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Institute
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.
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 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.
Based on (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII collider, a partial wave analysis of the decay J/ψ→ϕπ0η is performed. We observe for the first time two new structures on the ϕη invariant mass distribution, with statistical significances of 24.0σ and 16.9σ; the first with JPC = 1+−, mass M = (1911 ± 6 (stat.) ± 14 (sys.))~MeV/c2, and width Γ= (149 ± 12 (stat.) ± 23 (sys.))~MeV, the second with JPC = 1−−, mass M = (1996 ± 11 (stat.) ± 30 (sys.))~MeV/c2, and width Γ = (148 ± 16 (stat.) ± 66 (sys.))~MeV. These measurements provide important input for the strangeonium spectrum. In addition, the f0(980)−a0(980)0 mixing signal in J/ψ→ϕf0(980)→ϕa0(980)0 and the corresponding electromagnetic decay J/ψ→ϕa0(980)0 are measured with improved precision, providing crucial information to understand the nature of a0(980)0 and f0(980).
Based on (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII collider, a partial wave analysis of the decay J/ψ→ϕπ0η is performed. We observe for the first time two new structures on the ϕη invariant mass distribution, with statistical significances of 24.0σ and 16.9σ; the first with JPC = 1+−, mass M = (1911 ± 6 (stat.) ± 14 (sys.))~MeV/c2, and width Γ= (149 ± 12 (stat.) ± 23 (sys.))~MeV, the second with JPC = 1−−, mass M = (1996 ± 11 (stat.) ± 30 (sys.))~MeV/c2, and width Γ = (148 ± 16 (stat.) ± 66 (sys.))~MeV. These measurements provide important input for the strangeonium spectrum. In addition, the f0(980)−a0(980)0 mixing signal in J/ψ→ϕf0(980)→ϕa0(980)0 and the corresponding electromagnetic decay J/ψ→ϕa0(980)0 are measured with improved precision, providing crucial information to understand the nature of a0(980)0 and f0(980).
The Born cross sections for the process e+e−→ωη′ are measured at 22 center-of-mass energies from 2.000 to 3.080 GeV using data collected with the BESIII detector at the BEPCII collider. A resonant structure is observed with a statistical significance of 9.6σ. A Breit-Wigner fit determines its mass to be MR=(2153±30±31) MeV/c2 and its width to be ΓR=(167±77±7) MeV, where the first uncertainties are statistical and the second are systematic.
Evidence for the singly Cabibbo suppressed decay Λ+c→pπ0 is reported for the first time with a statistical significance of 3.7σ based on 6.0 fb−1 of e+e− collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Λ+c→pπ0 is measured to be (1.56+0.72−0.58±0.20)×10−4. Combining with the branching fraction of Λ+c→nπ+, (6.6±1.3)×10−4, the ratio of the branching fractions of Λ+c→nπ+ and Λ+c→pπ0 is calculated to be 3.2+2.2−1.2. As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the non-factorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Λ+c→pη is measured to be (1.63±0.31stat±0.11syst)×10−3.
A light scalar X0 or vector X1 particles have been introduced as a possible explanation for the (g−2)μ anomaly and dark matter phenomena.
Using (8.998±0.039)×109 $\jpsi$ events collected by the BESIII detector, we search for a light muon philic scalar X0 or vector X1 in the processes J/ψ→μ+μ−X0,1 with X0,1 invisible decays. No obvious signal is found, and the upper limits on the coupling g′0,1 between the muon and the X0,1 particles are set to be between 1.1×10−3 and 1.0×10−2 for the X0,1 mass in the range of 1<M(X0,1)<1000~MeV/c2 at 90% confidence level.
A light scalar X0 or vector X1 particles have been introduced as a possible explanation for the (g−2)μ anomaly and dark matter phenomena.
Using (8.998±0.039)×109 $\jpsi$ events collected by the BESIII detector, we search for a light muon philic scalar X0 or vector X1 in the processes J/ψ→μ+μ−X0,1 with X0,1 invisible decays. No obvious signal is found, and the upper limits on the coupling g′0,1 between the muon and the X0,1 particles are set to be between 1.1×10−3 and 1.0×10−2 for the X0,1 mass in the range of 1<M(X0,1)<1000 MeV/c2 at 90% confidence level.