <4.40×10−5 at the 90% confidence level, respectively.
The processes hc→γP(P=η′, η, π0) are studied with a sample of (27.12±0.14)×108 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The decay hc→γη is observed for the first time with the significance of 9.0σ, and the branching fraction is determined to be (3.77±0.55±0.13±0.26)×10−4, while B(hc→γη′) is measured to be (1.40±0.11±0.04±0.10)×10−3, where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ(3686)→π0hc. The combination of these results allows for a precise determination of Rhc=B(hc→γη)B(hc→γη′), which is calculated to be (27.0±4.4±1.0)%. The results are valuable for gaining a deeper understanding of η−η′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay hc→γπ0, and an upper limit is placed on its branching fraction of B(hc→γπ0)<5.0×10−5, at the 90% confidence level.
The J/ψ,ψ(3686)→Σ0Σ¯0 processes and subsequent decays are studied using the world's largest J/ψ and ψ(3686) data samples collected with the BESIII detector. The strong-CP symmetry is tested in the decays of the Σ0 hyperons for the first time by measuring the decay parameters, αΣ0=−0.0017±0.0021±0.0018 and α¯Σ0=0.0021±0.0020±0.0022. The weak-CP test is performed in the subsequent decays of their daughter particles Λ and Λ¯. Also for the first time, the transverse polarizations of the Σ0 hyperons in J/ψ and ψ(3686) decays are observed with opposite directions, and the ratios between the S-wave and D-wave contributions of the J/ψ,ψ(3686)→Σ0Σ¯0 decays are obtained. These results are crucial to understand the decay dynamics of the charmonium states and the production mechanism of the Σ0−Σ¯0 pairs.
Based on (2712.4±14.3)×106 ψ(3686) events, we investigate four hadronic decay modes of the P-wave charmonium spin-singlet state hc(1P1)→h+h−π0/η (h=π or K) via the process ψ(3686)→π0hc at BESIII. The hc→π+π−π0 decay is observed with a significance of 9.6σ after taking into account systematic uncertainties. Evidences for hc→K+K−π0 and hc→K+K−η are found with significances of 3.5σ and 3.3σ, respectively, after considering the systematic uncertainties. The branching fractions of these decays are measured to be B(hc→π+π−π0)=(1.36±0.16±0.14)×10−3, B(hc→K+K−π0)=(3.26±0.84±0.36)×10−4, and B(hc→K+K−η)=(3.13±1.08±0.38)×10−4, where the first uncertainties are statistical and the second are systematic. No significant signal of hc→π+π−η is found, and the upper limit of its decay branching fraction is determined to be B(hc→π+π−η)<4.0×10−4 at 90% confidence level.
The Ξ0 asymmetry parameters are measured using entangled quantum Ξ0 − Ξ¯ 0 pairs from a sample of ð448.1 2.9Þ × 106 ψð3686Þ events collected with the BESIII detector at BEPCII. The relative phase between the transition amplitudes of the Ξ0Ξ¯ 0 helicity states is measured to be ΔΦ ¼ −0.050 0.150 0.020 rad, which implies that there is no obvious polarization at the current level of statistics. The decay parameters of the Ξ0 hyperon ðαΞ0 ; αΞ¯ 0 ; ϕΞ0 ; ϕΞ¯ 0 Þ and the angular distribution parameter ½αψð3686Þ and ΔΦ are measured simultaneously for the first time. In addition, the CP asymmetry observables are determined to be AΞ0 CP ¼ ðαΞ0 þ αΞ¯ 0 Þ=ðαΞ0 − αΞ¯ 0 Þ ¼ −0.007 0.082 0.025 and ΔϕΞ0 CP ¼ ðϕΞ0 þ ϕΞ¯ 0 Þ=2 ¼ −0.079 0.082 0.010 rad, which are consistent with CP conservation.
Using an 𝑒+𝑒− collision data sample of (27.08±0.14)×108 𝜓(3686) events collected by the BESIII detector, we report the first observation of 𝜒𝑐𝐽→Ω−¯Ω+ (𝐽=0, 1, 2) decays with significances of 5.6𝜎, 6.4𝜎, and 18𝜎, respectively, where the 𝜒𝑐𝐽 mesons are produced in the radiative 𝜓(3686) decays. The branching fractions are determined to be ℬ(𝜒𝑐0→Ω−¯Ω+) = (3.51±0.54±0.29)×10−5, ℬ(𝜒𝑐1→Ω−¯Ω+)=(1.49±0.23±0.10)×10−5, and ℬ(𝜒𝑐2→Ω−¯Ω+)=(4.52±0.24±0.18)×10−5, where the first and second uncertainties are statistical and systematic, respectively.
Based on 4.5 fb−1 data taken at seven center-of-mass energies ranging from 4.600 to 4.699 GeV with the BESIII detector at the BEPCII collider, we measure the branching fractions of Λ + c → Σ + + hadrons relative to Λ + c → Σ +π +π −. Combining with the world average branching fraction of Λ + c → Σ +π +π −, their branching fractions are measured to be (0.377 ± 0.042 ± 0.020 ± 0.021)% for Λ + c → Σ +K+K−, (0.200 ± 0.023 ± 0.011 ± 0.011)% for Λ + c → Σ+K+π−, (0.414 ± 0.080 ± 0.030 ± 0.023)% for Λ + c → Σ +φ and (0.197 ± 0.036 ± 0.009 ± 0.011)% for Λ + c → Σ +K+K−(non-φ). In all the above results, the first uncertainties are statistical, the second are systematic and the third are from external input of the branching fraction of Λ + c → Σ +π +π −. Since no signal for Λ + c → Σ +K+π−π 0 is observed, the upper limit of its branching fraction is determined to be 0.13% at the 90% confidence level.
Using data corresponding to an integrated luminosity of 651 pb−1 accumulated at 22 center-of-mass energies from 2.00 to 3.08 GeV by the BESIII experiment, the process 𝑒+𝑒−→𝜙𝜋+𝜋− is studied. The cross sections for 𝑒+𝑒−→𝜙𝜋+𝜋− are consistent with previous results, but with improved precision. To measure the mass and width of the structure observed in the cross section line shape, a combine fit is performed after enhancing the contribution from 𝜙𝑓0(980). The fit reveals a structure with the mass of 𝑀=2178±20±5 MeV/𝑐2 and the width of Γ=140±36±16 MeV, where the first uncertainties are statistical and the second ones are systematic.
Based on (2712.4±14.3)×106 𝑒+𝑒−→𝜓(3686) events collected with the BESIII detector operating at the BEPCII Collider, we report the first evidence of 𝜒𝑐0→Λ¯Λ𝜙 decays and the first observation of 𝜒𝑐1,2→Λ¯Λ𝜙 decays, with significances of 4.1𝜎, 11.3𝜎 and 13.0𝜎, respectively. The decay branching fractions of 𝜒𝑐0,1,2→Λ¯Λ𝜙 are measured to be (2.99±1.24±0.19)×10−5, (6.01±0.90±0.40)×10−5, and (7.13±0.81±0.36)×10−5, where the first uncertainties are statistical and the second systematic. No obvious enhancement near the Λ¯Λ production threshold or excited Λ state is found in the Λ𝜙 (or ¯Λ𝜙) system.