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We search for the semi-leptonic decays Λ + c → Λπ+π−e+νe and Λ + c → pK0 Sπ−e+νe in a sample of 4.5 fb−1 of e+e− annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Λ+c → Λπ+π−e+νe ) < 3.9 × 10−4 and B(Λ + c → pK0Sπ−e+νe ) < 3.3 × 10−4 at the 90% confidence level, respectively.
Based on 4.5 fb−1 data taken at seven center-of-mass energies ranging from 4.600 to 4.699 GeV with the BESIII detector at the BEPCII collider, we measure the branching fractions of Λ + c → Σ + + hadrons relative to Λ + c → Σ +π +π −. Combining with the world average branching fraction of Λ + c → Σ +π +π −, their branching fractions are measured to be (0.377 ± 0.042 ± 0.020 ± 0.021)% for Λ + c → Σ +K+K−, (0.200 ± 0.023 ± 0.011 ± 0.011)% for Λ + c → Σ+K+π−, (0.414 ± 0.080 ± 0.030 ± 0.023)% for Λ + c → Σ +φ and (0.197 ± 0.036 ± 0.009 ± 0.011)% for Λ + c → Σ +K+K−(non-φ). In all the above results, the first uncertainties are statistical, the second are systematic and the third are from external input of the branching fraction of Λ + c → Σ +π +π −. Since no signal for Λ + c → Σ +K+π−π 0 is observed, the upper limit of its branching fraction is determined to be 0.13% at the 90% confidence level.
With data samples collected with the BESIII detector at seven energy points at √s = 3.68 − 3.71 GeV, corresponding to an integrated luminosity of 333 pb−1, we present a study of the Λ transverse polarization in the e+e− → ΛΛ¯ reaction. The signifcance of polarization by combining the seven energy points is found to be 2.6σ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the ΛΛ¯ helicity states. The modulus ratio and the relative phase of EM-psionic form factors combined with all energy points are measured to be RΨ = 0.71+0.10−0.10 ± 0.03 and ∆ΦΨ = 23+8.8−8.0 ± 1.6◦, where the frst uncertainties are statistical and the second systematic.
The cross sections of the 𝑒+𝑒−→𝜙𝜂′ process at center-of-mass energies from 3.508 to 4.951 GeV are measured with high precision using 26.1 fb−1 data collected with the BESIII detector operating at the BEPCII storage ring. The cross sections are of the order of a few picobarn and decrease as the center-of-mass energy increases as 𝑠−𝑛/2 with 𝑛=4.35±0.14. This result is in agreement with the Nambu-Jona-Lasinio model prediction of 𝑛=3.5±0.9. In addition, the charmless decay 𝜓(3770)→𝜙𝜂′ is searched for by fitting the measured cross sections, yet no significant signal is observed. The upper limit of ℬ(𝜓(3770)→𝜙𝜂′) at the 90% confidence level is determined to be 2.3×10−5.
Using 4.5fb−1 of e+e− annihilation data samples collected at center-of-mass energies ranging from 4.600 to 4.698 GeV with the BESIII detector at the BEPCII collider, we measured the absolute branching fraction for the inclusive semileptonic decay Λ+c→Xe+νe, where X refers to any possible particle system. The branching fraction of the decay is determined to be B(Λ+c→Xe+νe)=(4.06±0.10stat.±0.09syst.)%. Our result improves the precision of previous measurement of B(Λ+c→Xe+νe) by more than threefold. Using the known Λ+c lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons, we measure the ratio of inclusive semileptonic decay widths Γ(Λ+c→Xe+νe)/Γ¯(D→Xe+νe)=1.28±0.05, where statistical and systematic uncertainties are combined.
Based on 4.4 fb−1 of e+e− annihilation data collected at the center-of-mass energies between 4.60 and 4.70 GeV with the BESIII detector at the BEPCII collider, the pure \textit{W}-boson-exchange decay Λ+c→Ξ0K+ is studied with a full angular analysis. The corresponding decay asymmetry is measured for the first time to be αΞ0K+=0.01±0.16(stat.)±0.03(syst.). This result reflects the non-interference effect between the S- and P-wave amplitudes. The phase shift between S- and P-wave amplitudes has two solutions, which are δp−δs=−1.55±0.25(stat.)±0.05(syst.) rad or 1.59±0.25(stat.)±0.05(syst.) rad.
Using a data sample of (10087±44)×106 J/ψ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process J/ψ→e+e−η(1405) is observed via the decay η(1405)→π0f0(980), f0(980)→π+π−, with a significance of about 9.6σ. The branching fraction of this decay is measured to be B(J/ψ→e+e−π0η(1405)→e+e−π0f0(980)→e+e−π0π+π−)=(2.02±0.24(stat.)±0.09(syst.))×10−7. The branching-fraction ratio B(J/ψ→e+e−η(1405))/B(J/ψ→γη(1405)) is determined to be (1.35±0.19(stat.)±0.06(syst.))×10−2. Furthermore, an e+e− invariant-mass dependent transition form factor of J/ψ→e+e−η(1405) is presented for the first time. The obtained result provides input for different theoretical models, and is valuable for the improved understanding the intrinsic structure of the η(1405) meson.
Based on data samples collected with the BESIII detector at the BEPCII collider, the process e+e−→Σ+Σ¯− is studied at center-of-mass energies s√ = 2.3960, 2.6454, and 2.9000~GeV. Using a fully differential angular description of the final state particles, the complete information of the Σ+ electromagnetic form factors in the time-like region is extracted. The relative phase between the electric and magnetic form factors is determined to be sinΔΦ = -0.67~±~0.29~(stat.)~±~0.18~(syst.) at s√ = 2.3960~GeV, ΔΦ = 55∘~±~19∘~(stat.) ±~14∘~(syst.) at s√ = 2.6454~GeV, and 78∘~±~22∘~(stat.) ±~9∘~(syst.) at s√ = 2.9000~GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.
The absolute branching fraction of the decay Λc(2625)+→Λ+cπ+π− is measured for the first time to be (50.7±5.0stat.±4.9syst.)% with 368.48 pb−1 of e+e− collision data collected by the BESIII detector at the center-of-mass energies of s√=4.918 and 4.950 GeV. This result is lower than the naive prediction of 67\%, obtained from isospin symmetry, by more than 2σ, thereby indicating that the novel mechanism referred to as the \textit{threshold effect}, proposed for the strong decays of Λc(2595)+, also applies to Λc(2625)+. This measurement is necessary to obtain the coupling constants for the transitions between s-wave and p-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Λc(2595)+→Λ+cπ+π−. No significant signal is observed, and the upper limit on its branching fraction is determined to be 80.8\% at the 90\% confidence level.