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Institute
- Physik (371)
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.
We report on the first search for ¯Λ−Λ oscillations in the decay 𝐽/𝜓→𝑝𝐾−¯Λ+c.c. by analyzing 1.31×109 𝐽/𝜓 events accumulated with the BESIII detector at the BEPCII collider. The 𝐽/𝜓 events are produced using 𝑒+𝑒− collisions at a center of mass energy √𝑠=3.097 GeV. No evidence for hyperon oscillations is observed. The upper limit for the oscillation rate of ¯Λ to Λ hyperons is determined to be 𝒫(Λ)=[ℬ(𝐽/𝜓→𝑝𝐾−Λ+c.c.)/ℬ(𝐽/𝜓→𝑝𝐾−¯Λ+c.c.)]<4.4×10−6 corresponding to an oscillation parameter 𝛿𝑚Λ¯Λ of less than 3.8×10−18 GeV at the 90% confidence level.
We present cross sections for the reaction e+e−→K0SK0L at center-of-mass energies ranging from 3.51 GeV to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb−1. The ratio of neutral-to-charged kaon form factors at large momentum transfers (12 GeV2<Q2<25 GeV2) is determined to be 0.21±0.01, which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and consequently excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction |F(π±)|/|F(K±)|=f2π/f2K, where F(π±) and F(K±) are the form factors, and fπ and fK are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay ψ(3770)→K0SK0L for the first time. Within a 1σ contour of the likelihood value, the the branching fraction for ψ(3770)→K0SK0L is determined to be B=(2.63+1.40−1.59)×10−5, and the relative phase between the continuum and ψ(3770) amplitudes is ϕ=(−0.39+0.05−0.10)π. The branching fraction is in good agreement with the S- and D-wave charmonia mixing scheme proposed in the interpretation of the "ρπ puzzle" between J/ψ and ψ(3686) decays.
A search has been performed for the semileptonic decays D0→K0SK−e+νe, D+→K0SK0Se+νe and D+→K+K−e+νe, using 7.9 fb−1 of e+e− annihilation data collected at the center-of-mass energy s√=3.773 GeV by the BESIII detector operating at the BEPCII collider. No significant signals are observed, and upper limits are set at the 90\% confidence level of 2.13×10−5, 1.54×10−5 and 2.10×10−5 for the branching fractions of D0→K0SK−e+νe, D+→K0SK0Se+νe and D+→K+K−e+νe, respectively.
The decays of χc2→K+K−π0, KSK±π∓ and π+π−π0 are studied with the ψ(3686) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of χc2→K∗K¯¯¯¯¯, χc2→a±2(1320)π∓/a02(1320)π0 and χc2→ρ(770)±π∓ are measured. Here K∗K¯¯¯¯¯ denotes both K∗±K∓ and K∗0K¯¯¯¯¯0+c.c., and K∗ denotes the resonances K∗(892), K∗2(1430) and K∗3(1780). The observations indicate a strong violation of the helicity selection rule in χc2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of χc2→K∗(892)K¯¯¯¯¯ are more than 20 times larger than that of χc2→ρ(770)±π∓, which implies the effects are largely due to U-spin symmetry breaking, rather than just isospin symmetry breaking in charmonium decays.
Analyzing (448.1±2.9)×106 ψ(3686) events collected with the BESIII detector at the BEPCII collider, the ψ(3686)→ωK0SK0S decay is observed for the first time. The branching fraction for this decay is determined to be Bψ(3686)→ωK0SK0S=(7.04±0.39±0.36)×10−5, where the first uncertainty is statistical and the second is systematic.
Observation of three charmonium-like states with JPC = 1⁻⁻ in e⁺e⁻− → D*⁰D*⁻π⁺ + c.c. process
(2023)
The Born cross sections of the process e+e−→D∗0D∗−π++c.c. at center-of-mass energies from 4.189 to 4.951 GeV are measured for the first time. The data samples used correspond to an integrated luminosity of 17.9fb−1 and were collected by the BESIII detector operating at the BEPCII storage ring. Three enhancements around 4.20, 4.47 and 4.67 GeV are visible. The resonances have masses of 4209.6±4.7±5.9MeV/c2, 4469.1±26.2±3.6MeV/c2 and 4675.3±29.5±3.5MeV/c2 and widths of 81.6±17.8±9.0MeV, 246.3±36.7±9.4MeV and 218.3±72.9±9.3MeV, respectively, where the first uncertainties are statistical and the second systematic. The first and third resonances are consistent with the Y(4230) and Y(4660) states, respectively, while the second one is compatible with the Y(4500) observed in the e+e−→K+K−J/ψ process. These three Y states are observed in e+e−→D∗0D∗−π++c.c. process for the first time.