Study of e+e−→2(pp¯) at center-of-mass energies between 4.0 and 4.6 GeV

Using data taken at 23 center-of-mass energies between 4.0 and 4.6 GeV with the BESIII detector at the Beijing Electron Positron Collider and with a total integrated luminosity of approximately 15 fb-1, the process e+e-→2(pp¯) is studied for the first time. The Born cross sections for e+e-→2(pp¯) are measured, and no significant structure is observed in the lineshape. The baryon pair (pp and p¯p¯) invariant mass spectra are consistent with phase space, therefore no hexaquark or di-baryon state is found

Observation of a Near-Threshold Structure in the K+ Recoil-Mass Spectra in e+⁢e−→K+⁢(D−s⁢D*0+D*− s⁢D0)

We report a study of the processes of e+⁢e− →K+⁢D− s⁢D*0 and K+⁢D*−s⁢D0 based on e+⁢e− annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb−1. An excess of events over the known contributions of the conventional charmed mesons is observed near the D−s⁢D*0 and D*−s⁢D0 mass thresholds in the K+ recoil-mass spectrum for events collected at √s =4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5+1.8 −2.6±2.1) MeV/c2 and (12.8+5.3 −4.4 ±3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 σ over the contributions only from the conventional charmed mesons. This is the first candidate for a charged hidden-charm tetraquark with strangeness, decaying into D− s⁢D*0 and D*− s⁢D0. However, the properties of the excess need further exploration with more statistics

Amplitude analysis and branching fraction measurement of the decay Ds+→π+π0π0D_{s}^{+} \to \pi^{+}\pi^{0}\pi^{0}

Using a data set corresponding to an integrated luminosity of 6.32~$\rm fb^{-1}$ recorded by the BESIII detector at center-of-mass energies between 4.178 and 4.226~GeV, an amplitude analysis of the decay $D_{s}^{+} \to \pi^{+}\pi^{0}\pi^{0}$ is performed, and the relative fractions and phases of different intermediate processes are determined. The absolute branching fraction of the decay $D_{s}^{+} \to \pi^{+}\pi^{0}\pi^{0}$ is measured to be $(0.50\pm 0.04_{\text{stat}}\pm 0.02_{\text{syst}})\%$. The absolute branching fraction of the intermediate process $D_{s}^{+} \to f_0(980)\pi^{+}, f_0(980)\to\pi^{0}\pi^{0}$ is determined to be $(0.21\pm 0.03_{\text{stat}}\pm 0.03_{\text{syst}})\%$

Amplitude analysis and branching fraction measurement of Ds+→K−K+π+π0

The first amplitude analysis of the decay Ds+→K-K+π+π0 is presented using the data samples, corresponding to an integrated luminosity of 6.32 fb-1, collected with the BESIII detector at e+e- center-of-mass energies between 4.178 and 4.226 GeV. More than 3000 events selected with a purity of 97.5% are used to perform the amplitude analysis, and nine components are found necessary to describe the data. Relative fractions and phases of the intermediate decays are determined. With the detection efficiency estimated by the results of the amplitude analysis, the branching fraction of Ds+→K-K+π+π0 decay is measured to be (5.42±0.10stat±0.17syst)

Search for the lepton number violating decay Σ−→pe−e− and the rare inclusive decay Σ−→Σ+X

Using a data sample of (1310.6±7.0)×106 J/ψ events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay ς-→pe-e- and the rare inclusive decay ς-→ς+X, where X denotes any possible particle combination. The ς- candidates are tagged in J/ψ→ς¯(1385)+ς- decays. No signal candidates are found, and the upper limits on the branching fractions at the 90% confidence level are determined to be B(ς-→pe-e-)<6.7×10-5 and B(ς-→ς+X)<1.2×10-4

Measurement of the doubly Cabibbo-suppressed decay D+→K+π+π−π0 with semileptonic tags

We propose a new semileptonic tag method to study the doubly Cabibbo-suppressed D decay in ψ(3770)→DD¯ reaction. Utilizing the dataset corresponding to an integrated luminosity of 2.93 fb-1 at a center-of-mass energy of 3.773 GeV collected by the BESIII detector, we determine the branching fraction for D+→K+π+π-π0 to be (1.03±0.12stat±0.06syst)×10-3, in which the contributions from narrow intermediate resonances, D+→K+η, D+→K+ω, and D+→K+φ have been excluded. Combining the world average of the branching fraction of D+→K-π+π+π0, we determine B(D+→K+π+π-π0)/B(D+→K-π+π+π0)=(1.65±0.21)%, corresponding to (5.73±0.73)tan4θc, where θc is the Cabibbo mixing angle. These results are consistent with our previous measurement with hadronic tags but are significantly larger than other doubly Cabibbo-suppressed decays in the charm sector