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With the data samples taken at center-of-mass energies from 2.00 to 3.08 GeV with the BESIII detector at the BEPCII collider, a partial wave analysis on the e+e−→π+π−π0 process is performed. The Born cross sections for e+e−→π+π−π0 and its intermediate processes e+e−→ρπ and ρ(1450)π are measured as functions of s√. The results for e+e−→π+π−π0 are consistent with previous results measured with the initial state radiation method within one standard deviation, and improve the uncertainty by a factor of ten. By fitting the line shapes of the Born cross sections for the e+e−→ρπ and ρ(1450)π, a structure with mass M=2119±11±15 MeV/c2 and width Γ=69±30±5MeV is observed with a significance of 5.9σ, where the first uncertainties are statistical and the second ones are systematic. This structure can be intepreteted as an excited ω state.
First study of antihyperon-nucleon scattering Λ¯p → Λ¯p and measurement of Λp → Λp cross section
(2024)
Using (10.087±0.044)×109 J/ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λp→Λp and Λ¯p→Λ¯p are studied, where the Λ/Λ¯ baryons are produced in the process J/ψ→ΛΛ¯ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in −0.9≤cosθΛ/Λ¯≤0.9 are measured to be σ(Λp→Λp)=(12.2±1.6stat±1.1sys) mb and σ(Λ¯p→Λ¯p)=(17.5±2.1stat±1.6sys) mb at the Λ/Λ¯ momentum of 1.074 GeV/c within a range of ±0.017 GeV/c, where the θΛ/Λ¯ are the scattering angles of the Λ/Λ¯ in the Λp/Λ¯p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λp→Λp, and a strong forward peak for Λ¯p→Λ¯p. We present an approach to extract the total elastic cross sections by extrapolation. The study of Λ¯p→Λ¯p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction.
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.
Using (2712.4 ± 14.3)×106 ψ(3686) events collected with the BESIII detector at BEPCII, a partial wave analysis of the decay ψ(3686)→ϕηη′ is performed with the covariant tensor approach. An axial-vector state with a mass near 2.3 GeV/c2 is observed for the first time. Its mass and width are measured to be 2316 ±9stat±30systMeV/c2 and 89 ±15stat±26systMeV, respectively. The product branching fractions of B(ψ(3686)→X(2300)η′)B(X(2300)→ϕη) and B(ψ(3686)→X(2300)η)B(X(2300)→ϕη′) are determined to be (4.8 ±1.3stat±0.7syst)×10−6 and (2.2 ±0.7stat±0.7syst)×10−6, respectively. The branching fraction B(ψ(3686)→ϕηη′) is measured for the first time to be (3.14±0.17stat±0.24syst)×10−5.
The first uncertainties are statistical and the second are systematic.
Based on (27.12±0.14)×108 ψ(2S) events collected with the BESIII detector, we search for the decay ηc(2S)→π+π−ηc with ηc→K0SK±π∓ and ηc→K+K−π0. 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 analysis of the process ψ(2S)→γηc(2S),ηc(2S)→π+π−K0SK±π∓ gives a clear ηc(2S) signal with a statistical significance of 10σ for the first time, %The product branching fraction B(ψ(2S)→γηc(2S))×B(ηc(2S)→π+π−K0SKπ) is measured to be (9.31±0.72±2.77)×10−6, and and the branching fraction B(ηc(2S)→π+π−K0SK±π∓) is determined to be (1.33±0.11±0.4±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)).
Using 24.1 fb−1 of e+e− collision data collected with the BESIII detector at the BEPCII collider, the Born cross sections and effective form factors of the e+e−→Σ+Σ¯− reaction are measured. The measurements are performed at center-of-mass energies ranging from 3.510 to 4.951 GeV. No significant evidence for the decay of the charmonium(-like) states, ψ(3770), ψ(4040), ψ(4160), Y(4230), Y(4360), ψ(4415), and Y(4660), into a Σ+Σ¯− final state is observed. Consequently, upper limits for the products of the branching fractions and the electronic partial widths at the 90% confidence level are reported for these decays.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, the cross section of the inclusive process e+e−→η+X, normalized by the total cross section of e+e−→hadrons, is measured at eight center-of-mass energy points from 2.0000 GeV to 3.6710 GeV. These are the first measurements with momentum dependence in this energy region. Our measurement shows a significant discrepancy from calculations with the existing fragmentation functions. To address this discrepancy, a new QCD analysis is performed at the next-to-next-to-leading order with hadron mass corrections and higher twist effects, which can explain both the established high-energy data and our measurements reasonably well.
Observation of χcJ → 3(K⁺K⁻)
(2023)
By analyzing (27.12±0.14)×108 ψ(3686) events collected with the BESIII detector operating at the BEPCII collider, the decay processes χcJ→3(K+K−) (J=0,1,2) are observed for the first time with statistical significances of 8.2σ, 8.1σ, and 12.4σ, respectively. The product branching fractions of ψ(3686)→γχcJ, χcJ→3(K+K−) are presented and the branching fractions of χcJ→3(K+K−) decays are determined to be Bχc0→3(K+K−)=(10.7±1.8±1.1)×10−6, Bχc1→3(K+K−)=(4.2±0.9±0.5)×10−6, and Bχc2→3(K+K−)=(7.2±1.1±0.8)×10−6, where the first uncertainties are statistical and the second are systematic.
Based on 4.5 fb−1 of e+e− collision data accumulated at center-of-mass energies between 4599.53 MeV and 4698.82 MeV with the BESIII detector, the decay Λ+c→nK0Sπ+π0 is observed for the first time with a significance of 9.2σ. The branching fraction is measured to be (0.85±0.13±0.03)%, where the first uncertainty is statistical and the second systematic, which differs from the theoretical prediction based on isospin by 4.4σ. This indicates that there may be resonant contributions or some unknown dynamics in this decay.