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Institute
Search for rare decays of Dₛ⁺ to final states π⁺e⁺e⁻, ρ⁺e⁺e⁻, π⁺π⁰e⁺e⁻, K⁺π⁰e⁺e⁻, and Kₛ⁰π⁺e⁺e⁻
(2024)
Using 7.33~fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies in the range of s√=4.128−4.226~GeV, we search for the rare decays D+s→h+(h0)e+e−, where h represents a kaon or pion. By requiring the e+e− invariant mass to be consistent with a ϕ(1020), 0.98<M(e+e−)<1.04 ~GeV/c2, the decay D+s→π+ϕ,ϕ→e+e− is observed with a statistical significance of 7.8σ, and evidence for the decay D+s→ρ+ϕ,ϕ→e+e− is found for the first time with a statistical significance of 4.4σ. The decay branching fractions are measured to be B(D+s→π+ϕ,ϕ→e+e−)=(1.17+0.23−0.21±0.03)×10−5, and B(D+s→ρ+ϕ,ϕ→e+e−)=(2.44+0.67−0.62±0.16)×10−5, where the first uncertainties are statistical and the second systematic. No significant signal for the three four-body decays of D+s→π+π0e+e−, D+s→K+π0e+e−, and D+s→K0Sπ+e+e− is observed. For D+s→π+π0e+e−, the ϕ mass region is vetoed to minimize the long-distance effects. The 90% confidence level upper limits set on the branching fractions of these decays are in the range of (7.0−8.1)×10−5.
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.
The Born cross sections and effective form factors of the process 𝑒+𝑒−→Λ¯Σ0+c.c. are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of (478.5±4.8) pb−1 collected with the BESIII detector. A nonzero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BABAR Collaboration. The Born cross-section line shape is described better by a shape considering the strong-interaction effects than by a pQCD motivated functional form.
The Born cross sections and effective form factors of the process e+e−→ΛΣ¯0+c.c. are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of (478.5±4.8) pb−1 collected with the BESIII detector. A non-zero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BaBar Collaboration. The Born cross-section lineshape is described better by a shape with a plateau near the threshold than by a pQCD motivated functional form.
The first observation of the decays J/ψ→p¯Σ+K0S and J/ψ→pΣ¯−K0S is reported using (10087±44)×106 J/ψ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of each channel are determined to be B(J/ψ→p¯Σ+K0S)=(1.361±0.006±0.025)×10−4 and B(J/ψ→pΣ¯−K0S)=(1.352±0.006±0.025)×10−4. The combined result is B(J/ψ→p¯Σ+K0S+c.c.)=(2.725±0.009±0.050)×10−4, where the first uncertainty is statistical and the second systematic. The results presented are in good agreement with the branching fractions of the isospin partner decay J/ψ→pK−Σ¯0+c.c..
Using 7.33~fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies in the range of s√=4.128−4.226~GeV, we search for the rare decays D+s→h+(h0)e+e−, where h represents a kaon or pion. By requiring the e+e− invariant mass to be consistent with a ϕ(1020), 0.98<M(e+e−)<1.04 ~GeV/c2, the decay D+s→π+ϕ,ϕ→e+e− is observed with a statistical significance of 7.8σ, and evidence for the decay D+s→ρ+ϕ,ϕ→e+e− is found for the first time with a statistical significance of 4.4σ. The decay branching fractions are measured to be B(D+s→π+ϕ,ϕ→e+e−)=(1.17+0.23−0.21±0.03)×10−5, and B(D+s→ρ+ϕ,ϕ→e+e−)=(2.44+0.67−0.62±0.16)×10−5, where the first uncertainties are statistical and the second systematic. No significant signal for the three four-body decays of D+s→π+π0e+e−, D+s→K+π0e+e−, and D+s→K0Sπ+e+e− is observed. For D+s→π+π0e+e−, the ϕ mass region is vetoed to minimize the long-distance effects. The 90% confidence level upper limits set on the branching fractions of these decays are in the range of (7.0−8.1)×10−5.
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 (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)).
A narrow structure in the pΛ¯ system near the mass threshold, named as X(2085), is observed in the process e+e−→pK−Λ¯ with a statistical significance greater than 20σ. Its spin and parity are determined for the first time to be JP=1+ in an amplitude analysis, with statistical significance greater than 5σ over other quantum numbers. The pole positions of X(2085) are measured to be Mpole=(2086±4±6)~MeV and Γpole=(56±5±16) MeV, where the first uncertainties are statistical and the second ones are systematic. The analysis is based on the study of the process e+e−→pK−Λ¯ and uses the data samples collected with the BESIII detector at the center-of-mass energies s√=4.008, 4.178, 4.226, 4.258, 4.416, and 4.682 GeV with a total integrated luminosity of 8.35 fb−1.
Using data samples collected with the BESIII detector at the BEPCII collider at center-of-mass energies ranging from 3.80 to 4.95 GeV, corresponding to an integrated luminosity of 20 fb−1, a measurement of Born cross sections for the e+e−→D0D¯0 and D+D− processes is presented with unprecedented precision. Many clear peaks in the line shape of e+e−→D0D¯0 and D+D− around the mass range of G(3900), ψ(4040), ψ(4160), Y(4260), and ψ(4415), etc., are foreseen. These results offer crucial experimental insights into the nature of hadron production in the open-charm region.
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.
Based on a data sample of (27.08±0.14)×108 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the M1 transition ψ(3686)→γηc(2S) with ηc(2S)→KK¯π is studied, where KK¯π is K+K−π0 or K0SK±π∓. The mass and width of the ηc(2S) are measured to be (3637.8±0.8(stat)±0.2(syst)) MeV/c2 and (10.5±1.7(stat)±3.5(syst)) MeV, respectively. The product branching fraction B(ψ(3686)→γηc(2S))×B(ηc(2S)→KK¯π) is determined to be (0.97±0.06(stat)±0.09(syst))×10−5. Using BR(ηc(2S)→KK¯π)=(1.86+0.68−0.49)%, we obtain the branching fraction of the radiative transition to be BR(ψ(3686)→γηc(2S))=(5.2±0.3(stat)±0.5(syst)+1.9−1.4(extr))×10−4, where the third uncertainty is due to the quoted BR(ηc(2S)→KK¯π).
The J/ψ→Ξ0Ξ¯0 process and subsequent decays are investigated using (10087±44)×106 J/ψ events collected at the BESIII experiment. The decay parameters of Ξ0 and Ξ¯0 are measured with greatly improved precision over previous measurements to be αΞ=−0.3750±0.0034±0.0016, α¯Ξ=0.3790±0.0034±0.0021, ϕΞ=0.0051±0.0096±0.0018~rad, ϕ¯Ξ=−0.0053±0.0097±0.0019~rad, where the first and the second uncertainties are statistical and systematic, respectively. From these measurements, precise CP symmetry tests in Ξ0 decay are performed, and AΞCP=(−5.4±6.5±3.1)×10−3 and ΔϕΞCP=(−0.1±6.9±0.9)×10−3~rad are consistent with CP conservation. The sequential decay also enables a separation of weak and strong phase differences, which are found for the first time to be ξP−ξS=(0.0±1.7±0.2)×10−2~rad and δP−δS=(−1.3±1.7±0.4)×10−2~rad, respectively. In addition, we measure the Λ decay parameters and test CP symmetry in Λ decays.
Using initial-state radiation events from a total integrated luminosity of 11.957 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at BEPCII, the cross section for the process 𝑒+𝑒−→Λ¯Λ is measured in 16 Λ¯Λ invariant mass intervals from the production threshold up to 3.00 GeV/𝑐2. The results are consistent with previous results from BABAR and BESIII, but with better precision and with narrower Λ¯Λ invariant mass intervals than BABAR.
Based on a sample of (448.1±2.9)×106 𝜓(3686) events collected with the BESIII detector at BEPCII, the decays of 𝜓(3686)→𝐾−Λ¯Ξ++c.c. with ¯Ξ+→¯Λ𝜋+, ¯Λ→¯𝑝𝜋+ are studied. We investigate the two excited resonances, Ξ(1690)− and Ξ(1820)−, which are each observed with large significance (≫10𝜎) in the 𝐾−Λ invariant mass distributions. A partial wave analysis is performed, and the spin-parities of Ξ(1690)− and Ξ(1820)− are measured to be 12− and 32−, respectively. The masses, widths, and product branching fractions of Ξ(1690)− and Ξ(1820)− are also measured.
Based on (2712.4±14.3)×106 events recorded at the 𝜓(3686) nominal mass collected with the BESIII detector operating at the BEPCII collider, the 𝜓(3686)→Σ+¯Σ−𝜔 and Σ+¯Σ−𝜙 decays are observed for the first time with statistical significances of 13.8𝜎 and 7.6𝜎, respectively. The corresponding branching fractions are measured to be ℬ(𝜓(3686)→Σ+¯Σ−𝜔)=(1.89±0.18±0.21)×10−5 and ℬ(𝜓(3686)→Σ+¯Σ−𝜙)=(2.96±0.54±0.41)×10−6, where the first uncertainties are statistical and the second systematic.
Using a sample of (27.12±0.14)×108 ψ(3686) events collected with the BESIII detector, the decay ψ(3686)→ΛΛ¯η′ with η′ subsequently decaying into γπ+π− and ηπ+π− is observed for the first time. The branching fraction of ψ(3686)→ΛΛ¯η′ is measured to be (7.34±0.94(stat.)±0.43(sys.))×10−6. No resonant structures are evident in the Λη′, Λ¯η′ and ΛΛ¯ mass spectra.