Measurement of the CP -even fraction of D0 →π+π-π+π-

A measurement of the CP-even fraction of the decay D0→π+π-π+π- is performed with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment, corresponding to an integrated luminosity of 2.93 fb-1. Using a combination of CP eigenstates, D→π+π-π0 and D→KS,L0π+π- as tagging modes, the CP-even fraction is measured to be F+4π=0.735±0.015±0.005, where the first uncertainty is statistical and the second is systematic. This is the most precise determination of this quantity to date. It provides valuable model-independent input for the measurement of the angle γ of the Cabibbo-Kobayashi-Maskawa matrix with B±→DK± decays, and for time-dependent studies of CP violation and mixing in the D0-D¯0 system

Measurement of the cross section of e + e − → ηπ + π − at center-of-mass energies from 3.872 GeV to 4.700 GeV

Using data samples with an integrated luminosity of 19 fb−1 at twenty-eight center-of-mass energies from 3.872 GeV to 4.700 GeV collected with the BESIII detector at the BEPCII electron-positron collider, the process e+e− → ηπ+π− and the intermediate process e+e− → ηρ0 are studied for the first time. The Born cross sections are measured. No significant resonance structure is observed in the cross section lineshape. [Figure not available: see fulltext.]

Search for a massless dark photon in Λc+ →pγ′ decay

A search for a massless dark photon γ′ is conducted using 4.5 fb-1 of e+e- collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction B(Λc+→pγ′) is determined to be 8.0×10-5 at 90% confidence level

Observation of the doubly Cabibbo-suppressed decays D + → K + π 0 π 0 and D + → K + π 0 η

By analyzing e+e− annihilation data corresponding to an integrated luminosity of 2.93 fb−1 collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first observations of the doubly Cabibbo-suppressed decays D+→ K+π0π0 and D+→ K+π0η. The branching fractions of D+→ K+π0π0 and D+→ K+π0η are measured to be (2.1 ± 0.4stat ± 0.1syst) × 10−4 and (2.1 ± 0.5stat ± 0.1syst) × 10−4 with statistical significances of 8.8σ and 5.5σ, respectively. In addition, we search for the subprocesses D+→ K*(892)+π0 and D+→ K*(892)+η with K*(892)+→ K+π0. The branching fraction of D+→ K*(892)+η is determined to be (4.4−1.5stat+1.8± 0.2syst) × 10−4, with a statistical significance of 3.2σ. No significant signal for D+→ K*(892)+π0 is found and we set an upper limit on the branching fraction of this decay at the 90% confidence level to be 5.4 × 10−4. [Figure not available: see fulltext.

Improved measurement of the strong-phase difference δDKπ in quantum-correlated DD¯ decays

The decay D→ K-π+ is studied in a sample of quantum-correlated DD¯ pairs, based on a data set corresponding to an integrated luminosity of 2.93 fb- 1 collected at the ψ(3770) resonance by the BESIII experiment. The asymmetry between CP-odd and CP-even eigenstate decays into K-π+ is determined to be AKπ= 0.132 ± 0.011 ± 0.007 , where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a KL0 meson. The branching fractions of the KL0 modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D→ π+π-π and the ensemble of CP-odd eigenstate tags, the observable AKππππ0 is measured to be 0.130 ± 0.012 ± 0.008. The two asymmetries are sensitive to rDKπcosδDKπ, where rDKπ and δDKπ are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D→ K-π+ tagged by D→KS,L0π+π- are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both rDKπcosδDKπ and rDKπsinδDKπ. A fit to AKπ, AKππππ0 and the phase-space distribution of the D→KS,L0π+π- tags yields δDKπ=(187.6-9.7+8.9-6.4+5.4)∘, where external constraints are applied for rDKπ and other relevant parameters. This is the most precise measurement of δDKπ in quantum-correlated DD¯ decays

Study of e+e- → ω- ω ¯ + at center-of-mass energies from 3.49 to 3.67 GeV

Using data samples of e+e- collisions collected with the BESIII detector at eight center-of-mass energy points between 3.49 and 3.67 GeV, corresponding to an integrated luminosity of 670 pb-1, we present the upper limits of Born cross sections and the effective form factor for the process e+e-→ω-ω¯+. A fit to the cross sections using a perturbative QCD-derived energy-dependent function shows no significant threshold effect. The upper limit on the measured effective form factor is consistent with a theoretical prediction within the uncertainty of 1σ. These results provide new experimental information on the production mechanism of ω

Determination of spin and parity of D(s)⁎ mesons

The spin and parity of the charmed mesons Ds⁎+, D⁎0 and D⁎+ are determined for the first time to be JP=1− with significances greater than 10σ over other hypotheses of 2+ and 3−, using an e+e− collision data sample with an integrated luminosity of 3.19 fb−1 collected by the BESIII detector at a center-of-mass energy of 4.178 GeV. Different spin-parity hypotheses are tested via a helicity amplitude analysis of the processes e+e−→Ds⁎+Ds−, D⁎0D0 and D⁎+D−, with Ds⁎+→Ds+γ, D⁎0→D0π0, and D⁎+→D+π0. The results confirm the quark model predictions.</p

Observation of the decay ψ(3686) → Σ −Σ ¯ + and measurement of its angular distribution

Using (448.1 ± 2.9) × 106ψ(3686) events collected with the BESIII detector at the BEPCII collider, the decay ψ(3686) →Σ −Σ ¯ + is observed for the first time with a branching fraction of (2.82 ± 0.04stat.± 0.08syst.) × 10−4, and the angular parameter αΣ− is measured to be 0.96 ± 0.09stat.± 0.03syst.. [Figure not available: see fulltext.

Search for hyperon Δs= Δq violating decay Ξ0 → ς-e+νe

Using a data sample of (1.0087±0.0044)×1010 J/ψ decay events collected with the BESIII detector at the center-of-mass energy of s=3.097 GeV, we present a search for the hyperon semileptonic decay Ξ0→ς-e+νe which violates the ΔS=ΔQ rule. No significant signal is observed, and the upper limit on the branching fraction B(Ξ0→ς-e+νe) is determined to be 1.6×10-4 at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude