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Based on 10 billion J/ψ events collected at the BESIII experiment, a search for CP violation in Λ decay is performed in the difference between CP-odd decay parameters α− for Λ→pπ− and α+ for Λ¯→p¯π+ by using the process e+e−→J/ψ→ΛΛ¯. With a five-dimensional fit to the full angular distributions of the daughter baryon, the most precise values for the decay parameters are determined to be α−=0.7519±0.0036±0.0024 and α+=−0.7559±0.0036±0.0030, respectively. The Λ and Λ¯ averaged value of the decay parameter is extracted to be αavg=0.7542±0.0010±0.0024 with unprecedented accuracy. The CP asymmetry ACP=(α−+α+)/(α−−α+) is determined to be −0.0025 ± 0.0046 ± 0.0012, which is one of the most precise measurements in the baryon sector. The reported results for the decay parameter will play an important role in the studies of the polarizations and CP violations for the strange, charmed and beauty baryons.
The cross sections of e+e−→K+K−J/ψ at center-of-mass energies from 4.127 to 4.600 GeV are measured based on 15.6 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in the line shape of the cross sections. The mass and width of the first structure are measured to be (4225.3 ± 2.3 ± 21.5) MeV and (72.9±6.1±30.8) MeV, respectively. They are consistent with those of the established Y(4230). The second structure is observed for the first time with a statistical significance greater than 8σ, denoted as Y(4500). Its mass and width are determined to be (4484.7 ± 13.3 ± 24.1) MeV and (111.1 ± 30.1 ± 15.2) MeV, respectively. The first presented uncertainties are statistical and the second ones are systematic. The product of the electronic partial width with the decay branching fraction Γ(Y(4230)→e+e−)B(Y(4230) → K+K−J/ψ) is reported.
The cross sections of e+e−→K+K−J/ψ at center-of-mass energies from 4.127 to 4.600~GeV are measured based on 15.6 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in the line shape of the cross sections. The mass and width of the first structure are measured to be (4225.3±2.3±21.5) MeV and (72.9±6.1±30.8)~MeV, respectively. They are consistent with those of the established Y(4230). The second structure is observed for the first time with a statistical significance greater than 8σ, denoted as Y(4500). Its mass and width are determined to be (4484.7±13.3±24.1) MeV and (111.1±30.1±15.2) MeV, respectively. The first presented uncertainties are statistical and the second ones are systematic. The product of the electronic partial width with the decay branching fraction Γ(Y(4230)→e+e−)B(Y(4230)→K+K−J/ψ) is reported.
The cross sections of e+e−→K+K−J/ψ at center-of-mass energies from 4.127 to 4.600~GeV are measured based on 15.6 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in the line shape of the cross sections. The mass and width of the first structure are measured to be (4225.3±2.3±21.5) MeV and (72.9±6.1±30.8)~MeV, respectively. They are consistent with those of the established Y(4230). The second structure is observed for the first time with a statistical significance greater than 8σ, denoted as Y(4500). Its mass and width are determined to be (4484.7±13.3±24.1) MeV and (111.1±30.1±15.2) MeV, respectively. The first presented uncertainties are statistical and the second ones are systematic. The product of the electronic partial width with the decay branching fraction Γ(Y(4230)→e+e−)B(Y(4230)→K+K−J/ψ) is reported.
Based on (10087±44)×106 𝐽/𝜓 events collected with the BESIII detector at BEPCII, the double Dalitz decay 𝜂′→𝑒+𝑒−𝑒+𝑒− is observed for the first time via the 𝐽/𝜓→𝛾𝜂′ decay process. The significance is found to be 5.7𝜎 with systematic uncertainties taken into consideration. Its branching fraction is determined to be ℬ(𝜂′→𝑒+𝑒−𝑒+𝑒−)=(4.5±1.0(stat)±0.5(sys))×10−6.
Observation of a near-threshold structure in the K⁺ recoil-mass spectra in e⁺e⁻ → K⁺(Dₛ⁻D*⁰+Dₛ*⁻D⁰)
(2021)
We report a study of the processes of 𝑒+𝑒−→𝐾+𝐷−𝑠𝐷*0 and 𝐾+𝐷*−𝑠𝐷0 based on 𝑒+𝑒− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess of events over the known contributions of the conventional charmed mesons is observed near the 𝐷−𝑠𝐷*0 and 𝐷*−𝑠𝐷0 mass thresholds in the 𝐾+ recoil-mass spectrum for events collected at √𝑠=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8
−2.6±2.1) MeV/𝑐2 and (12.8+5.3−4.4±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 𝜎 over the contributions only from the conventional charmed mesons. This is the first candidate for a charged hidden-charm tetraquark with strangeness, decaying into 𝐷−𝑠𝐷*0 and 𝐷*−𝑠𝐷0. However, the properties of the excess need further exploration with more statistics.
We report a study of the processes of e+e−→K+(D−sD∗0+D∗−sD0) based on e+e− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess over the known contributions of the conventional charmed mesons is observed near the D−sD∗0 and D∗−sD0 mass thresholds in the K+ recoil-mass spectrum for events collected at s√=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8−2.6±2.1) MeV/c2 and (12.8+5.3−4.4±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 σ over the pure contributions from the conventional charmed mesons. This is the first candidate of the charged hidden-charm tetraquark with strangeness, decaying into D−sD∗0 and D∗−sD0. However, the genuine properties of the excess need further exploration with more statistics.
We report a study of the processes of e+e−→K+(D−sD∗0+D∗−sD0) based on e+e− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess over the known contributions of the conventional charmed mesons is observed near the D−sD∗0 and D∗−sD0 mass thresholds in the K+ recoil-mass spectrum for events collected at s√=4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8−2.6±2.1) MeV/c2 and (12.8+5.3−4.4±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 σ over the contributions only from the conventional charmed mesons. This is the first candidate of the charged hidden-charm tetraquark with strangeness, decaying into D−sD∗0 and D∗−sD0. However, the properties of the excess need further exploration with more statistics.
Using e+e− annihilation data sets corresponding to an integrated luminosity of 4.5 fb−1, collected with the BESIII detector at center-of-mass energies between 4.600 and 4.699 GeV, we report the first measurements of the absolute branching fractions B(Λ+c→pK0L)=(1.67±0.06±0.04)%, B(Λ+c→pK0Lπ+π−)=(1.69±0.10±0.05)%, and B(Λ+c→pK0Lπ0)=(2.02±0.13±0.05)%, where the first uncertainties are statistical and the second systematic. Combining with the known branching fractions of Λ+c→pK0S, Λ+c→pK0Sπ+π−, and Λ+c→pK0Sπ0, we present the first measurements of the K0S-K0L asymmetries R(Λ+c,K0S,LX)=B(Λ+c→K0SX)−B(Λ+c→K0LX)B(Λ+c→K0SX)+B(Λ+c→K0LX) in charmed baryon decays: R(Λ+c,pK0S,L)=−0.025±0.031, R(Λ+c,pK0S,Lπ+π−)=−0.027±0.048, and R(Λ+c,pK0S,Lπ0)=−0.015±0.046. No significant asymmetries within the uncertainties are observed.
The singly Cabibbo-suppressed decay D+s → K+π+π−π0 is observed by using a data set corresponding to an integrated luminosity of 6.32 fb−1 recorded by the BESIII detector at the centre-of-mass energies between 4.178 and 4.226 GeV. The first amplitude analysis of D+s → K+π+π−π0 reveals the sub-structures in this decay and determines the fractions and relative phases of different intermediate processes. The dominant intermediate process is D+s → K∗0ρ+, with a fit fraction of (40.5 ± 2.8stat. ± 1.5syst.)%. With the detection efficiency based on our amplitude analysis, the absolute branching fraction forD+s → K+π+π−π0 is measured to be (9.75 ± 0.54stat. ± 0.17syst.) × 10−3.