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Observation of η_(c)(1S, 2S) and χ_(cJ) decays to 2(π⁺π^(−))η via ψ(3686) radiative transitions
(2024)
Based on 2.7×109 ψ(3686) decays collected with the BESIII detector, the radiative decay ψ(3686)→γ2(π+π−)η is investigated to measure properties of S- and P-wave charmonium states. The branching fraction of the decay ηc(1S)→2(π+π−)η, which is found to have a strong dependence on the interference pattern between ηc(1S) and non-ηc(1S) processes, is measured in both destructive and constructive interference scenarios for the first time. The mass and width of the ηc(1S) are measured to be M=(2984.14±0.13±0.38) MeV/c2 and Γ=(28.82±0.11±0.82) MeV, respectively. Clear signals for the decays of the χcJ(J=0,1,2) and the ηc(2S) to 2(π+π−)η are also observed for the first time, and the corresponding branching fractions are measured. The ratio of the branching fractions between the ηc(2S) and ηc(1S) decays is significantly lower than the theoretical prediction, which might suggest different dynamics in their decays.
Based on e+e− collision data collected at center-of-mass energies from 2.000 to 3.080 GeV by the BESIII detector at the BEPCII collider, a partial wave analysis isperformed for the process e+e− → K0SK0Lπ0. The results allow the Born cross sections of the process e+e− → K0SK0Lπ0, as well as its subprocesses e+e− → K∗(892)0K¯ 0 and K∗2(1430)0K¯ 0 to be measured. The Born cross sections for e+e− → K0SK0 Lπ 0 are consistent with previous measurements by BaBar, but with substantially improved precision. The Born cross section lineshape of the process e+e − → K∗(892)0K¯ 0 is consistent with a vector meson state around 2.2 GeV with a signifcance of 3.2σ. A Breit-Wigner ft determines its mass as MY = (2164.7 ± 9.1 ± 3.1) MeV/c2 and its width as ΓY = (32.4 ± 21.0 ± 1.8) MeV.
Quantum-correlated 𝐷¯𝐷 pairs collected by the BESIII experiment at the 𝜓(3770) resonance corresponding to an integrated luminosity of 2.93 fb−1 are used to study the 𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0 decay mode. The 𝐶𝑃-even fraction of 𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0 decays is determined to be 0.235±0.010±0.002, where the first uncertainty is statistical and the second is systematic.
We report the measurement of the cross sections for e+e−→hadrons at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe a new resonance R(3810) in the cross sections for the first time, and observe the R(3760) resonance with high significance in the cross sections. The R(3810) has a mass of (3804.5±0.9±0.9) ~MeV/c2, a total width of (5.4±3.5±3.2)~MeV, and an electronic partial width of (19.4±7.4±12.1)~eV. Its significance is 7.7σ. The R(3810) could be interpreted as a hadro-charmonium resonance predicted by Quantum Chromodynamics (QCD). In addition, we measure the mass (3751.9±3.8±2.8) ~MeV/c2, the total width (32.8±5.8±8.7)~MeV, and the electronic partial width (184±75±86)~eV with improved precision for the R(3760). Furthermore, for the R(3780) we measure the mass (3778.7±0.5±0.3) ~MeV/c2 and total width (20.3±0.8±1.7)~MeV with improved precision, and the electronic partial width (265±69±83)~eV. The R(3780) can be interpreted as the 13D1 state of charmonium. Its mass and total width differ significantly from the corresponding fitted values given by the Particle Data Group in 2022 by 7.1 and 3.2 times the uncertainties for ψ(3770), respectively. ψ(3770) has been interpreted as the 13D1 state for 45 years.
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.
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).
Using 2.93 fb−1 of e+e− collision data collected with the BESIII detector at the center-of-mass energy of 3.773 GeV, we investigate the semileptonic decays D+→π+π−ℓ+νℓ (ℓ=e and μ). The D+→f0(500)μ+νμ decay is observed for the first time. By analyzing simultaneously the differential decay rates of D+→f0(500)μ+νμ and D+→f0(500)e+νe in different ℓ+νℓ four-momentum transfer intervals, the product of the relevant hadronic form factor ff0+(0) and the magnitude of the c→d Cabibbo-Kobayashi-Maskawa matrix element |Vcd| is determined to be ff0+(0)|Vcd|=0.0787±0.0060stat±0.0033syst for the first time. With the input of |Vcd| from the global fit in the standard model, we determine ff0+(0)=0.350±0.027stat±0.015syst. The absolute branching fractions of D+→f0(500)(π+π−)μ+νμ and D+→ρ0(π+π−)μ+νμ are determined as (0.72±0.13stat±0.10syst)×10−3 and (1.64±0.13stat±0.11syst)×10−3. Combining these results with those of previous BESIII measurements on their semielectronic counterparts from the same data sample, we test lepton flavor universality by measuring the branching fraction ratios BD+→ρ0μ+νμ/BD+→ρ0e+νe=0.88±0.10 and BD+→f0(500)μ+νμ/BD+→f0(500)e+νe = 1.14±0.28, which are compatible with the standard model expectation.
Using 2.93 fb−1 of e+e− collision data collected with the BESIII detector at the center-of-mass energy of 3.773 GeV, we investigate the semileptonic decays D+→π+π−ℓ+νℓ (ℓ=e and μ). The D+→f0(500)μ+νμ decay is observed for the first time. By analyzing simultaneously the differential decay rates of D+→f0(500)μ+νμ and D+→f0(500)e+νe in different ℓ+νℓ four-momentum transfer intervals, the product of the relevant hadronic form factor ff0+(0) and the magnitude of the c→d Cabibbo-Kobayashi-Maskawa matrix element |Vcd| is determined to be ff0+(0)|Vcd|=0.0787±0.0060stat±0.0033syst for the first time. With the input of |Vcd| from the global fit in the standard model, we determine ff0+(0)=0.350±0.027stat±0.015syst. The absolute branching fractions of D+→f0(500)(π+π−)μ+νμ and D+→ρ0(π+π−)μ+νμ are determined as (0.72±0.13stat±0.10syst)×10−3 and (1.64±0.13stat±0.11syst)×10−3. Combining these results with those of previous BESIII measurements on their semielectronic counterparts from the same data sample, we test lepton flavor universality by measuring the branching fraction ratios BD+→ρ0μ+νμ/BD+→ρ0e+νe = 0.88±0.10 and BD+→f0(500)μ+νμ/BD+→f0(500)e+νe = 1.14±0.28, which are compatible with the standard model expectation.
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.
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.
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.
We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative decays of the J/ψ, using 10 billion J/ψ events collected with the BESIII detector. We find no evidence of a narrow resonance and set upper limits at the 95% confidence level on the product branching fraction B(J/ψ→γa)×B(a→γγ) and the axion-like particle photon coupling constant gaγγ in the ranges of (3.6−49.8)×10−8 and (2.2−103.8)×10−4 GeV−1, respectively, for 0.18≤ma≤2.85 GeV/c2. These are the most stringent limits to date in this mass region.
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.
A search has been performed for the semileptonic decays D0→K0SK−e+νe, D+→K0SK0Se+νe and D+→K+K−e+νe, using 7.9 fb−1 of e+e− annihilation data collected at the center-of-mass energy s√=3.773 GeV by the BESIII detector operating at the BEPCII collider. No significant signals are observed, and upper limits are set at the 90\% confidence level of 2.13×10−5, 1.54×10−5 and 2.10×10−5 for the branching fractions of D0→K0SK−e+νe, D+→K0SK0Se+νe and D+→K+K−e+νe, respectively.
Based on 4.5 fb−1 of e+e− collision data accumulated at center-of-mass energies between 4599.53 MeV and 4698.82 MeV with the BESIII detector, the decay Λ+c→nK0Sπ+π0 is observed for the first time with a significance of 9.2σ. The branching fraction is measured to be (0.85±0.13±0.03)%, where the first uncertainty is statistical and the second systematic, which differs from the theoretical prediction based on isospin by 4.4σ. This indicates that there may be resonant contributions or some unknown dynamics in this decay.
The process 𝑒+𝑒−→Σ+¯Σ− is studied from threshold up to 3.04 GeV/𝑐2 via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb−1, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of Σ are measured in eleven Σ+¯Σ− invariant mass intervals from threshold to 3.04 GeV/𝑐2. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays 𝐽/𝜓→Σ+¯Σ− and 𝜓(3686)→Σ+¯Σ− are determined and the obtained results are consistent with the previous results of BESIII.
The process e+e−→Σ+Σ¯− is studied from threshold up to 3.04 GeV/c2 via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb−1, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of Σ are measured in eleven Σ+Σ¯− invariant mass intervals from threshold to 3.04 GeV/c2. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays J/ψ→Σ+Σ¯− and ψ(3686)→Σ+Σ¯− are determined and the obtained results are consistent with the previous results of BESIII.
Using 7.33~fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies in the range of s√=4.128−4.226~GeV, we search for the rare decays D+s→h+(h0)e+e−, where h represents a kaon or pion. By requiring the e+e− invariant mass to be consistent with a ϕ(1020), 0.98<M(e+e−)<1.04 ~GeV/c2, the decay D+s→π+ϕ,ϕ→e+e− is observed with a statistical significance of 7.8σ, and evidence for the decay D+s→ρ+ϕ,ϕ→e+e− is found for the first time with a statistical significance of 4.4σ. The decay branching fractions are measured to be B(D+s→π+ϕ,ϕ→e+e−)=(1.17+0.23−0.21±0.03)×10−5, and B(D+s→ρ+ϕ,ϕ→e+e−)=(2.44+0.67−0.62±0.16)×10−5, where the first uncertainties are statistical and the second systematic. No significant signal for the three four-body decays of D+s→π+π0e+e−, D+s→K+π0e+e−, and D+s→K0Sπ+e+e− is observed. For D+s→π+π0e+e−, the ϕ mass region is vetoed to minimize the long-distance effects. The 90% confidence level upper limits set on the branching fractions of these decays are in the range of (7.0−8.1)×10−5.