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Institute
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Using data samples with an integrated luminosity of 19 fb−1 at twenty-eight center-of-mass energies from 3.872 GeV to 4.700 GeV collected with the BESIII detector at the BEPCII electron-positron collider, the process e+e− → ηπ+π− and the intermediate process e+e− → ηρ0 are studied for the first time. The Born cross sections are measured. No significant resonance structure is observed in the cross section lineshape.
The Born cross section of the process e+e−→ηJ/ψ at a center-of-mass energy s√=3.773 GeV is measured to be (8.89±0.88±0.42) pb, using a data sample collected with the BESIII detector operating at the BEPCII storage ring. The decay ψ(3770)→ηJ/ψ is observed for the first time with a statistical significance of 7.4σ. From a fit to the dressed cross-section line-shape of e+e−→ηJ/ψ from s√=3.773 to 4.600 GeV we obtain the branching fraction of the decay ψ(3770)→ηJ/ψ to be (11.6±6.1±1.0)×10−4 when the ψ(3770) decay amplitude is added coherently to the other contributions, and (7.9±1.0±0.7)×10−4 when it is added incoherently. Here the first uncertainties are statistical and the second are systematic.
Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, the Born cross section of the process 𝑒+𝑒−→𝜂𝐽/𝜓 at a center-of-mass energy √𝑠=3.773 GeV is measured to be (8.88±0.87±0.42) pb. We fit the cross section line shape before correcting for the initial state radiation from √𝑠=3.773 to 4.600 GeV to obtain the branching fraction ℬ(𝜓(3770)→𝜂𝐽/𝜓). We obtain ℬ(𝜓(3770)→𝜂𝐽/𝜓)=(11.3±5.9±1.1)×10−4 when the 𝜓(3770) decay amplitude is added coherently to the other contributions, and (8.7±1.0±0.8)×10−4 when it is added incoherently. Here the quoted uncertainties are statistical and systematic, respectively. In both cases, the statistical significance of 𝜓(3770) resonance is above 7𝜎. This is the first time the decay 𝜓(3770)→𝜂𝐽/𝜓 is observed with a statistical significance greater than 5𝜎.
The Cabibbo-allowed weak radiative decay Λ+c→Σ+γ has been searched for in a sample of Λ+cΛ¯−c pairs produced in e+e− annihilations, corresponding to an integrated luminosity of 4.5fb−1 collected with the BESIII detector at center-of-mass energies between 4.60 and 4.70 GeV. No excess of signal above background is observed, and we set an upper limit on the branching fraction of this decay to be B(Λ+c→Σ+γ)<4.4×10−4 at a confidence level of 90\%, which is in agreement with Standard Model expectations.
The Cabibbo-allowed weak radiative decay Λ+c→Σ+γ has been searched for in a sample of Λ+cΛ¯−c pairs produced in e+e− annihilations, corresponding to an integrated luminosity of 4.5fb−1 collected with the BESIII detector at center-of-mass energies between 4.60 and 4.70 GeV. No excess of signal above background is observed, and we set an upper limit on the branching fraction of this decay to be B(Λ+c→Σ+γ)<4.4×10−4 at a confidence level of 90\%, which is in agreement with Standard Model expectations.
We report a search for a heavier partner of the recently observed Zcs(3985)− state, denoted as Z′−cs, in the process e+e−→K+D∗−sD∗0+c.c., based on e+e− collision data collected at the center-of-mass energies of s√=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Z′−cs is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate K+ recoil-mass spectra, which are probed for a potential contribution from Z′−cs→D∗−sD∗0 (c.c.). We find an excess of Z′−cs→D∗−sD∗0 (c.c.) candidates with a significance of 2.1σ, after considering systematic uncertainties, at a mass of (4123.5±0.7stat.±4.7syst.) MeV/c2. As the data set is limited in size, the upper limits are evaluated at the 90\% confidence level on the product of the Born cross sections (σBorn) and the branching fraction (B) of Z′−cs→D∗−sD∗0, under different assumptions of the Z′−cs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of σBorn⋅B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Z′−cs state and clarify its nature in the coming years.
We report a search for a heavier partner of the recently observed Zcs(3985)− state, denoted as Z′−cs, in the process e+e−→K+D∗−sD∗0+c.c., based on e+e− collision data collected at the center-of-mass energies of s√=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Z′−cs is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate K+ recoil-mass spectra, which are probed for a potential contribution from Z′−cs→D∗−sD∗0 (c.c.). We find an excess of Z′−cs→D∗−sD∗0 (c.c.) candidates with a significance of 2.1σ, after considering systematic uncertainties, at a mass of (4123.5±0.7stat.±4.7syst.) MeV/c2. As the data set is limited in size, the upper limits are evaluated at the 90\% confidence level on the product of the Born cross sections (σBorn) and the branching fraction (B) of Z′−cs→D∗−sD∗0, under different assumptions of the Z′−cs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of σBorn⋅B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Z′−cs state and clarify its nature in the coming years.
We measure the inclusive semielectronic decay branching fraction of the D+s meson. A double-tag technique is applied to e+e− annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range 4.178–4.230 GeV. We select positrons fromD+s→Xe+νe with momenta greater than 200 MeV/c and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the D+s semielectronic branching fraction to be(6.30±0.13(stat.)±0.09(syst.)±0.04(ext.))%, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the D+s and D0 semielectronic widths, Γ(D+s→Xe+νe)Γ(D0→Xe+νe)=0.790±0.016(stat.)±0.011(syst.)±0.016(ext.). Our results are consistent with and more precise than previous measurements.
The integrated luminosities of data samples collected in the BESIII experiment in 2016–2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010–2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur.
Search for the reaction channel e⁺e⁻ → ηcηπ⁺π⁻ at center-of-mass energies from 4.23 to 4.60 GeV
(2021)
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process 𝑒+𝑒−→𝜂𝑐𝜂𝜋+𝜋−. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The 𝜂𝑐 meson is reconstructed in 16 exclusive decay modes. No signal is observed in the 𝜂𝑐 mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.