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The quantum entangled J/ψ→Σ+Σ¯− pairs from (1.0087±0.0044)×1010 J/ψ events taken by the BESIII detector are used to study the non-leptonic two-body weak decays Σ+→nπ+ and Σ¯−→n¯π−. The CP-odd weak decay parameters of the decays Σ+→nπ+ (α+) and Σ¯−→n¯π− (α¯−) are determined to be −0.0565±0.0047stat±0.0022syst and 0.0481±0.0031stat±0.0019syst, respectively. The decay parameter α¯− is measured for the first time, and the accuracy of α+ is improved by a factor of four compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of ACP=(α++α¯−)/(α+−α¯−) = −0.080±0.052stat±0.028syst. Assuming CP conservation, the average decay parameter is determined as ⟨α+⟩=(α+−α¯−)/2 = −0.0506±0.0026stat±0.0019syst, while the ratios α+/α0 and α¯−/α¯0 are −0.0490±0.0032stat±0.0021syst and −0.0571±0.0053stat±0.0032syst, where α0 and α¯0 are the decay parameters of the decays Σ+→pπ0 and Σ¯−→p¯π0, respectively.
The quantum entangled J=ψ → ΣþΣ¯ − pairs from ð1.0087 0.0044Þ × 1010 J=ψ events taken by the BESIII detector are used to study the nonleptonic two-body weak decays Σþ → nπþ and Σ¯ − → n¯π−. The CP-odd weak decay parameters of the decays Σþ → nπþ (αþ) and Σ¯ − → n¯π− (α¯−) are determined to be 0.0481 0.0031stat 0.0019syst and −0.0565 0.0047stat 0.0022syst, respectively. The decay parameter α¯− is measured for the first time, and the accuracy of αþ is improved by a factor of 4 compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of ACP ¼ ðαþ þ α¯−Þ=ðαþ − α¯−Þ ¼ −0.080 0.052stat 0.028syst. Assuming CP conservation, the average decay parameter is determined as hαþi¼ðαþ − α¯−Þ=2 ¼ −0.0506 0.0026stat 0.0019syst, while the ratios αþ=α0 and α¯−=α¯ 0 are −0.0490 0.0032stat 0.0021syst and −0.0571 0.0053stat 0.0032syst, where α0 and α¯ 0 are the decay parameters of the decays Σþ → pπ0 and Σ¯ − → p¯ π0, respectively.
Using 𝑒+𝑒− collision data with an integrated luminosity of 7.33 fb−1 collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector operating at the BEPCII collider, the branching fraction of the leptonic decay 𝐷+ 𝑠→𝜇+𝜈𝜇 is measured to be (0.5294±0.0108stat±0.0085syst)%. Based on this, the product of the 𝐷+ 𝑠 decay constant 𝑓𝐷+ 𝑠 and the magnitude of the 𝑐→𝑠 quark mixing matrix element |𝑉𝑐𝑠| is determined to be 𝑓𝐷+ 𝑠|𝑉𝑐𝑠| = 241.8±2.5stat±2.2syst MeV. Using the value of |𝑉𝑐𝑠| given by the global standard model fit, 𝑓𝐷+ 𝑠 is found to be 248.4±2.5stat±2.2syst MeV. Alternatively, using the value of 𝑓𝐷+ 𝑠 from a recent lattice quantum chromodynamics calculation, |𝑉𝑐𝑠| is determined to be 0.968±0.010stat±0.009syst.
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.
We report the measurement of the cross sections for e+e−→hadrons at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe a new resonance R(3810) in the cross sections for the first time, and observe the R(3760) resonance with high significance in the cross sections. The R(3810) has a mass of (3804.5±0.9±0.9) ~MeV/c2, a total width of (5.4±3.5±3.2)~MeV, and an electronic partial width of (19.4±7.4±12.1)~eV. Its significance is 7.7σ. The R(3810) could be interpreted as a hadro-charmonium resonance predicted by Quantum Chromodynamics (QCD). In addition, we measure the mass (3751.9±3.8±2.8) ~MeV/c2, the total width (32.8±5.8±8.7)~MeV, and the electronic partial width (184±75±86)~eV with improved precision for the R(3760). Furthermore, for the R(3780) we measure the mass (3778.7±0.5±0.3) ~MeV/c2 and total width (20.3±0.8±1.7)~MeV with improved precision, and the electronic partial width (265±69±83)~eV. The R(3780) can be interpreted as the 13D1 state of charmonium. Its mass and total width differ significantly from the corresponding fitted values given by the Particle Data Group in 2022 by 7.1 and 3.2 times the uncertainties for ψ(3770), respectively. ψ(3770) has been interpreted as the 13D1 state for 45 years.
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.
Using (1.0087±0.0044)×1010 𝐽/𝜓 events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays Ξ0→𝐾−𝑒+ with Δ(𝐵−𝐿)=0 and Ξ0→𝐾+𝑒− with |Δ(𝐵−𝐿)|=2, where 𝐵 (𝐿) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to ℬ(Ξ0→𝐾−𝑒+)<3.6×10−6 and ℬ(Ξ0→𝐾+𝑒−)<1.9×10−6 at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.
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.
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.
Precision measurements of the semileptonic decays 𝐷+𝑠→𝜂𝑒+𝜈𝑒 and 𝐷+𝑠→𝜂′𝑒+𝜈𝑒 are performed with 7.33 fb−1 of 𝑒+𝑒− collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector. The branching fractions obtained are ℬ(𝐷+𝑠→𝜂𝑒+𝜈𝑒) = (2.255±0.039stat±0.051syst)% and ℬ(𝐷+𝑠→𝜂′𝑒+𝜈𝑒)=(0.810±0.038stat±0.024syst)%. Combining these results with the ℬ(𝐷+→𝜂𝑒+𝜈𝑒) and ℬ(𝐷+→𝜂′𝑒+𝜈𝑒) obtained from previous BESIII measurements, the 𝜂−𝜂′ mixing angle in the quark flavor basis is determined to be 𝜙P=(40.0±2.0stat±0.6syst)°. Moreover, from the fits to the partial decay rates of 𝐷+𝑠→𝜂𝑒+𝜈𝑒 and 𝐷+𝑠→𝜂′𝑒+𝜈𝑒, the products of the hadronic transition form factors 𝑓𝜂(′)+(0) and the modulus of the 𝑐→𝑠 Cabibbo-Kobayashi-Maskawa matrix element |𝑉𝑐𝑠| are determined by using different hadronic transition form factor parametrizations. Based on the two-parameter series expansion, the products 𝑓𝜂+(0)|𝑉𝑐𝑠| = 0.4519±0.0071stat±0.0065syst and 𝑓𝜂′+(0)|𝑉𝑐𝑠| = 0.525±0.024stat±0.009syst are extracted. All results determined in this work supersede those measured in the previous BESIII analyses based on the 3.19 fb−1 subsample of data at 4.178 GeV.
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.
A precision measurement of the matrix elements for η→π+π−π0 and η→π0π0π0 decays is performed using a sample of (10087±44)×106 J/ψ decays collected with the BESIII detector. The decay J/ψ→γη is used to select clean samples of 631,686 η→π+π−π0 decays and 272,322 η→π0π0π0 decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The non-zero gX2Y term for the decay mode η→π+π−π0 is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the η→π+π−π0 decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the η→π0π0π0 decay, and no obvious structure around the π+π− mass threshold is observed.
Using (10087±44)×106 J/ψ events collected with the BESIII detector, the radiative hyperon decay Σ→pγ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be (0.996±0.021stat.±0.018syst.)×10−3, which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be −0.652±0.056stat.±0.020syst.. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.
Using (10087±44)×106 J/ψ events collected with the BESIII detector, the radiative hyperon decay Σ→pγ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be (0.996±0.021stat.±0.018syst.)×10−3, which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be −0.652±0.056stat.±0.020syst.. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.
Using (10087±44)×106 J/ψ events collected with the BESIII detector, the radiative hyperon decay Σ→pγ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be (0.996±0.021stat.±0.018syst.)×10−3, which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be −0.652±0.056stat.±0.020syst.. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.
With data samples collected with the BESIII detector at seven energy points at √s = 3.68 − 3.71 GeV, corresponding to an integrated luminosity of 333 pb−1, we present a study of the Λ transverse polarization in the e+e− → ΛΛ¯ reaction. The signifcance of polarization by combining the seven energy points is found to be 2.6σ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the ΛΛ¯ helicity states. The modulus ratio and the relative phase of EM-psionic form factors combined with all energy points are measured to be RΨ = 0.71+0.10−0.10 ± 0.03 and ∆ΦΨ = 23+8.8−8.0 ± 1.6◦, where the frst uncertainties are statistical and the second systematic.
The Born cross sections of the process e+e−→D∗0D∗−π+ at center-of-mass energies from 4.189 to 4.951 GeV are measured for the first time. The data samples used correspond to an integrated luminosity of 17.9fb−1 and were collected by the BESIII detector operating at the BEPCII storage ring. Three enhancements around 4.20, 4.47 and 4.67 GeV are visible. The resonances have masses of 4209.6±4.7±5.9MeV/c2, 4469.1±26.2±3.6MeV/c2 and 4675.3±29.5±3.5MeV/c2 and widths of 81.6±17.8±9.0MeV, 246.3±36.7±9.4MeV, and 218.3±72.9±9.3MeV, respectively, where the first uncertainties are statistical and the second systematic. The first and third resonances are consistent with the ψ(4230) and ψ(4660) states, respectively, while the second one is compatible with the ψ(4500) observed in the e+e−→K+K−J/ψ process. These three charmoniumlike ψ states are observed in e+e−→D∗0D∗−π+ process for the first time.
Observation of three charmonium-like states with JPC = 1⁻⁻ in e⁺e⁻− → D*⁰D*⁻π⁺ + c.c. process
(2023)
The Born cross sections of the process e+e−→D∗0D∗−π++c.c. at center-of-mass energies from 4.189 to 4.951 GeV are measured for the first time. The data samples used correspond to an integrated luminosity of 17.9fb−1 and were collected by the BESIII detector operating at the BEPCII storage ring. Three enhancements around 4.20, 4.47 and 4.67 GeV are visible. The resonances have masses of 4209.6±4.7±5.9MeV/c2, 4469.1±26.2±3.6MeV/c2 and 4675.3±29.5±3.5MeV/c2 and widths of 81.6±17.8±9.0MeV, 246.3±36.7±9.4MeV and 218.3±72.9±9.3MeV, respectively, where the first uncertainties are statistical and the second systematic. The first and third resonances are consistent with the Y(4230) and Y(4660) states, respectively, while the second one is compatible with the Y(4500) observed in the e+e−→K+K−J/ψ process. These three Y states are observed in e+e−→D∗0D∗−π++c.c. process for the first time.
The Born cross sections of the process e+e−→D∗0D∗−π+ at center-of-mass energies from 4.189 to 4.951 GeV are measured for the first time. The data samples used correspond to an integrated luminosity of 17.9fb−1 and were collected by the BESIII detector operating at the BEPCII storage ring. Three enhancements around 4.20, 4.47 and 4.67 GeV are visible. The resonances have masses of 4209.6±4.7±5.9MeV/c2, 4469.1±26.2±3.6MeV/c2 and 4675.3±29.5±3.5MeV/c2 and widths of 81.6±17.8±9.0MeV, 246.3±36.7±9.4MeV, and 218.3±72.9±9.3MeV, respectively, where the first uncertainties are statistical and the second systematic. The first and third resonances are consistent with the ψ(4230) and ψ(4660) states, respectively, while the second one is compatible with the ψ(4500) observed in the e+e−→K+K−J/ψ process. These three charmoniumlike ψ states are observed in e+e−→D∗0D∗−π+ process for the first time.