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By using 6.32 fb−1 of data collected with the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, we perform an amplitude analysis of the decay D+s ! K0S + 0 and determine the relative fractions and phase differences of different intermediate processes, which include K0S (770)+, K0S (1450)+, K (892)0 +, K (892)+ 0, and K (1410)0 +. With the detection efficiency based on the amplitude analysis results, the absolute branching fraction is measured to be B(D+s ! K0S + 0) = (5.43 ± 0.30stat ± 0.15syst) × 10−3.
The process 𝑒+𝑒−→𝜙𝜂′ has been studied for the first time in detail using data sample collected with the BESIII detector at the BEPCII collider at center of mass energies from 2.05 to 3.08 GeV. A resonance with quantum numbers 𝐽𝑃𝐶=1−− is observed with mass 𝑀=(2177.5±4.8(stat)±19.5(syst))MeV/𝑐2 and width Γ=(149.0±15.6(stat)±8.9(syst)) MeV with a statistical significance larger than 10𝜎, including systematic uncertainties. If the observed structure is identified with the 𝜙(2170), then the ratio of partial width between the 𝜙𝜂′ by BESIII and 𝜙𝜂 by BABAR is (ℬ𝑅𝜙𝜂Γ𝑅𝑒𝑒)/(ℬ𝑅𝜙𝜂′Γ𝑅𝑒𝑒)=0.23±0.10(stat)±0.18(syst), which is smaller than the prediction of the 𝑠¯𝑠𝑔 hybrid models by several orders of magnitude.
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 M R (3760 ) = 3766.2 ± 3.8 ± 0.4 MeV/c2, total width Γ tot R ( 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.
Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matter–antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry1. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon–antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ− baryon and its antiparticle2 Ξ¯+
, has enabled a direct determination of the weak-phase difference, (ξP − ξS) = (1.2 ± 3.4 ± 0.8) × 10−2 rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods3. Finally, we provide an independent measurement of the recently debated Λ decay parameter αΛ (refs. 4,5). The ΛΛ¯
asymmetry is in agreement with and compatible in precision to the most precise previous measurement.
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+→𝐾0 𝑆𝜋+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.
The decays D → K−π+π+π− and D → K−π+π 0 are studied in a sample of quantum-correlated DD¯ pairs produced through the process e+e− → ψ(3770) → DD¯, exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fb−1 . Here D indicates a quantum superposition of a D0 and a D¯ 0 meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle γ of the Unitarity Triangle in B− → DK− decays at the LHCb and Belle II experiments. The coherence factors are determined to be RK3π = 0.52+0.12−0.10 and RKππ0 = 0.78 ± 0.04, with values for the average strong-phase differences that are δ K3π D = (167+31−19)◦ and δKππ0D = (196+14−15◦ , where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the D → K−π+π+π− to yield results that will allow for a more sensitive measurement of γ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6◦.
We report new measurements of the branching fraction ℬ(𝐷+𝑠→ℓ+𝜈), where ℓ+ is either 𝜇+ or 𝜏+(→𝜋+¯𝜈𝜏), based on 6.32 fb−1 of electron-positron annihilation data collected by the BESIII experiment at six center-of-mass energy points between 4.178 and 4.226 GeV. Simultaneously floating the 𝐷+𝑠→𝜇+𝜈𝜇 and 𝐷+𝑠→𝜏+𝜈𝜏 components yields ℬ(𝐷+𝑠→𝜏+𝜈𝜏)=(5.21±0.25±0.17)×10−2, ℬ(𝐷+𝑠→𝜇+𝜈𝜇)=(5.35±0.13±0.16)×10−3, and the ratio of decay widths 𝑅=Γ(𝐷+𝑠→𝜏+𝜈𝜏)Γ(𝐷+𝑠→𝜇+𝜈𝜇)=9.73+0.61−0.58±0.36, where the first uncertainties are statistical and the second systematic. No evidence of 𝐶𝑃 asymmetry is observed in the decay rates 𝐷±𝑠→𝜇±𝜈𝜇 and 𝐷±𝑠→𝜏±𝜈𝜏: 𝐴𝐶𝑃(𝜇±𝜈)=(−1.2±2.5±1.0)% and 𝐴𝐶𝑃(𝜏±𝜈)=(+2.9±4.8±1.0)%. Constraining our measurement to the Standard Model expectation of lepton universality (𝑅=9.75), we find the more precise results ℬ(𝐷+𝑠→𝜏+𝜈𝜏)=(5.22±0.10±0.14)×10−2 and 𝐴𝐶𝑃(𝜏±𝜈𝜏)=(−0.1±1.9±1.0)%. Combining our results with inputs external to our analysis, we determine the 𝑐→¯𝑠 quark mixing matrix element, 𝐷+𝑠 decay constant, and ratio of the decay constants to be |𝑉𝑐𝑠|=0.973±0.009±0.014, 𝑓𝐷+𝑠=249.9±2.4±3.5 MeV, and 𝑓𝐷+𝑠/𝑓𝐷+=1.232±0.035, respectively.
Using 2.93 fb−1 of e+e− collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0→K1(1270)−e+νe semileptonic decay is presented. The statistical significance of the decay D0→K1(1270)−e+νe is greater than 10σ. The branching fraction of D0→K1(1270)−e+νe is measured to be (1.09±0.13+0.09−0.13±0.12)×10−3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)−→K−π+π−.
Using 2.93 fb−1 of e+e− collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0→K1(1270)−e+νe semileptonic decay is presented. The statistical significance of the decay D0→K1(1270)−e+νe is greater than 10σ. The branching fraction of D0→K1(1270)−e+νe is measured to be (1.09±0.13+0.09−0.16±0.12)×10−3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)−→K−π+π−. The fraction of longitudinal polarization in D0→K1(1270)−e+νe is determined for the first time to be 0.50±0.19stat±0.08syst.