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The cross sections of the e+e−→ϕη′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn, and decrease as the center-of-mass energy increases as s−n/2 with n=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of n=3.5±0.9. In addition, the charmless decay ψ(3770)→ϕη′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of B(ψ(3770)→ϕη′) at the 90\% confidence level is determined to be 2.3×10−5.
The cross sections of the e+e−→ϕη′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn, and decrease as the center-of-mass energy increases as s−n/2 with n=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of n=3.5±0.9. In addition, the charmless decay ψ(3770)→ϕη′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of B(ψ(3770)→ϕη′) at the 90\% confidence level is determined to be 2.3×10−5.
Based on 4.4 fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure W-exchange decay Λ+c→Ξ0K+ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be αΞ0K+=0.01±0.16(stat.)±0.03(syst.). This result reflects the interference between the S- and P-wave amplitudes. The phase shift between S- and P-wave amplitudes is δp−δs=−1.55±0.25(stat.)±0.05(syst.) rad.
Based on 4.4 fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure W-exchange decay Λ+c→Ξ0K+ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be αΞ0K+=0.01±0.16(stat.)±0.03(syst.). This result reflects the interference between the S- and P-wave amplitudes. The phase shift between S- and P-wave amplitudes is δp−δs=−1.55±0.25(stat.)±0.05(syst.) rad.
We present cross sections for the reaction e+e−→K0SK0L at center-of-mass energies ranging from 3.51 GeV to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb−1. The ratio of neutral-to-charged kaon form factors at large momentum transfers (12 GeV2<Q2<25 GeV2) is determined to be 0.21±0.01, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and consequently excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction |F(π±)|/|F(K±)|=f2π/f2K, where F(π±) and F(K±) are the form factors, and fπ and fK are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay ψ(3770)→K0SK0L for the first time. Within a 1σ contour of the likelihood value, the the branching fraction for ψ(3770)→K0SK0L is determined to be B=(2.63+1.40−1.59)×10−5, and the relative phase between the continuum and ψ(3770) amplitudes is ϕ=(−0.39+0.05−0.10)π. The branching fraction is in good agreement with the S- and D-wave charmonia mixing scheme proposed in the interpretation of the "ρπ puzzle" between J/ψ and ψ(3686) decays.
Based on data samples collected with the BESIII detector at the BEPCII collider, the process e+e−→Σ+Σ¯− is studied at center-of-mass energies s√ = 2.3960, 2.6454, and 2.9000~GeV. Using a fully differential angular description of the final state particles, the complete information of the Σ+ electromagnetic form factors in the time-like region is extracted. The relative phase between the electric and magnetic form factors is determined to be sinΔΦ = -0.67~±~0.29~(stat.)~±~0.18~(syst.) at s√ = 2.3960~GeV, ΔΦ = 55∘~±~19∘~(stat.) ±~14∘~(syst.) at s√ = 2.6454~GeV, and 78∘~±~22∘~(stat.) ±~9∘~(syst.) at s√ = 2.9000~GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.
The processes hc→γP(P=η′, η, π0) are studied with a sample of (27.12±0.14)×108 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The decay hc→γη is observed for the first time with the significance of 9.0σ, and the branching fraction is determined to be (3.77±0.55±0.13±0.26)×10−4, while B(hc→γη′) is measured to be (1.40±0.11±0.04±0.10)×10−3, where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ(3686)→π0hc. The combination of these results allows for a precise determination of Rhc=B(hc→γη)B(hc→γη′), which is calculated to be (27.0±4.4±1.0)%. The results are valuable for gaining a deeper understanding of η−η′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay hc→γπ0, and an upper limit is placed on its branching fraction of B(hc→γπ0)<5.0×10−5, at the 90% confidence level.
We present measurements of the Born cross sections for the processes e+e−→ωχc1 and ωχc2 at center-of-mass energies s√ from 4.308 to 4.951 GeV. The measurements are performed with data samples corresponding to an integrated luminosity of 11.0 fb−1 collected with the BESIII detector operating at the BEPCII storage ring. Assuming the e+e−→ωχc2 signals come from a single resonance, the mass and width are determined to be M=(4413.6±9.0±0.8) MeV/c2 and Γ=(110.5±15.0±2.9) MeV, respectively, which is consistent with the parameters of the well-established resonance ψ(4415). In addition, we also use one single resonance to describe the e+e−→ωχc1 lineshape, and determine the mass and width to be M=(4544.2±18.7±1.7) MeV/c2 and Γ=(116.1±33.5±1.7) MeV, respectively. The structure of this lineshape, observed for the first time, requires further understanding.
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.
Based on data samples collected with the BESIII detector at the BEPCII collider, the process e+e−→Σ+Σ¯− is studied at center-of-mass energies s√ = 2.3960, 2.6454, and 2.9000~GeV. Using a fully differential angular description of the final state particles, the complete information of the Σ+ electromagnetic form factors in the time-like region is extracted. The relative phase between the electric and magnetic form factors is determined to be sinΔΦ = -0.67~±~0.29~(stat.)~±~0.18~(syst.) at s√ = 2.3960~GeV, ΔΦ = 55∘~±~19∘~(stat.) ±~14∘~(syst.) at s√ = 2.6454~GeV, and 78∘~±~22∘~(stat.) ±~9∘~(syst.) at s√ = 2.9000~GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.
Based on a data set of (27.12±0.10)×108 ψ(3686) events collected at the BESIII experiment, the absolute branching fractions of the three dominant Ω− decays are measured to be BΩ−→Ξ0π−=(25.03±0.44±0.53)%, BΩ−→Ξ−π0=(8.43±0.52±0.28)%, and BΩ−→ΛK−=(66.3±0.8±2.0)%, where the first and second uncertainties are statistical and systematic, respectively. The ratio between BΩ−→Ξ0π− and BΩ−→Ξ−π0 is determined to be 2.97±0.19±0.11, which is in good agreement with the PDG value of 2.74±0.15, but greater by more than four standard deviations than the theoretical prediction of 2 obtained from the ΔI=1/2 rule.
Using data samples collected with the BESIII detector at the BEPCII collider at center-of-mass energies ranging from 3.80 to 4.95 GeV, corresponding to an integrated luminosity of 20 fb−1, a measurement of Born cross sections for the e+e−→D0D¯0 and D+D− processes is presented with unprecedented precision. Many clear peaks in the line shape of e+e−→D0D¯0 and D+D− around the mass range of G(3900), ψ(4040), ψ(4160), Y(4260), and ψ(4415), etc., are foreseen. These results offer crucial experimental insights into the nature of hadron production in the open-charm region.
Based on a data sample of (27.08±0.14)×108 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the M1 transition ψ(3686)→γηc(2S) with ηc(2S)→KK¯π is studied, where KK¯π is K+K−π0 or K0SK±π∓. The mass and width of the ηc(2S) are measured to be (3637.8±0.8(stat)±0.2(syst)) MeV/c2 and (10.5±1.7(stat)±3.5(syst)) MeV, respectively. The product branching fraction B(ψ(3686)→γηc(2S))×B(ηc(2S)→KK¯π) is determined to be (0.97±0.06(stat)±0.09(syst))×10−5. Using BR(ηc(2S)→KK¯π)=(1.86+0.68−0.49)%, we obtain the branching fraction of the radiative transition to be BR(ψ(3686)→γηc(2S))=(5.2±0.3(stat)±0.5(syst)+1.9−1.4(extr))×10−4, where the third uncertainty is due to the quoted BR(ηc(2S)→KK¯π).
Using data samples collected at center-of-mass energies between 2.000 and 3.080 GeV with the BESIII detector operating at the BEPCII collider, a partial-wave analysis is performed on the process e+e−→ηπ+π−. In addition to the dominant e+e−→ρη component, the e+e−→a2(1320)π process is also sizeable, contributing up to 24% of the total reaction. The measured cross sections of the process e+e−→ηπ+π− are systematically higher than those of BaBar by more than 3σ at center-of-mass energies between 2.000 and 2.300 GeV. In the cross section lineshape for e+e−→a2(1320)π, a resonant structure is observed with a significance of 5.5σ, with M=(2044±31±4) MeV/c2, Γ=(163±69±24) MeV and BR⋅ΓRe+e−=(34.6±17.1±6.0) eV or (137.1±73.3±2.1) eV. In the cross section lineshape for e+e−→ρη, an evidence of a dip structure around 2180 MeV/c2 is observed with statistical significance of 3.0σ.
The Born cross sections of the process e+e−→D∗0D∗−π+ at center-of-mass energies from 4.189 to 4.951 GeV are measured for the first time. The data samples used correspond to an integrated luminosity of 17.9fb−1 and were collected by the BESIII detector operating at the BEPCII storage ring. Three enhancements around 4.20, 4.47 and 4.67 GeV are visible. The resonances have masses of 4209.6±4.7±5.9MeV/c2, 4469.1±26.2±3.6MeV/c2 and 4675.3±29.5±3.5MeV/c2 and widths of 81.6±17.8±9.0MeV, 246.3±36.7±9.4MeV, and 218.3±72.9±9.3MeV, respectively, where the first uncertainties are statistical and the second systematic. The first and third resonances are consistent with the ψ(4230) and ψ(4660) states, respectively, while the second one is compatible with the ψ(4500) observed in the e+e−→K+K−J/ψ process. These three charmoniumlike ψ states are observed in e+e−→D∗0D∗−π+ process for the first time.
We report the measurement of the inclusive cross sections for e+e−→nOCH (where nOCH denotes non-open charm hadrons) with improved precision at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe three resonances: R(3760), R(3780), and R(3810) with significances of 8.1σ, 13.7σ, and 8.8σ, respectively. The R(3810) state is observed for the first time, while the R(3760) and R(3780) states are observed for the first time in the nOCH cross sections. Two sets of resonance parameters describe the energy-dependent line shape of the cross sections well. In set I [set II], the R(3810) state has mass (3805.7±1.1±2.7) [(3805.7±1.1±2.7)] MeV/c2, total width (11.6±2.9±1.9) [(11.5±2.8±1.9)] MeV, and an electronic width multiplied by the nOCH decay branching fraction of (10.9±3.8±2.5) [(11.0±3.4±2.5)] eV. In addition, we measure the branching fractions B[R(3760)→nOCH]=(25.2±16.1±30.4)%[(6.4±4.8±7.7)%] and B[R(3780)→nOCH]=(12.3±6.6±8.3)%[(10.4±4.8±7.0)%] for the first time. The R(3760) state can be interpreted as an open-charm (OC) molecular state, but containing a simple four-quark state component. The R(3810) state can be interpreted as a hadrocharmonium state.
Using a sample of about 10 billion J/ψ events with the BESIII detector, we search for the weak decays of J/ψ→D¯0π0+c.c., J/ψ→D¯0η+c.c., J/ψ→D¯0ρ0+c.c., J/ψ→D−π++c.c., and J/ψ→D−ρ++c.c.. Since no significant signal is observed, we set the upper limits of the branching fractions of these decays to be B(J/ψ→D¯0π0+c.c.)<4.7×10−7, B(J/ψ→D¯0η+c.c.)<6.8×10−7, B(J/ψ→D¯0ρ0+c.c.)<5.2×10−7, B(J/ψ→D−π++c.c.)<7.0×10−8, and B(J/ψ→D−ρ++c.c.)<6.0×10−7 at the 90\% confidence level.
Improved measurement of the decays η′ → π⁺π⁻π⁺⁽⁰⁾π⁻⁽⁰⁾ and search for the rare decay η′ → 4π⁰
(2024)
Using a sample of 10 billion J/ψ events collected with the BESIII detector, the decays η′→π+π−π+π−, η′→π+π−π0π0 and η′→4π0 are studied via the process J/ψ→γη′. The branching fractions of η′→π+π−π+π− and η′→π+π−π0 π0 are measured to be (8.56±0.25(stat.)±0.23(syst.))×10−5 and (2.12±0.12(stat.)±0.10(syst.))×10−4, respectively, which are consistent with previous measurements but with improved precision. No significant η′→4π0 signal is observed, and the upper limit on the branching fraction of this decay is determined to be less than 1.24×10−5 at the 90% confidence level. In addition, an amplitude analysis of η′→π+π−π+π− is performed to extract the doubly virtual isovector form factor α for the first time. The measured value of α=1.22±0.33(stat.)±0.04(syst.), is in agreement with the prediction of the VMD model.
Using a data sample of (10087±44)×106 J/ψ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process J/ψ→e+e−η(1405) is observed via the decay η(1405)→π0f0(980), f0(980)→π+π−, with a significance of about 9.6σ. The branching fraction of this decay is measured to be B(J/ψ→e+e−π0η(1405)→e+e−π0f0(980)→e+e−π0π+π−)=(2.02±0.24(stat.)±0.09(syst.))×10−7. The branching-fraction ratio B(J/ψ→e+e−η(1405))/B(J/ψ→γη(1405)) is determined to be (1.35±0.19(stat.)±0.06(syst.))×10−2. Furthermore, an e+e− invariant-mass dependent transition form factor of J/ψ→e+e−η(1405) is presented for the first time. The obtained result provides input for different theoretical models, and is valuable for the improved understanding the intrinsic structure of the η(1405) meson.
With a data sample corresponding to an integrated luminosity of 11.5~fb−1 collected with the BESIII detector operating at the BEPCII storage ring, for the first time the light hadron decay χc1(3872)→π+π−η is searched for. While no significant signal is observed, the upper limits at the 90\% confidence level for σ[e+e−→γχc1(3872)]B[χc1(3872)→π+π−η] at center-of-mass energies from 4.13 to 4.34 GeV are determined. By normalizing to the χc1(3872)→π+π−J/ψ decay channel, a 90\% confidence level upper limit for the branching fraction ratio R=B[χc1(3872)→π+π−η]/B[χc1(3872)→π+π−J/ψ]<0.12 is given. These measurements provide important inputs for understanding the internal structure of the χc1(3872) resonance.