Measurement of e+e− → ηJ/ψ cross section from √s= 3.808 GeV to 4.951 GeV

Using data samples with an integrated luminosity of 22.42  fb−1 collected by the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the +⁢−→⁢/ process at center-of-mass energies from 3.808 to 4.951 GeV. Three structures are observed in the line shape of the measured cross sections. A maximum-likelihood fit with ⁡(4040), two additional resonances, and a nonresonant component are performed. The mass and width of the first additional state are (4219.7±2.5±4.5)  MeV/2 and (80.7±4.4±1.4)  MeV, respectively, consistent with the ⁡(4230). For the second state, the mass and width are (4386±13±17)  MeV/2 and (177±32±13)  MeV, respectively, consistent with the ⁡(4360). The first uncertainties are statistical, and the second ones are systematic. The statistical significance of ⁡(4040) is 8.0⁢ and those for ⁡(4230) and ⁡(4360) are more than 10.0⁢

Measurement of the e+e− → K0SK0Lπ0 cross sections from √s = 2.000 to 3.080 GeV

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

Observation of the anomalous shape of X(1840) in J/ψ → γ3(π⁺π^(−)) indicating a second resonance near pp̄ threshold

Using a sample of (10087±44)×106  / events, which is about 45 times larger than that was previously analyzed, a further investigation on the /→⁢3⁢(+⁢−) decay is performed. A significant distortion at 1.84  GeV/2 in the line shape of the 3⁢(+⁢−) invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, ⁡(1840) and ⁡(1880). The new state ⁡(1880) is observed with a statistical significance larger than 10⁢. The mass and width of ⁡(1880) are determined to be 1882.1±1.7±0.7  MeV/2 and 30.7±5.5±2.4  MeV, respectively, which indicates the existence of a ⁢¯ bound state

Observation of the anomalous shape of X(1840) in J/ψ → γ3(π⁺π^(−)) indicating a second resonance Near pp̄ threshold

Using a sample of (10087±44)×106 J/ψ events, which is about 45 times larger than that was previously analyzed, a further investigation on the J/ψ→γ3(π+π−) decay is performed. A significant distortion at 1.84 GeV/c2 in the line-shape of the 3(π+π−) invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, X(1840) and X(1880). The new state X(1880) is observed with a statistical significance larger than 10σ. The mass and width of X(1880) are determined to be 1882.1±1.7±0.7 MeV/c2 and 30.7±5.5±2.4 MeV, respectively, which indicates the existence of a pp¯ bound state

Measurement of e⁺e^(−) → ωη´ cross sections at s√= 2.000 to 3.080 GeV

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

Measurement of e+e− → ηJ/ψ Cross Section from √s= 3.808 GeV to 4.951 GeV

Using data samples with an integrated luminosity of 22.42 fb−1 collected by the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the e^{+}e^{-}\rightarrow\etaJ/\psi process at center-of-mass energies from 3.808 to 4.951 GeV. Three structures are observed in the line shape of the measured cross sections. A maximum-likelihood fit with ψ(4040), two additional resonances, and a non-resonant component is performed. The mass and width of the first additional state are (4219.7±2.5±4.5)MeV/c2 and (80.7±4.4±1.4)MeV, respectively, consistent with the ψ(4230). For the second state, the mass and width are (4386±13±17)MeV/c2 and (177±32±13)MeV, respectively, consistent with the ψ(4360). The first uncertainties are statistical and the second ones are systematic. The statistical significance of ψ(4040) is 8.0σ and those for ψ(4230) and ψ(4360) are more than 10.0σ

Observation of the anomalous shape of X(1840) in J/ψ → γ3(π+π−)

Using a sample of (10087±44)×106 J/ψ events, which is about fifty times larger than that was previously analyzed, a further investigation on the J/ψ→γ3(π+π−) decay is performed. A significant distortion at 1.84 GeV/c2 in the line-shape of the 3(π+π−) invariant mass spectrum is observed for the first time, which is analogous to the behavior of X(1835) and could be resolved by two overlapping resonant structures, X(1840) and X(1880). The new state X(1880) is observed with a statistical significance of 14.7σ. The mass and width of X(1880) are determined to be 1882.1±1.7±0.7 MeV/c2 and 30.7±5.5±2.4 MeV, respectively, which indicates the existence of a pp¯ bound state

Evidence of the singly Cabibbo suppressed decay Λ+c → pπ0

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, which distinctly exceeds the upper limit measured by Belle experiment. 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, which is consistent with previous measurements

Search for the rare decays D_(s)⁺ → h⁺(h⁰)e⁺e^(−)

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

Observation of the helicity-selection-rule suppressed decay of the χ_(c2) charmonium state

The decays of χc2→K+K−π0, KSK±π∓ and π+π−π0 are studied with the ψ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of χc2→K∗K¯¯¯¯¯, χc2→a±2(1320)π∓/a02(1320)π0 and χc2→ρ(770)±π∓ are measured. Here K∗K¯¯¯¯¯ denotes both K∗±K∓ and K∗0K¯¯¯¯¯0+c.c., and K∗ denotes the resonances K∗(892), K∗2(1430) and K∗3(1780). The observations indicate a strong violation of the helicity selection rule in χc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of χc2→K∗(892)K¯¯¯¯¯ are more than 10 times larger than the upper limit of χc2→ρ(770)±π∓, which is so far the first direct observation of a significant U-spin symmetry breaking effect in charmonium decays