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Institute
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.
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.
Using 2.93 fb−1 of e+e− collision data collected with the BESIII detector at the center-of-mass energy 3.773 GeV, we perform the first amplitude analysis of the decay D+ → π+π0π0 and determine the relative magnitudes and phases of different intermediate processes. The absolute branching fraction of D+ → π+π0π0 is measured to be (2.888 ± 0.058stat. ± 0.069syst.)%. The dominant intermediate processes are D+ → a1(1260)+(→ ρ+π0) and D+ → *0ρ+, with branching fractions of (8.66 ± 1.04stat. ± 1.39syst.) × 10−3 and (9.70 ± 0.81stat. ± 0.53syst.) × 10−3, respectively.
By analyzing e+e− annihilation da ta corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with the \text{BESIII} detector, the first observation of the semileptonic decays D0→K0Sπ−π0e+νe and D+→K0Sπ+π−e+νe is reported. With a dominant hadronic contribution from K1(1270), the branching fractions are measured to be B(D0→K1(1270)−(→K0Sπ−π0)e+νe) = (1.69+0.53−0.46±0.15)×10−4 and B(D+→K¯1(1270)0(→K0Sπ+π−)e+νe) = (1.47+0.45−0.40±0.20)×10−4 with statistical significance of 5.4σ and 5.6σ, respectively. When combined with measurements of the K1(1270)→K+π−π decays, the absolute branching fractions are determined to be B(D0→K1(1270)−e+νe) = (1.05+0.33−0.28±0.12±0.12)×10−3 and B(D+→K¯1(1270)0e+νe) = (1.29+0.40−0.35±0.18±0.15)×10−3. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainties originate from the assumed branching fractions of the K1(1270)→Kππ decays.
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.
Quantum-correlated DD¯ 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.
Using 𝑒+𝑒− collision data corresponding to an integrated luminosity of 7.33 fb−1 recorded by the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV, we present an analysis of the decay 𝐷+𝑠→𝜋+𝜋−𝑒+𝜈𝑒, where the 𝐷+𝑠 is produced via the process 𝑒+𝑒−→𝐷*±𝑠𝐷∓𝑠. We observe the 𝑓0(980) in the 𝜋+𝜋− system and the branching fraction of the decay 𝐷+𝑠→𝑓0(980)𝑒+𝜈𝑒 with 𝑓0(980)→𝜋+𝜋− measured to be (1.72±0.13stat±0.10syst)×10−3, where the uncertainties are statistical and systematic, respectively. The dynamics of the 𝐷+𝑠→𝑓0(980)𝑒+𝜈𝑒 decay are studied with the simple pole parametrization of the hadronic form factor and the Flatté formula describing the 𝑓0(980) in the differential decay rate, and the product of the form factor 𝑓𝑓0+(0) and the 𝑐→𝑠 Cabibbo-Kobayashi-Maskawa matrix element |𝑉𝑐𝑠| is determined for the first time to be 𝑓𝑓0+(0)|𝑉𝑐𝑠|=0.504±0.017stat±0.035syst. Furthermore, the decay 𝐷+
𝑠→𝑓0(500)𝑒+𝜈𝑒 is searched for the first time but no signal is found. The upper limit on the branching fraction of 𝐷+𝑠→𝑓0(500)𝑒+𝜈𝑒, 𝑓0(500)→𝜋+𝜋− decay is set to be 3.3×10−4 at 90% confidence level.
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 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.
The process e+e−→D∗+sD∗−s is studied with a semi-inclusive method using data samples at center-of-mass energies from threshold to 4.95 GeV collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections of the process are measured for the first time with high precision in this energy region. Two resonance structures are observed in the energy-dependent cross sections around 4.2 and 4.4 GeV. By fitting the cross sections with a coherent sum of three Breit-Wigner amplitudes and one phase-space amplitude, the two significant structures are assigned masses of (4186.5±9.0±30) MeV/c2 and (4414.5±3.2±6.0) MeV/c2, widths of (55±17±53) MeV and (122.6±7.0±8.2) MeV, where the first errors are statistical and the second ones are systematic. The inclusion of a third Breit-Wigner amplitude is necessary to describe a structure around 4.79 GeV.