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Measurement of e⁺e⁻ → π⁺π⁻D⁺D⁻ cross sections at center-of-mass energies from 4.190 to 4.946 GeV
(2022)
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the e+e−→π+π−D+D− process at center-of-mass energies from 4.190 to 4.946 GeV with a partial reconstruction method. Two resonance structures are seen and the resonance parameters are determined from a fit to the cross section line shape. The first resonance we observe has a mass of (4373.1 ± 4.0 ± 2.2) MeV/c2 and a width of (146.5 ± 7.4 ± 1.3) MeV, in agreement with those of the Y(4390) state; the other resonance has a mass of (4706 ± 11 ± 4) MeV/c2, a width of (45 ± 28 ± 9) MeV, and a statistical significance of 4.1 standard deviations (σ). This is the first evidence for a vector state at this mass value. The spin-3 D-wave charmonium state X(3842) is searched for through the e+e−→π+π−X(3842)→π+π−D+D− process, and evidence with a significance of 4.2σ is found in the data samples with center-of-mass energies from 4.600 to 4.700 GeV.
The decays J/ψ→ηΣ+Σ¯− and ψ(3686)→ηΣ+Σ¯− are observed for the first time, using (10087±44)×106 J/ψ and (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider. We determine the branching fractions of these two decays to be B(J/ψ→ηΣ+Σ¯−)=(6.34±0.21±0.37)×10−5 and B(ψ(3686)→ηΣ+Σ¯−)=(9.59±2.37±0.61)×10−6, where the first uncertainties are statistical and the second are systematic. The ratio of these two branching fractions is determined to be B(ψ(3686)→ηΣ+Σ¯−)B(J/ψ→ηΣ+Σ¯−)=(15.1±3.8)%, which is in agreement with the "12\% rule."
Quantum-correlated 𝐷¯𝐷 pairs collected by the BESIII experiment at the 𝜓(3770) resonance corresponding to an integrated luminosity of 2.93 fb−1 are used to study the 𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0 decay mode. The 𝐶𝑃-even fraction of 𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0 decays is determined to be 0.235±0.010±0.002, where the first uncertainty is statistical and the second is systematic.
he decay D→K−π+ is studied in a sample of quantum-correlated DD¯ pairs, based on a data set corresponding to an integrated luminosity of 2.93\,fb−1 collected at the ψ(3770) resonance by the BESIII experiment. The asymmetry between CP-odd and CP-even eigenstate decays into K−π+ is determined to be AKπ=0.132±0.011±0.007, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a K0L meson. The branching fractions of the K0L modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D→π+π−π0 and the ensemble of CP-odd eigenstate tags, the observable Aπππ0Kπ is measured to be 0.130±0.012±0.008. The two asymmetries are sensitive to rKπDcosδKπD, where rKπD and δKπD are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D→K−π+ tagged by D→K0S,Lπ+π− are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both rKπDcosδKπD and rKπDsinδKπD. A fit to AKπ, Aπππ0Kπ and the phase-space distribution of the D→K0S,Lπ+π− tags yields δKπD=(187.5+8.9−9.7+5.4−6.4) degrees, where external constraints are applied for rKπD and other relevant parameters. This is the most precise measurement of δKπD in quantum-correlated DD¯ decays.
The decay D→K−π+ is studied in a sample of quantum-correlated DD¯ pairs, based on a data set corresponding to an integrated luminosity of 2.93\,fb−1 collected at the ψ(3770) resonance by the BESIII experiment. The asymmetry between CP-odd and CP-even eigenstate decays into K−π+ is determined to be AKπ=0.132±0.011±0.007, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a K0L meson. The branching fractions of the K0L modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D→π+π−π0 and the ensemble of CP-odd eigenstate tags, the observable Aπππ0Kπ is measured to be 0.130±0.012±0.008. The two asymmetries are sensitive to rKπDcosδKπD, where rKπD and δKπD are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D→K−π+ tagged by D→K0S,Lπ+π− are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both rKπDcosδKπD and rKπDsinδKπD. A fit to AKπ, Aπππ0Kπ and the phase-space distribution of the D→K0S,Lπ+π− tags yields δKπD=(187.6+8.9−9.7+5.4−6.4) degrees, where external constraints are applied for rKπD and other relevant parameters. This is the most precise measurement of δKπD in quantum-correlated DD¯ decays.
Based on a sample of 448.1×106 ψ(3686) events collected with the BESIII detector, a study of ψ(3686)→ΛΛ¯π0 and ψ(3686)→ΛΛ¯η is performed. Evidence of the isospin-violating decay ψ(3686)→ΛΛ¯π0 is found for the first time with a statistical significance of 3.7σ, the branching fraction B(ψ(3686)→ΛΛ¯π0) is measured to be (1.42±0.39±0.59)×10−6, and its corresponding upper limit is determined to be 2.47×10−6 at 90\% confidence level. A partial wave analysis of ψ(3686)→ΛΛ¯η shows that the peak around Λη invariant mass threshold favors a Λ∗ resonance with mass and width in agreement with the Λ(1670). The branching fraction of the ψ(3686)→ΛΛ¯η is measured to be (2.34±0.18±0.52)×10−5. The first uncertainties are statistical and the second are systematic.
Based on e+e− collision data corresponding to an integrated luminosity of 4.5 fb−1 collected at the center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII, the absolute branching fraction of the inclusive decay Λ+c→n+X, where X refers to any possible final state particles, is measured. The absolute branching fraction is determined to be B(Λ+c→n+X)=(32.4±0.7±1.5)%, where the first uncertainty is statistical and the second systematic. Assuming CP symmetry, the measurement indicates that about one-fourth of Λ+c (Λ¯−c) decay modes with a neutron (an anti-neutron) in the final state have not been observed.
Based on e+e− collision data corresponding to an integrated luminosity of 4.5 fb−1 collected at the center-of-mass energies between 4.600 and 4.699 Gev with the BESIII detector at BEPCII, the absolute branching fraction of the inclusive decay Λ¯−c→n¯+X, where X refers to any possible final state particles, is measured. The absolute branching fraction is determined to be B(Λ¯−c→n¯+X)=(33.5±0.7±1.2)%, where the first uncertainty is statistical and the second systematic. Neglecting the effect of CP violation, the measurement indicates that about one-fourth of Λ+c decay modes with a neutron in the final state have not been observed.
First study of reaction Ξ⁰n → Ξ⁻ p using Ξ⁰-nucleus scattering at an electron-positron collider
(2023)
Using ð1.0087 0.0044Þ × 1010 J=ψ events collected with the BESIII detector at the BEPCII storage ring, the process Ξ0n → Ξ−p is studied, where the Ξ0 baryon is produced in the process J=ψ → Ξ0Ξ¯ 0 and the neutron is a component of the 9 Be, 12C, and 197Au nuclei in the beam pipe. A clear signal is observed with a statistical significance of 7.1σ. The cross section of the reaction Ξ0 þ 9 Be → Ξ− þ p þ 8 Be is determined to be σðΞ0 þ 9 Be → Ξ− þ p þ 8 BeÞ¼ð22.1 5.3stat 4.5sysÞ mb at the Ξ0 momentum of 0.818 GeV=c, where the first uncertainty is statistical and the second is systematic. No significant H-dibaryon signal is observed in the Ξ−p final state. This is the first study of hyperon-nucleon interactions in electron-positron collisions and opens up a new direction for such research.
The Cabbibo-favored decay Λ+c→Ξ0K+π0 is studied for the first time using 6.1 fb−1 of e+e− collision data at center-of-mass energies between 4.600 and 4.840 GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay Λ+c→Ξ0K+π0 is measured to be (7.79±1.46±0.71)×10−3, where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay Λ+c→Ξ(1530)0K+ is (5.99±1.04±0.29)×10−3, which is consistent with the previous result of (5.02±0.99±0.31)×10−3. In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay Λ+c→nK+π0 is 7.1×10−4 at the 90% confidence level. The upper limits on the branching fractions of Λ+c→Σ0K+π0 and ΛK+π0 are also determined to be 1.8×10−3 and 2.0×10−3, respectively.
