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Using data taken at 23 center-of-mass energies between 4.0 and 4.6 GeV with the BESIII detector at the BEPCII collider and with a total integrated luminosity of approximately 15 fb−1, the process e+e−→2(pp¯) is studied for the first time. The Born cross sections for e+e−→2(pp¯) are measured, and no significant structure is observed in the lineshape. The baryon pair (pp and p¯p¯) invariant mass spectra are consistent with phase space, therefore no hexaquark or di-baryon state is found.
Using data taken at 23 center-of-mass energies between 4.0 and 4.6 GeV with the BESIII detector at the BEPCII collider and with a total integrated luminosity of approximately 15 fb−1, the process e+e−→2(pp¯) is studied for the first time. The Born cross sections for e+e−→2(pp¯) are measured, and no significant structure is observed in the lineshape. The baryon pair (pp and p¯p¯) invariant mass spectra are consistent with phase space, therefore no hexaquark or di-baryon state is found.
We search for the process e+e−→π+π−χcJ (J=0,1,2) and for a charged charmonium-like state in the π±χcJ subsystem. The search uses data sets collected with the BESIII detector at the BEPCII storage ring at center-of-mass energies between 4.18 GeV and 4.60 GeV. No significant π+π−χcJ signals are observed at any center-of-mass energy, and thus upper limits are provided which also serve as limits for a possible charmonium-like structure in the invariant π±χcJ mass.
The rare decay 𝜂′→𝜋+𝜋−𝑒+𝑒− is studied using a sample of 1.3×109 𝐽/𝜓 events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be (2.42±0.05stat±0.08syst)×10−3. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the 𝐶𝑃-violating asymmetry in the angle between the decay planes of the 𝜋+𝜋−-pair and the 𝑒+𝑒−-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is 𝒜𝐶𝑃=(2.9±3.7stat±1.1syst)%, which is consistent with the standard model expectation of no 𝐶𝑃-violation. The precision is comparable to the asymmetry measurement in the 𝐾0𝐿→𝜋+𝜋−𝑒+𝑒− decay where the observed (14±2)% effect is driven by a standard model mechanism.
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.
Using 9.9 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.15 and 4.30 GeV, we search for the processes e+e−→γX(3872) with X(3872)→π0χc0 and X(3872)→ππχc0. Depending on the fitting model, the statistical significance for X(3872)→π0χc0 ranges from 1.3σ to 2.8σ. We set upper limits (at 90\% C.L.) of B(X(3872)→π0χc0)B(X(3872)→π+π−J/ψ)<3.6, B(X(3872)→π+π−χc0)B(X(3872)→π+π−J/ψ)<0.68, and B(X(3872)→π0π0χc0)B(X(3872)→π+π−J/ψ)<1.7. Combined with the BESIII measurement of X(3872)→π0χc1, we also set an upper limit of B(X(3872)→π0χc0)B(X(3872)→π0χc1)<4.4.
Using 9.9 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.15 and 4.30 GeV, we search for the processes e+e−→γX(3872) with X(3872)→π0χc0 and X(3872)→ππχc0. Depending on the fitting model, the statistical significance for X(3872)→π0χc0 ranges from 1.3σ to 2.8σ. We set upper limits (at 90\% C.L.) of B(X(3872)→π0χc0)B(X(3872)→π+π−J/ψ)<3.6, B(X(3872)→π+π−χc0)B(X(3872)→π+π−J/ψ)<0.68, and B(X(3872)→π0π0χc0)B(X(3872)→π+π−J/ψ)<1.7. Combined with the BESIII measurement of X(3872)→π0χc1, we also set an upper limit of B(X(3872)→π0χc0)B(X(3872)→π0χc1)<4.4.
Using 9.9 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.15 and 4.30 GeV, we search for the processes e+e−→γX(3872) with X(3872)→π0χc0 and X(3872)→ππχc0. Depending on the fitting model, the statistical significance for X(3872)→π0χc0 ranges from 1.3σ to 2.8σ. We set upper limits (at 90\% C.L.) of B(X(3872)→π0χc0)B(X(3872)→π+π−J/ψ)<3.6, B(X(3872)→π+π−χc0)B(X(3872)→π+π−J/ψ)<0.68, and B(X(3872)→π0π0χc0)B(X(3872)→π+π−J/ψ)<1.7. Combined with the BESIII measurement of X(3872)→π0χc1, we also set an upper limit of B(X(3872)→π0χc0)B(X(3872)→π0χc1)<4.4.
Measurement of e⁺e⁻ → γχc0,c1,c2 cross sections at center-of-mass energies between 3.77 and 4.60 GeV
(2021)
The e+e−→γχcJ (J=0,1,2) processes are studied at center-of-mass energies ranging from 3.773 to 4.600 GeV, using a total integrated luminosity of 19.3 fb−1 e+e− annihilation data accumulated with the BESIII detector at BEPCII. We observe for the first time e+e−→γχc1,c2 signals at s√= 4.180 GeV with statistical significances of 7.6σ and 6.0σ, respectively. The production cross section of e+e−→γχc1,c2 at each center-of-mass energy is also measured. We find that the line shape of the e+e−→γχc1 cross section can be described with conventional charmonium states ψ(3686), ψ(3770), ψ(4040), ψ(4160). Compared with this, for the e+e−→γχc2 channel, one more additional resonance is added to describe the cross section line shape. Its mass and width are measured to be M=4371.7±7.5±1.8 MeV/c2 and Γtot=51.1±17.6±1.9 MeV, where the first uncertainties are statistical and the second systematic. The significance of this resonance is estimated to be 5.8σ, and its parameters agree with the Y(4360) resonance previously reported in e+e−→π+π−ψ(3686), and the Y(4390) in e+e−→π+π−hc within uncertainties. No significant signal for the e+e−→γχc0 process is observed, and the upper limits of Born cross sections σB(e+e−→γχc0) at 90\% confidence level are reported.