Observation of ηc (2S) →3 (π+π-) and measurements of χcJ →3 (π+π-) in ψ (3686) radiative transitions

The hadronic decay ηc(2S)→3(π+π-) is observed with a statistical significance of 9.3 standard deviations using (448.1±2.9)×106 ψ(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ηc(2S) are (3643.4±2.3 (stat)±4.4 (syst)) MeV/c2 and (19.8±3.9 (stat)±3.1 (syst)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[ψ(3686)→γηc(2S)]×B[ηc(2S)→3(π+π-)] is measured to be (9.2±1.0 (stat)±1.2 (syst))×10-6. Using B[ψ(3686)→γηc(2S)]=(7.0-2.5+3.4)×10-4, we obtain B[ηc(2S)→3(π+π-)]=(1.31±0.15 (stat)±0.17 (syst) (+0.64-0.47) (extr))×10-2, where the third uncertainty is from B[ψ(3686)→γηc(2S)]. We also measure the χcJ→3(π+π-) (J=0, 1, 2) decays via ψ′→γχcJ transitions. The branching fractions are B[χc0→3(π+π-)]=(2.080±0.006 (stat)±0.068 (syst))×10-2, B[χc1→3(π+π-)]=(1.092±0.004 (stat)±0.035 (syst))×10-2, and B[χc2→3(π+π-)]=(1.565±0.005 (stat)±0.048 (syst))×10-

Study of the Semileptonic Decay Λc+ → Λe+νe

The study of the Cabibbo-favored semileptonic decay Λc+→Λe+νe is reported using a 4.5 fb-1 data sample of e+e- annihilations collected at center-of-mass energies ranging from 4.600 GeV to 4.699 GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be B(Λc+→Λe+νe)=(3.56±0.11stat±0.07syst)%, which is the most precise measurement to date. Furthermore, we perform an investigation of the internal dynamics in Λc+→Λe+νe. We provide the first direct comparisons of the differential decay rate and form factors with those predicted from lattice quantum chromodynamics (LQCD) calculations. Combining the measured branching fraction with a q2-integrated rate predicted by LQCD, we determine |Vcs|=0.936±0.017B±0.024LQCD±0.007τΛ

Measurement of ψ (3686) → Λ Λ ¯ η and ψ (3686) → Λ Λ ¯ π0 decays

Based on a sample of 448.1 x 10(6) psi(3686) events collected with the BESIII detector, a study of psi(3686) -> Lambda(Lambda) over bar pi(0) and psi(3686) -> Lambda(Lambda) over bar eta is performed. Evidence of the isospin-violating decay psi(3686) -> Lambda(Lambda) over bar pi(0) is found for the first time with a statistical significance of 3.7 sigma, the branching fraction B(psi(3686) -> Lambda(Lambda) over bar pi(0)) is measured to be (1.42 +/- 0.39 +/- 0.59) x 10(-6), and its corresponding upper limit is determined to be 2.47 x 10(-6) at 90% confidence level. A partial wave analysis of psi(3686) -> Lambda(Lambda) over bar eta shows that the peak around Lambda eta invariant mass threshold favors a Lambda* resonance with mass and width in agreement with the Lambda(1670). The branching fraction of the psi(3686) -> Lambda(Lambda) over bar eta is measured to be (2.34 +/- 0.18 +/- 0.52) x 10(-5). The first uncertainties are statistical and the second are systematic

Observation of Ξ- Hyperon transverse polarization in ψ (3686) → Ξ-Ξ¯

Using a sample of (448.1±2.9)×106 ψ(3686) decays collected with the BESIII detector at BEPCII, we report an observation of Ξ- transverse polarization with a significance of 7.3σ in the decay ψ(3686)→Ξ-Ξ¯+ (Ξ-→Λπ-, Ξ¯+→Λ¯π+, Λ→pπ-, Λ¯→p¯π+). The relative phase of the electric and magnetic form factors is determined to be Δφ=(0.667±0.111±0.058) rad. This is the first measurement of the relative phase for a ψ(3686) decay into a pair of Ξ-Ξ¯+ hyperons. The Ξ- decay parameters (αΞ-, φΞ-) and their conjugates (αΞ¯+, φΞ¯+), the angular-distribution parameter αψ, and the strong-phase difference δp-δs for Λπ- scattering are measured to be consistent with previous BESIII result