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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.
The Cabbibo-favored decay Λ+c→Ξ0K+π0 is studied for the first time using 6.1 fb−1 of e+e− collision data at center-of-mass energies between 4.600 and 4.840 GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay Λ+c→Ξ0K+π0 is measured to be (7.79±1.46±0.71)×10−3, where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay Λ+c→Ξ(1530)0K+ is (5.99±1.04±0.29)×10−3, which is consistent with the previous result of (5.02±0.99±0.31)×10−3. In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay Λ+c→nK+π0 is 7.1×10−4 at the 90% confidence level. The upper limits on the branching fractions of Λ+c→Σ0K+π0 and ΛK+π0 are also determined to be 1.8×10−3 and 2.0×10−3, respectively.
The Cabbibo-favored decay Λ+c→Ξ0K+π0 is studied for the first time using 6.1 fb−1 of e+e− collision data at center-of-mass energies between 4.600 and 4.840 GeV, collected with the BESIII detector at the BEPCII collider. With a double-tag method, the branching fraction of the three-body decay Λ+c→Ξ0K+π0 is measured to be (7.79±1.46±0.71)×10−3, where the first and second uncertainties are statistical and systematic, respectively. The branching fraction of the two-body decay Λ+c→Ξ(1530)0K+ is (5.99±1.04±0.29)×10−3, which is consistent with the previous result of (5.02±0.99±0.31)×10−3. In addition, the upper limit on the branching fraction of the doubly Cabbibo-suppressed decay Λ+c→nK+π0 is 7.1×10−4 at the 90% confidence level. The upper limits on the branching fractions of Λ+c→Σ0K+π0 and ΛK+π0 are also determined to be 1.8×10−3 and 2.0×10−3, respectively.
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.
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−→𝜂𝐽/𝜓 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 nonresonant component are 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.
Using (1.0087±0.0044)×1010 𝐽/𝜓 events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays Ξ0→𝐾−𝑒+ with Δ(𝐵−𝐿)=0 and Ξ0→𝐾+𝑒− with |Δ(𝐵−𝐿)|=2, where 𝐵 (𝐿) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to ℬ(Ξ0→𝐾−𝑒+)<3.6×10−6 and ℬ(Ξ0→𝐾+𝑒−)<1.9×10−6 at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.
Using a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy s√=3.773 GeV by the BESIII detector, the decay D0→ωϕ is observed for the first time. The branching fraction is measured to be (6.48±0.96±0.40)×10−4 with a significance of 6.3σ, where the first and second uncertainties are statistical and systematic, respectively. An angular analysis reveals that the ϕ and ω mesons from the D0→ωϕ decay are transversely polarized. The 95% confidence level upper limit on longitudinal polarization fraction is set to be less than 0.24, which is inconsistent with current theoretical expectations and challenges our understanding of the underlying dynamics in charm meson decays.
Using data samples with a total integrated luminosity of 20.1 fb−1 collected by the BESIII detector operating at the BEPCII collider, the cross section of the process 𝑒+𝑒−→𝜋+𝜋−𝜓(3686) is measured at center-of-mass energies between 4.0076 and 4.6984 GeV. The measured cross section is consistent with previous results, and with much improved precision. A fit to the measured energy-dependent cross section, which includes three Breit-Wigner functions and a nonresonant contribution, confirms the existence of the charmonium-like states 𝑌(4220), 𝑌(4390), and 𝑌(4660). This is the first observation of the 𝑌(4660) at the BESIII experiment.
Using inclusive decays of the J/ψ, a precise determination of the number of J/ψ events collected with the BESIII detector is performed. For the two data sets taken in 2009 and 2012, the numbers of J/ψ events are recalculated to be (224.0±1.3)×106 and (1088.5±4.4)×106 respectively, which are in good agreement with the previous measurements. For the J/ψ sample taken in 2017--2019, the number of events is determined to be (8774.0±39.4)×106. The total number of J/ψ events collected with the BESIII detector is determined to be (10087±44)×106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, the cross section of the inclusive process e+e−→η+X, normalized by the total cross section of e+e−→hadrons, is measured at eight center-of-mass energy points from 2.0000 GeV to 3.6710 GeV. These are the first measurements with momentum dependence in this energy region. Our measurement shows a significant discrepancy from calculations with the existing fragmentation functions. To address this discrepancy, a new QCD analysis is performed at the next-to-next-to-leading order with hadron mass corrections and higher twist effects, which can explain both the established high-energy data and our measurements reasonably well.