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We measure the Born cross section for the reaction e+e−→ηhc from s√=4.129 to 4.600~GeV using data sets collected by the BESIII detector running at the BEPCII collider. A resonant structure in the cross section line shape near 4.200~GeV is observed with a statistical significance of 7σ. The parameters of this resonance are measured to be \MeasMass\ and \MeasWidth, where the first uncertainties are statistical and the second systematic.
he Born cross sections for the process 𝑒+𝑒−→𝜂′𝜋+𝜋− at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of 6.3𝜎 and a mass and width of 𝑀=(2111±43±25) MeV/𝑐2 and Γ=(135±34±30) MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in 𝑒+𝑒−→𝜂′𝜋+𝜋− and BESIII in 𝑒+𝑒−→𝜔𝜋0 within two standard deviations.
Using a data sample of (448.1±2.9)×106 𝜓(3686) decays collected at an 𝑒+𝑒− center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay 𝜓(3686)→𝑒+𝑒−𝜂𝑐 with a significance of 7.9𝜎. The branching fraction is determined to be ℬ(𝜓(3686)→𝑒+𝑒−𝜂𝑐)=(3.77±0.40stat±0.18syst)×10−5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the 𝜓(3686) and the 𝜂𝑐, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of 𝜂𝑐 decays.
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 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.
Observation of ηc(2S) → 3(π⁺π⁻) and measurements of χcJ → 3(π⁺π⁻) in ψ(3686) radiative transitions
(2022)
The hadronic decay 𝜂𝑐(2𝑆)→3(𝜋+𝜋−) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 𝜓(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of 𝜂𝑐(2𝑆) are (3643.4±2.3 (stat)±4.4 (syst)) MeV/𝑐2 and (19.8±3.9 (stat)±3.1 (syst)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction ℬ[𝜓(3686)→𝛾𝜂𝑐(2𝑆)]×ℬ[𝜂𝑐(2𝑆)→3(𝜋+𝜋−)] is measured to be (9.2±1.0 (stat)±1.2 (syst))×10−6. Using ℬ[𝜓(3686)→𝛾𝜂𝑐(2𝑆)]=(7.0+3.4−2.5)×10−4, we obtain ℬ[𝜂𝑐(2𝑆)→3(𝜋+𝜋−)]=(1.31±0.15 (stat)±0.17 (syst) (+0.64−0.47) (extr))×10−2, where the third uncertainty is from ℬ[𝜓(3686)→𝛾𝜂𝑐(2𝑆)]. We also measure the 𝜒𝑐𝐽→3(𝜋+𝜋−) (𝐽=0, 1, 2) decays via 𝜓′→𝛾𝜒𝑐𝐽 transitions. The branching fractions are ℬ[𝜒𝑐0→3(𝜋+𝜋−)]=(2.080±0.006 (stat)±0.068 (syst))×10−2, ℬ[𝜒𝑐1→3(𝜋+𝜋−)]=(1.092±0.004 (stat)±0.035 (syst))×10−2, and ℬ[𝜒𝑐2→3(𝜋+𝜋−)]=(1.565±0.005 (stat)±0.048 (syst))×10−2.
Observation of ηc(2S) → 3(π⁺π⁻) and measurements of χcJ → 3(π⁺π⁻) in ψ(3686) radiative transitions
(2022)
The hadronic decay ηc(2S)→3(π+π−) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ηc(2S) are (3643.4±2.3(stat.)±4.4(syst.)) MeV/c2 and (19.8±3.9(stat.)±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[ψ(3686) → γηc(2S)]×B[ηc(2S)→3(π+π−)] is measured to be (9.2±1.0(stat.)±0.9(syst.))×10−6. Using B[ψ(3686)→γηc(2S)]=(7.0+3.4−2.5)×10−4, we obtain B[ηc(2S)→3(π+π−)]=(1.31±0.15(stat.)±0.13(syst.)(+0.64−0.47)(extr))×10−2, where the third uncertainty is from B[ψ(3686)→γηc(2S)]. We also measure the χcJ→3(π+π−) (J=0,1,2) decays via ψ(3686)→γχcJ transitions. The branching fractions are B[χc0→3(π+π−)]=(2.080±0.006(stat.)±0.068(syst.))×10−2, B[χc1→3(π+π−)]=(1.092±0.004(stat.)±0.035(syst.))×10−2, and B[χc2→3(π+π−)]=(1.565±0.005(stat.)±0.048(syst.))×10−2.
Observation of ηc(2S) → 3(π⁺π⁻) and measurements of χcJ → 3(π⁺π⁻) in ψ(3686) radiative transitions
(2022)
The hadronic decay ηc(2S)→3(π+π−) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ηc(2S) are (3643.4±2.3(stat.)±4.4(syst.)) MeV/c2 and (19.8±3.9(stat.)±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[ψ(3686)→γηc(2S)]×B[ηc(2S)→3(π+π−)] is measured to be (9.2±1.0(stat.)±0.9(syst.))×10−6. Using B[ψ(3686)→γηc(2S)]=(7.0+3.4−2.5)×10−4, we obtain B[ηc(2S)→3(π+π−)]=(1.31±0.15(stat.)±0.13(syst.)(+0.64−0.47)(extr))×10−2, where the third uncertainty is from B[ψ(3686)→γηc(2S)]. We also measure the χcJ→3(π+π−) (J=0,1,2) decays via ψ(3686)→γχcJ transitions. The branching fractions are B[χc0→3(π+π−)]=(2.080±0.006(stat.)±0.068(syst.))×10−2, B[χc1→3(π+π−)]=(1.092±0.004(stat.)±0.035(syst.))×10−2, and B[χc2→3(π+π−)]=(1.565±0.005(stat.)±0.048(syst.))×10−2.
The absolute branching fraction of the decay Λc(2625)+→Λ+cπ+π− is measured for the first time to be (50.7±5.0stat.±4.9syst.)% with 368.48 pb−1 of e+e− collision data collected by the BESIII detector at the center-of-mass energies of s√=4.918 and 4.950 GeV. This result is lower than the naive prediction of 67\%, obtained from isospin symmetry, by more than 2σ, thereby indicating that the novel mechanism referred to as the \textit{threshold effect}, proposed for the strong decays of Λc(2595)+, also applies to Λc(2625)+. This measurement is necessary to obtain the coupling constants for the transitions between s-wave and p-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Λc(2595)+→Λ+cπ+π−. No significant signal is observed, and the upper limit on its branching fraction is determined to be 80.8\% at the 90\% confidence level.
We report a measurement of the cross section for the process e+e−→π+π−J/ψ around the X(3872) mass in search for the direct formation of e+e−→X(3872) through the two-photon fusion process. No enhancement of the cross section is observed at the X(3872) peak and an upper limit on the product of electronic width and branching fraction of X(3872)→π+π−J/ψ is determined to be Γee×B(X(3872)→π+π−J/ψ)<7.5×10−3eV at 90% confidence level under an assumption of total width of 1.19±0.21 MeV. This is an improvement of a factor of about 17 compared to the previous limit. Furthermore, using the latest result of B(X(3872)→π+π−J/ψ), an upper limit on the electronic width Γee of X(3872) is obtained to be <0.32eV at the 90% confidence level.
A measurement of the 𝐶𝑃-even fraction of the decay 𝐷0→𝜋+𝜋−𝜋+𝜋− is performed with a quantum-correlated 𝜓(3770)→𝐷¯𝐷 data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93 fb−1. Using a combination of 𝐶𝑃 eigenstates, 𝐷→𝜋+𝜋−𝜋0 and 𝐷→𝐾0𝑆,𝐿𝜋+𝜋− as tagging modes, the 𝐶𝑃-even fraction is measured to be 𝐹4𝜋+=0.735±0.015±0.005, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the angle 𝛾 of the Cabibbo-Kobayashi-Maskawa matrix with 𝐵±→𝐷𝐾± decays, and for time-dependent studies of 𝐶𝑃 violation and mixing in the 𝐷0−¯𝐷0 system.
A measurement of the CP-even fraction of the decay D0→π+π−π+π− is performed with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93 fb−1. Using a combination of CP eigenstates, D→π+π−π0 and D→K0S,Lπ+π− as tagging modes, the CP-even fraction is measured to be F4π+=0.735±0.015±0.005, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the CKM angle γ with B±→DK± decays, and for time-dependent studies of CP violation and mixing in the D0-D¯0 system.
The Born cross sections of the e+e− → D*+D*− and e+e− → D*+D− processes are measured using e+e− collision data collected with the BESIII experiment at center-of-mass energies from 4.085 to 4.600 GeV, corresponding to an integrated luminosity of 15.7 fb−1. The results are consistent with and more precise than the previous measurements by the Belle, Babar and CLEO collaborations. The measurements are essential for understanding the nature of vector charmonium and charmonium-like states.
We report a measurement of the observed cross sections of e+ e− → J/ψX based on 3.21 fb − 1 of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. In analysis of the cross sections, we measured the decay branching fractions of B(ψ(3686) → J/ψX) = (64.4 ± 0.6 ± 1.6)% and B(ψ(3770) → J/ψX) = (0.5 ± 0.2 ± 0.1)% for the first time. The energy-dependent line shape of these cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays ψ (3686) → J/ψX and ψ(3770) → J/ψX. Instead, it can be better described with one more BW amplitude of the decay R(3760)→ J/ψX. Under this assumption, we extracted the R (3760) mass M R (3760 ) = 3766.2 ± 3.8 ± 0.4 MeV/c2, total width Γ tot R ( 3760 ) = 22.2 ± 5.9 ± 1.4 MeV, and product of leptonic width and decay branching fraction
ΓeeR(3760) B[R(3760) → J/ψX] = (79.4 ± 85.5 ± 11.7) eV. The significance of the R(3760) is 5.3σ. The first uncertainties of these measured quantities are from fits to the cross sections and second systematic.
We report the first measurements of the absolute branching fractions of D0 → K0 Lϕ, D0 → K0Lη, D0 → K0Lω, and D0 → K0Lη0, by analyzing 2.93 fb−1 of eþe− collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. Taking the world averages of the branching fractions of D0 → K0Sϕ, D0 → K0Sη, D0 → K0Sω, and D0 → K0Sη0, the K0S − K0L asymmetries RðD0; XÞ in these decay modes are obtained. The CP asymmetries in these decays are also determined. No significant CP violation is observed
Born cross sections for the processes e+e− → ωη and e+e− → ωπ0 have been determined for centerof-mass energies between 2.00 and 3.08 GeV with the BESIII detector at the BEPCII collider. The results obtained in this work are consistent with previous measurements but with improved precision. Two resonant structures are observed. In the e+e− → ωη cross sections, a resonance with a mass of (2176 ± 24 ± 3) MeV/c2 and a width of (89 ± 50 ± 5) MeV is observed with a significance of 6.2σ. Its properties are consistent with the φ(2170). In the e+e− → ωπ0 cross sections, a resonance denoted Y (2040) is observed with a significance of more than 10σ. Its mass and width are determined to be (2034 ± 13 ± 9) MeV/c2 and (234 ± 30 ± 25) MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.
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.
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 e+e− → +¯ − and e+e− → −¯ + processes are determined for centerof-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be described properly by a pQCD function and the resulting ratio of effective form factors for the + and − is consistent with 3. In addition, ratios of the + electric and magnetic form factors, |GE /GM |, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the ± form factors require more theoretical discussions for the hyperons.