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Institute
Using 15.6 fb−1 of e+e− collision data collected at twenty-four center-of-mass energies from 4.0 to 4.6 GeV with the BESIII detector, the helicity amplitudes of the process e+e−→π+π−ω are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5σ are presented, such as f0(500), f0(980), f2(1270), f0(1370), b1(1235)±, and ρ(1450)±. In addition, evidence of a resonance state in e+e−→π+π−ω production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/c2, which is consistent with the production of ψ(4160) or Y(4220).
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.
Based on (10087±44)×106 J/ψ events collected with the BESIII detector, the process J/ψ→γπ+π−η′ is studied using two dominant decay channels of the η′ meson, η′→γπ+π− and η′→ηπ+π−,η→γγ. The X(2600) is observed with a statistical significance larger than 20σ in the π+π−η′ invariant mass spectrum, and it has a strong correlation to a structure around 1.5 GeV/{\it c}2 in the π+π− invariant mass spectrum. A simultaneous fit on the π+π−η′ and π+π− invariant mass spectra with the two η′ decay modes indicates that the mass and width of the X(2600) state are 2617.8±2.1+18.2−1.9 MeV/{\it c}2 and 200±8+20−17 MeV, respectively. The corresponding branching fractions are measured to be B(J/ψ→γX(2600))⋅B(X(2600)→f0(1500)η′)⋅B(f0(1500)→π+π−) = (3.39±0.18+0.91−0.66)×10−5 and B(J/ψ→γX(2600))⋅B(X(2600)→f′2(1525)η′)⋅B(f′2(1525)→π+π−) = (2.43±0.13+0.31−1.11)×10−5, where the first uncertainties are statistical, and the second systematic.
Using 448 million ψ(2S) events, the spin-singlet P-wave charmonium state hc(11P1) is studied via the ψ(2S)→π0hc decay followed by the hc→γηc transition. The branching fractions are measured to be BInc(ψ(2S)→π0hc)×BTag(hc→γηc)=(4.22+0.27−0.26±0.19)×10−4 , BInc(ψ(2S)→π0hc)=(7.32±0.34±0.41)×10−4, and BTag(hc→γηc)=(57.66+3.62−3.50±0.58)%, where the uncertainties are statistical and systematic, respectively. The hc(11P1) mass and width are determined to be M=(3525.32±0.06±0.15) MeV/c2 and Γ=(0.78+0.27−0.24±0.12) MeV. Using the center of gravity mass of the three χcJ(13PJ) mesons (M(c.o.g.)), the 1P hyperfine mass splitting is estimated to be Δhyp=M(hc)−M(c.o.g.)=(0.03±0.06±0.15) MeV/c2, which is consistent with the expectation that the 1P hyperfine splitting is zero at the lowest-order.
Analyzing (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the ψ(3686)→ωK0SK0S decay is observed for the first time. The branching fraction for this decay is determined to be Bψ(3686)→ωK0SK0S=(7.04±0.39±0.36)×10−5, where the first uncertainty is statistical and the second is systematic.
Based on a sample of (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/ψ→γηη′ is performed. An isoscalar state with exotic quantum numbers JPC=1−+, denoted as η1(1855), has been observed for the first time with statistical significance larger than 19σ. Its mass and width are measured to be (1855±9+6−1)~MeV/c2 and (188±18+3−8)~MeV, respectively. The product branching fraction B(J/ψ→γη1(1855)→γηη′) is measured to be (2.70±0.41+0.16−0.35)×10−6. The first uncertainties are statistical and the second are systematic. In addition, an upper limit on the branching ratio B(f0(1710)→ηη′)/B(f0(1710)→ππ) is determined to be 1.61×10−3 at 90\% confidence level, which lends support to the hypothesis that the f0(1710) has a large glueball component.
By analyzing an electron-positron collision data sample corresponding to an integrated luminosity of 2.93 fb−1 taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, we obtain for the first time the absolute branching fractions for seven 𝐷0 and 𝐷+ hadronic decay modes and search for the hadronic decay 𝐷0→𝐾0𝑆𝐾0𝑆𝜋0 with much improved sensitivity. The results are ℬ(𝐷0→𝐾0𝑆𝜋0𝜋0𝜋0)=(7.64±0.30±0.29)×10−3, (𝐷0→𝐾−𝜋+𝜋0𝜋0𝜋0)=9.54±0.30±0.31)×10−3, ℬ(𝐷0→𝐾0𝑆𝜋+𝜋−𝜋0𝜋0)=(12.66±0.45±0.43)×10−3, ℬ(𝐷+→𝐾0𝑆𝜋+𝜋0𝜋0)=(29.04±0.62±0.87)×10−3, ℬ(𝐷+→𝐾0𝑆𝜋+𝜋+𝜋−𝜋0)=(15.28±0.57±0.60)×10−3, ℬ(𝐷+→𝐾0𝑆𝜋+𝜋0𝜋0𝜋0)=(5.54±0.44±0.32)×10−3, ℬ(𝐷+→𝐾−𝜋+𝜋+𝜋0𝜋0)=(4.95±0.26±0.19)×10−3, and ℬ(𝐷0→𝐾0𝑆𝐾0𝑆𝜋0)<1.45×10−4 at the 90% confidence level. Here, the first uncertainties are statistical, and the second ones are systematic. The newly studied decays greatly enrich the knowledge of the 𝐷→¯𝐾𝜋𝜋𝜋 and 𝐷→¯𝐾𝜋𝜋𝜋𝜋 hadronic decays and open a bridge to access more two-body hadronic 𝐷 decays containing scalar, vector, axial, and tensor mesons in the charm sector.
We present the first experimental search for the rare charm decay D0→π0ν¯ν. It is based on an e+e− collision sample consisting of 10.6×10^6 pairs of D0¯D0 mesons collected by the BESIII detector at √s=3.773 GeV, corresponding to an integrated luminosity of 2.93 fb^−1. A data-driven method is used to ensure the reliability of the background modeling. No significant D0→π0ν¯ν signal is observed in data and an upper limit of the branching fraction is set to be 2.1×10^-4 at the 90% confidence level. This is the first experimental constraint on charmed-hadron decays into dineutrino final states.
Using an 𝑒+𝑒− collision data sample of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of 𝐷0→𝑎0(980)−𝑒+𝜈𝑒 and evidence for 𝐷+→𝑎0(980)0𝑒+𝜈𝑒 with significances of 6.4𝜎 and 2.9𝜎, respectively. The absolute branching fractions are determined to be ℬ(𝐷0→𝑎0(980)−𝑒+𝜈𝑒)×ℬ(𝑎0(980)−→𝜂𝜋−) = [1.33+0.33−0.29(stat)±0.09(syst)]×10−4 and ℬ(𝐷+→𝑎0(980)0𝑒+𝜈𝑒)×ℬ(𝑎0(980)0→𝜂𝜋0)=[1.66+0.81
−0.66(stat)±0.11(syst)]×10−4. This is the first time the 𝑎0(980) meson has been measured in a 𝐷0 semileptonic decay, which would open one more interesting page in the investigation of the nature of the puzzling 𝑎0(980) states.
Using 𝑒+𝑒−→Λ+𝑐¯Λ−𝑐 production from a 567 pb−1 data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried out simultaneously on the four decay modes of Λ+𝑐→𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0, and Σ0𝜋+. For the first time, the Λ+𝑐 transverse polarization is studied in unpolarized 𝑒+𝑒− collisions, where a nonzero effect is observed with a statistical significance of 2.1𝜎. The decay asymmetry parameters of the Λ+𝑐 weak hadronic decays into 𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0 and Σ0𝜋+ are measured to be 0.18±0.43(stat)±0.14(syst), −0.80±0.11(stat)±0.02(syst), −0.57±0.10(stat)±0.07(syst), and −0.73±0.17(stat)±0.07(syst), respectively. In comparison with previous results, the measurements for the Λ𝜋+ and Σ+𝜋0 modes are consistent but with improved precision, while the parameters for the 𝑝𝐾0𝑆 and Σ0𝜋+ modes are measured for the first time.