Σ+ and ¯Σ− Polarization in the J/ψ and ψ(3686) Decays

From 1310.6×106  J/ψ and 448.1×106  ψ(3686) events collected with the BESIII experiment, we report the first observation of Σ+ and ¯Σ− spin polarization in e+e−→J/ψ[ψ(3686)]→Σ+¯Σ− decays. The relative phases of the form factors ΔΦ have been measured to be (−15.5±0.7±0.5)° and (21.7±4.0±0.8)° with J/ψ and ψ(3686) data, respectively. The nonzero value of ΔΦ allows for a direct and simultaneous measurement of the decay asymmetry parameters of Σ+→pπ0(α0=−0.998±0.037±0.009) and ¯Σ−→¯pπ0(¯α0=0.990±0.037±0.011), the latter value being determined for the first time. The average decay asymmetry, (α0−¯α0)/2, is calculated to be −0.994±0.004±0.002. The CP asymmetry ACP,Σ=(α0+¯α0)/(α0−¯α0)=−0.004±0.037±0.010 is extracted for the first time, and is found to be consistent with CP conservatio

First Observation of D+→ημ+νμ and Measurement of Its Decay Dynamics

By analyzing a data sample corresponding to an integrated luminosity of 2.93  fb−1 collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the D+→ημ+νμ decay to be BD+→ημ+νμ=(10.4±1.0stat±0.5syst)×10−4. Using the world averaged value of BD+→ηe+νe, the ratio of the two branching fractions is determined to be BD+→ημ+νμ/BD+→ηe+νe=0.91±0.13(stat+syst), which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor fη+(0) and the c→d Cabibbo-Kobayashi-Maskawa matrix element |Vcd| to be fη+(0)|Vcd|=0.087±0.008stat±0.002syst. Taking the input of |Vcd| from the global fit in the standard model, we determine fη+(0)=0.39±0.04stat±0.01syst. On the other hand, using the value of fη+(0) calculated in theory, we find |Vcd|=0.242±0.022stat±0.006syst±0.033theory

Measurement of the Cross Section for e+e−→Ξ−¯Ξ+ and Observation of an Excited Ξ Baryon

Using a total of 11.0  fb−1 of e+e− collision data with center-of-mass energies between 4.009 and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process e+e−→Ξ−¯Ξ+ by means of a single baryon-tag method. After performing a fit to the dressed cross section of e+e−→Ξ−¯Ξ+, no significant ψ(4230) or ψ(4260) resonance is observed in the Ξ−¯Ξ+ final states, and upper limits at the 90% confidence level on ΓeeB for the processes ψ(4230)/ψ(4260)→Ξ−¯Ξ+ are determined. In addition, an excited Ξ baryon at 1820  MeV/c2 is observed with a statistical significance of 6.2–6.5σ by including the systematic uncertainty, and the mass and width are measured to be M=(1825.5±4.7±4.7)  MeV/c2 and Γ=(17.0±15.0±7.9)  MeV, which confirms the existence of the JP=32− state Ξ(1820)

Direct Measurement of the Branching Fractions B(ψ(3686)→J/ψX) and B(ψ(3770)→J/ψX), and Observation of the State R(3760) in e+e−→J/ψX

We report a measurement of the observed cross sections of e+e−→J/ψX based on 3.21  fb−1 of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. In analysis of the cross sections, we measured the decay branching fractions of B(ψ(3686)→J/ψX)=(64.4±0.6±1.6)% and B(ψ(3770)→J/ψX)=(0.5±0.2±0.1)% for the first time. The energy-dependent line shape of these cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays ψ(3686)→J/ψX and ψ(3770)→J/ψX. Instead, it can be better described with one more BW amplitude of the decay R(3760)→J/ψX. Under this assumption, we extracted the R(3760) mass MR(3760)=3766.2±3.8±0.4  MeV/c2 , total width ΓtotR(3760)=22.2±5.9±1.4  MeV, and product of leptonic width and decay branching fraction ΓeeR(3760)B[R(3760)→J/ψX]=(79.4±85.5±11.7)  eV. The significance of the R(3760) is 5.3σ. The first uncertainties of these measured quantities are from fits to the cross sections and second systematic

Study of Open-Charm Decays and Radiative Transitions of the X(3872

The processes X(3872)→D*0¯¯¯D0+c.c.,γJ/ψ,γψ(2S), and γD+D− are searched for in a 9.0  fb−1 data sample collected at center-of-mass energies between 4.178 and 4.278 GeV with the BESIII detector. We observe X(3872)→D*0¯D0+c.c. and find evidence for X(3872)→γJ/ψ with statistical significances of 7.4σ and 3.5σ, respectively. No evident signals for X(3872)→γψ(2S) and γD+D− are found, and the upper limit on the relative branching ratio Rγψ≡{B[X(3872)→γψ(2S)]}/{B[X(3872)→γJ/ψ]

Measurements of Absolute Branching Fractions of Fourteen Exclusive Hadronic D Decays to η

Using 2.93  fb−1 of e+e− collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first measurements of the absolute branching fractions of 14 hadronic D0(+) decays to exclusive final states with an η, e.g., D0→K−π+η, K0Sπ0η, K+K−η, K0SK0Sη, K−π+π0η, K0Sπ+π−η, K0Sπ0π0η, and π+π−π0η; D+→K0Sπ+η, K0SK+η, K−π+π+η, K0Sπ+π0η, π+π+π−η, and π+π0π0η. Among these decays, the D0→K−π+η and D+→K0Sπ+η decays have the largest branching fractions, which are B(D0→K−π+η)=(1.853±0.025stat±0.031syst)% and B(D+→K0Sπ+η)=(1.309±0.037stat±0.031syst)%, respectively. The charge-parity asymmetries for the six decays with highest event yields are determined, and no statistically significant charge-parity violation is found

Model-Independent Determination of the Spin of the Ω− and Its Polarization Alignment in ψ(3686)→Ω−¯Ω+

We present an analysis of the process ψ(3686)→Ω−¯Ω+ (Ω−→K−Λ, ¯Ω+→K+¯Λ, Λ→pπ−, ¯Λ→¯pπ+) based on a dataset of 448×106  ψ(3686) decays collected with the BESIII detector at the BEPCII electron-positron collider. The helicity amplitudes for the process ψ(3686)→Ω−¯Ω+ and the decay parameters of the subsequent decay Ω−→K−Λ (¯Ω+→K+¯Λ) are measured for the first time by a fit to the angular distribution of the complete decay chain, and the spin of the Ω− is determined to be 3/2 for the first time since its discovery more than 50 years ago

Observation of a Near-Threshold Structure in the K+ Recoil-Mass Spectra in e+e−→K+(D−sD*0+D*−sD0)

We report a study of the processes of e+e−→K+D−sD*0 and K+D*−sD0 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−sD*0 and D*−sD0 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−sD*0 and D*−sD0. However, the properties of the excess need further exploration with more statistic

"Table 1" of "Measurement of the e+e- -> π+ π- cross section between 600 and 900 MeV using initial state radiation"

Data from Table 1 of Erratum Results for the bare cross section σ bare π+π and the pion form factor together with their statistical uncertainties. The systematical uncertainties are given by 0.9

Measurements of the branching fractions for D+→KS0KS0K+, KS0KS0π+ and D0→KS0KS0, KS0KS0KS0

By analyzing 2.93 fb−1 of data taken at the ψ(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ → K0S K0S K +, D+ → K0S K0Sπ+, D0 → K0S K0S and D0 → K0S K0S K0S . They are determined to be B(D+ → K0S K0S K +) = (2.54 ± 0.05stat. ± 0.12sys.) × 10−3, B(D+ → K0S K0Sπ+) = (2.70 ± 0.05stat. ± 0.12sys.) × 10−3, B(D0 → K0S K0S ) = (1.67 ± 0.11stat. ± 0.11sys.) × 10−4 and B(D0 → K0S K0S K0S ) = (7.21 ± 0.33stat. ± 0.44sys.) × 10−4, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements