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Institute
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We measure the Born cross sections of the process 𝑒+𝑒−→𝐾+𝐾−𝐾+𝐾− at center-of-mass (c.m.) energies, √𝑠, between 2.100 and 3.080 GeV. The data were collected using the BESIII detector at the BEPCII collider. An enhancement at √𝑠=2.232 GeV is observed, very close to the 𝑒+𝑒−→Λ¯Λ production threshold. A similar enhancement at the same c.m. energy is observed in the 𝑒+𝑒−→𝜙𝐾+𝐾− cross section. The energy dependence of the 𝐾+𝐾−𝐾+𝐾− and 𝜙𝐾+𝐾− cross sections differs significantly from that of 𝑒+𝑒−→𝜙𝜋+𝜋−.
The CP-even fractions (F+) of the decays D0→π+π−π0 and D0→K+K−π0 are measured with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment corresponding to an integrated luminosity of 7.93 fb−1. The results are Fπ+π−π0+=0.9406±0.0036±0.0021 and FK+K−π0+=0.631±0.014±0.011, where the first uncertainties are statistical and the second systematic. These measurements are consistent with the previous determinations, and the uncertainties for Fπ+π−π0+ and FK+K−π0+ are reduced by factors of 3.9 and 2.6, respectively. The reported results provide important inputs for the precise measurement of the angle γ of the Cabibbo-Kobayashi-Maskawa matrix and indirect CP violation in charm mixing.
In the effective field theory, the massless dark photon γ′ can only couple with the Standard Model particle through operators of dimension higher than four, thereby offering a high sensitivity to the new physics energy scale. Using 7.9 fb−1 of e+e− collision data collected at s√=3.773 GeV with the BESIII detector at the BEPCII collider, we measure the effective flavor-changing neutral current coupling of cuγ′ in D0→ωγ′ and D0→γγ′ processes to search for the massless dark photon. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be 1.1×10−5 and 2.0×10−6 for D0→ωγ′ and D0→γγ′, respectively. These results provide the most stringent constraint on the new physics energy scale associated with cuγ′ coupling in the world, with the new physics energy scale related parameter |C|2+|C5|2<8.2×10−17 GeV−2 at the 90% confidence level, playing a unique role in the dark sector search with the charm sector.
Model-independent determination of the strong-phase difference between D⁰ and D̄⁰ → π⁺π⁻π⁺π⁻ decays
(2024)
Measurements of the strong-phase difference between D0 and D¯0→π+π−π+π− are performed in bins of phase space. The study exploits a sample of quantum-correlated DD¯ mesons collected by the BESIII experiment in e+e− collisions at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 2.93~fb−1. Here, D denotes a neutral charm meson in a superposition of flavor eigenstates. The reported results are valuable for measurements of the CP-violating phase γ (also denoted ϕ3) in B±→DK±, D→π+π−π+π− decays, and the binning schemes are designed to provide good statistical sensitivity to this parameter. The expected uncertainty on γ arising from the precision of the strong-phase measurements, when applied to very large samples of B-meson decays, is around 1.5∘ or 2∘, depending on the binning scheme. The binned strong-phase parameters are combined to give a value of F4π+=0.746±0.010±0.004 for the CP-even fraction of D0→π+π−π+π− decays, which is around 30\% more precise than the previous best measurement of this quantity.
Using 7.93 fb−1 of e+e− collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we measure the absolute branching fractions of D0→K−e+νe, D0→K−μ+νμ, D+→K¯0e+νe, and D+→K¯0μ+νμ to be (3.509±0.009stat.±0.013syst.)%, (3.408±0.011stat.±0.013syst.)%, (8.856±0.039stat.±0.078syst.)%, and (8.661±0.046stat.±0.080syst.)%, respectively. By performing a simultaneous fit to the partial decay rates of these four decays, the product of the hadronic form factor fK+(0) and the modulus of the c→s CKM matrix element |Vcs| is determined to be fK+(0)|Vcs|=0.7162±0.0011stat.±0.0012syst.. Taking the value of |Vcs|=0.97349±0.00016 from the standard model global fit or that of fK+(0)=0.7452±0.0031 from the LQCD calculation as input, we derive the results fK+(0)=0.7357±0.0011stat.±0.0012syst. and |Vcs|=0.9611±0.0015stat.±0.0016syst.±0.0040LQCD.
Using (2712.4±14.3)×106 ψ(3686) events collected with the BESIII detector operating at the BEPCII collider, we search for the hadronic transition hc→π+π−J/ψ via ψ(3686)→π0hc. No significant signal is observed. We set the most stringent upper limits to date on the branching fractions B(ψ(3686)→π0hc)×B(hc→π+π−J/ψ) and B(hc→π+π−J/ψ) at the 90% confidence level, which are determined to be 6.7×10−7 and 9.4×10−4, respectively.
We perform the first investigation of the process e+e−→K+K−ψ(2S) and report its Born cross sections over a range of center-of-mass energies from 4.699 to 4.951~GeV. The measurements are carried out using several partial reconstruction techniques using data samples collected by the BESIII detector with a total integrated luminosity of 2.5~fb−1. We search for new tetraquark candidates Z±cs in the decays Z±cs→K±ψ(2S). No significant Z±cs signals are observed.
The e+e−→D+sDs1(2536)− and e+e−→D+sD∗s2(2573)− processes are studied using data samples collected with the BESIII detector at center-of-mass energies from 4.530 to 4.946~GeV. The absolute branching fractions of Ds1(2536)−→D¯∗0K− and D∗s2(2573)−→D¯0K− are measured for the first time to be (35.9±4.8±3.5)% and (37.4±3.1±4.6)%, respectively. The measurements are in tension with predictions based on the assumption that the Ds1(2536) and D∗s2(2573) are dominated by a bare cs¯ component. The e+e−→D+sDs1(2536)− and e+e−→D+sD∗s2(2573)− cross sections are measured, and a resonant structure at around 4.6~GeV with a width of 50~MeV is observed for the first time with a statistical significance of 15σ in the e+e−→D+sD∗s2(2573)− process. It could be the Y(4626) found by the Belle collaboration in the D+sDs1(2536)− final state, since they have similar masses and widths. There is also evidence for a structure at around 4.75~GeV in both processes.
The branching fraction of D+→K0Sπ0e+νe is measured for the first time using 7.93 fb−1 of e+e− annihilation data collected at the center-of-mass energy s√=3.773~GeV with the BESIII detector operating at the BEPCII collider, and is determined to be B(D+→K0Sπ0e+νe) = (0.881 ± 0.017stat. ± 0.016syst.)\%. Based on an analysis of the D+→K0Sπ0e+νe decay dynamics, we observe the S-wave and P-wave components with fractions of fS-wave = (6.13 ± 0.27stat. ± 0.30syst.)% and fK¯∗(892)0 = (93.88 ± 0.27stat. ± 0.29syst.)\%, respectively. From these results, we obtain the branching fractions B(D+→(K0Sπ0)S-wave e+νe) = (5.41 ± 0.35stat. ± 0.37syst.)×10−4 and B(D+→K¯∗(892)0e+νe) = (4.97 ± 0.11stat. ± 0.12syst.)\%. In addition, the hadronic form-factor ratios of D+→K¯∗(892)0e+νe at q2=0, assuming a single-pole dominance parameterization, are determined to be rV=V(0)A1(0)=1.43 ± 0.07stat. ± 0.03syst. and r2=A2(0)A1(0)=0.72 ± 0.06stat. ± 0.02syst.