Measurement of np->npπ0π0 reaction in search for the recently observed d*(2380) resonance

Exclusive measurements of the quasi-free np →npπ0π0reaction have been performed by means of dpcollisions at Td=2.27GeVusing the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region √s=(2.35–2.46)GeV, which includes the region of the ABC effect and its associated d∗(2380)resonance. Adding the d∗resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Fäldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e.the low-mass enhancement in the π0π0-invariant mass spectrum, is found to be very modest – if present at all, which might pose a problem to some of its interpretations

Amplitude analysis and branching-fraction measurement of Ds+ → π + π 0 η′

Using data collected with the BESIII detector in e+e− collisions at center-of-mass energies between 4.178 and 4.226 GeV and corresponding to 6.32 fb−1 of integrated luminosity, we report the amplitude analysis and branching-fraction measurement of the Ds+→ π+π0η′ decay. We find that the dominant intermediate process is Ds+→ ρ+η′ and the significances of other resonant and nonresonant processes are all less than 3σ. The upper limits on the branching fractions of S-wave and P-wave nonresonant components are set to 0.10% and 0.74% at the 90% confidence level, respectively. In addition, the branching fraction of the Ds+→ π+π0η′ decay is measured to be (6.15 ± 0.25(stat.) ± 0.18(syst.))%, which receives significant contribution only from Ds+→ ρ+η′ according to the amplitude analysis. [Figure not available: see fulltext.]. © 2022, The Author(s)

Search for a CP-odd light Higgs boson in J/ψ →γA⁰

Using J/ψ radiative decays from 9.0 billion J/ψ events collected by the BESIII detector, we search for di-muon decays of a CP-odd light Higgs boson (A0), predicted by many new physics models beyond the Standard Model, including the next-to-minimal supersymmetric Standard Model. No evidence for the CP-odd light Higgs production is found, and we set 90% confidence level upper limits on the product branching fraction B(J/ψ→γA0)×B(A0→μ+μ-) in the range of (1.2-778.0)×10-9 for 0.212≤mA0≤3.0 GeV/c2. The new measurement is a 6-7 times improvement over our previous measurement, and is also slightly better than the BABAR measurement in the low-mass region for tanβ=1

Oscillating features in the electromagnetic structure of the neutron

The complicated structure of the neutron cannot be calculated using first-principles calculations due to the large colour charge of quarks and the self-interaction of gluons. Its simplest structure observables are the electromagnetic form factors1, which probe our understanding of the strong interaction. Until now, a small amount of data has been available for the determination of the neutron structure from the time-like kinematical range. Here we present measurements of the Born cross section of electron–positron annihilation reactions into a neutron and anti-neutron pair, and determine the neutron’s effective form factor. The data were recorded with the BESIII experiment at centre-of-mass energies between 2.00 and 3.08 GeV using an integrated luminosity of 647.9 pb−1. Our results improve the statistics on the neutron form factor by more than a factor of 60 over previous measurements, demonstrating that the neutron form factor data from annihilation in the time-like regime is on par with that from electron scattering experiments. The effective form factor of the neutron shows a periodic behaviour, similar to earlier observations of the proton form factor. Future works—both theoretical and experimental—will help illuminate the origin of this oscillation of the electromagnetic structure observables of the nucleon

Measurement of the branching fraction of leptonic decay D⁺_s → τ⁺ν_τ via τ⁺→ π⁺π⁰¯ν_τ

By analyzing 6.32  fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay D+s→τ+ντ, with τ+→π+π0¯ντ, to be BD+s→τ+ντ=(5.29±0.25stat±0.20syst)%. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element |Vcs| and the D+s decay constant fD+s to be fD+s|Vcs|=(244.8±5.8stat±4.8syst)  MeV, using the known values of the τ+ and D+s masses as well as the D+s lifetime, together with our branching fraction measurement. Combining the value of |Vcs| obtained from a global fit in the standard model and fD+s from lattice quantum chromodynamics, we obtain fD+s=(251.6±5.9stat±4.9syst)  MeV and |Vcs|=0.980±0.023stat±0.019syst. Using the branching fraction of BD+s→μ+νμ=(5.35±0.21)×10−3, we obtain the ratio of the branching fractions BD+s→τ+ντ/BD+s→μ+νμ=9.89±0.71, which is consistent with the standard model prediction of lepton flavor universality

Partial wave analysis of ψ(3686) → K⁺K⁻η

Using a sample of (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector, we perform the first partial wave analysis of ψ(3686)→K+K-η. In addition to the well established states, φ(1020), φ(1680), and K3∗(1780), contributions from X(1750), ρ(2150), ρ3(2250), and K2∗(1980) are also observed. The X(1750) state is determined to be a 1-resonance. The simultaneous observation of the φ(1680) and X(1750) indicates that the X(1750), with previous observations in photoproduction, is distinct from the φ(1680). The masses, widths, branching fractions of ψ(3686)→K+K-η, and the intermediate resonances are also measured

Observation of ψ(3686) → Ξ(1530)⁰Ξ¯(1530)⁰ and Ξ(1530)⁰Ξ¯⁰

Using (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector and a single-baryon tagging technique, we present the first observation of the decays ψ(3686)→Ξ(1530)0Ξ¯(1530)0 and Ξ(1530)0Ξ¯0. The branching fractions are measured to be B(ψ(3686)→Ξ(1530)0Ξ¯(1530)0)=(6.77±0.14±0.39)×10-5 and B(ψ(3686)→Ξ(1530)0Ξ¯0)=(0.53±0.04±0.03)×10-5. Here, the first and second uncertainties are statistical and systematic, respectively. In addition, the parameter associated with the angular distribution for the decay ψ(3686)→Ξ(1530)0Ξ¯(1530)0 is determined to be α=0.32±0.19±0.07, in agreement with theoretical predictions within one standard deviation

Study of the process <i>e⁺e⁻ </i>→ π⁰π⁰<i>J/ψ</i> and neutral charmoniumlike state <i>Z_c</i>(3900)⁰

Cross sections of the process e+e−→π0π0J/ψ at center-of-mass energies between 3.808 and 4.600 GeV are measured with high precision by using 12.4  fb−1 of data samples collected with the BESIII detector operating at the BEPCII collider facility. A fit to the measured energy-dependent cross sections confirms the existence of the charmoniumlike state Y(4220). The mass and width of the Y(4220) are determined to be (4220.4±2.4±2.3) MeV/c2 and (46.2±4.7±2.1)  MeV, respectively, where the first uncertainties are statistical and the second systematic. The mass and width are consistent with those measured in the process e+e−→π+π−J/ψ. The neutral charmonium-like state Zc(3900)0 is observed prominently in the π0J/ψ invariant-mass spectrum, and, for the first time, an amplitude analysis is performed to study its properties. The spin-parity of Zc(3900)0 is determined to be JP=1+, and the pole position is (3893.1±2.2±3.0)−i(22.2±2.6±7.0)  MeV/c2, which is consistent with previous studies of electrically charged Zc(3900)±. In addition, cross sections of e+e−→π0Zc(3900)0→π0π0J/ψ are extracted, and the corresponding line shape is found to agree with that of the Y(4220)

Search for the hyperon semileptonic decay Ξ⁻→Ξ⁰e⁻¯¯¯ν_e

Using (10.087±0.044)×109  J/ψ events collected by the Beijing Spectrum III (BESIII) detector at the Beijing Electron Positron Collider II (BEPCII) collider, we search for the hyperon semileptonic decay Ξ−→Ξ0e−¯νe. No significant signal is observed and the upper limit on the branching fraction B(Ξ−→Ξ0e−¯νe) is set to be 2.59×10−4 at 90% confidence level. This result is one order of magnitude more strict than the previous best limit