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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 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.
We study ηc production at center-of-mass energies s√ from 4.18 to 4.60 GeV in e+e− annihilation data collected with the BESIII detector operating at the BEPCII storage ring, corresponding to 7.3 fb−1 of integrated luminosity. We measure the cross sections of the three different exclusive reactions e+e−→ηcπ+π−π0, e+e−→ηcπ+π−, and e+e−→ηcπ0γ. We find significant ηc production in e+e−→ηcπ+π−π0 at s√ of 4.23 GeV and 4.26 GeV and observe a significant energy-dependent Born cross section that we measure to be consistent with the production via the intermediate Y(4260) resonance. In addition, we perform a search for a charmonium-like Zc state close to the DD¯ threshold that decays to ηcπ, involving ground state charmonium, and observe no signal. Corresponding upper limits on the cross section of ηc and Zc production are provided, where the yields are not found to be significant.
Based on 2.93~fb−1 e+e− collision data taken at center-of-mass energy of 3.773 GeV by the BESIII detector, we report the measurements of the absolute branching fractions of D0→K+K−π0π0, D0→K0SK0Sπ+π−, D0→K0SK−π+π0, D0→K0SK+π−π0, D+→K+K−π+π0, D+→K0SK+π0π0, D+→K0SK−π+π+, D+→K0SK+π+π−, and D+→K0SK0Sπ+π0. The decays D0→K+K−π0π0, D0→K0SK−π+π0, D0→K0SK+π−π0, D+→K0SK0Sπ+π0, and D+→K0SK+π0π0 are observed for the first time. The branching fractions of the decays D0→K0SK0Sπ+π−, D+→K+K−π+π0, D+→K0SK−π+π+, and D+→K0SK+π+π− are measured with improved precision compared to the world-average values.
The singly Cabibbo-suppressed decay Λ+c→nπ+ is observed for the first time with a statistical significance of 7.3σ by using 3.9 fb−1 of e+e− collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ+c→nπ+ is measured to be (6.6±1.2stat±0.4syst)×10−4. By taking the upper limit of branching fractions of Λ+c→pπ0 from the Belle experiment, the ratio of branching fractions between Λ+c→nπ+ and Λ+c→pπ0 is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with the current predictions of available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ+c→Λπ+ and Λ+c→Σ0π+ are measured to be (1.31±0.08stat±0.05syst)×10−2 and (1.22±0.08stat±0.07syst)×10−2, respectively, which are consistent with previous results.
The singly Cabibbo-suppressed decay Λ+c→nπ+ is observed for the first time with a statistical significance of 7.3σ by using 3.9 fb−1 of e+e− collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ+c→nπ+ is measured to be (6.6±1.2stat±0.4syst)×10−4. By taking the upper limit of branching fractions of Λ+c→pπ0 from the Belle experiment, the ratio of branching fractions between Λ+c→nπ+ and Λ+c→pπ0 is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with the current predictions of available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ+c→Λπ+ and Λ+c→Σ0π+ are measured to be (1.31±0.08stat±0.05syst)×10−2 and (1.22±0.08stat±0.07syst)×10−2, respectively, which are consistent with previous results.
The singly Cabibbo-suppressed decay Λ+c→nπ+ is observed for the first time with a statistical significance of 7.3σ by using 3.9 fb−1 of e+e− collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ+c→nπ+ is measured to be (6.6±1.2stat±0.4syst)×10−4. By taking the upper limit of branching fractions of Λ+c→pπ0 from the Belle experiment, the ratio of branching fractions between Λ+c→nπ+ and Λ+c→pπ0 is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with the current predictions of available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ+c→Λπ+ and Λ+c→Σ0π+ are measured to be (1.31±0.08stat±0.05syst)×10−2 and (1.22±0.08stat±0.07syst)×10−2, respectively, which are consistent with previous results.
Using an 𝑒+𝑒− collision data sample of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of 𝐷0→𝑎0(980)−𝑒+𝜈𝑒 and evidence for 𝐷+→𝑎0(980)0𝑒+𝜈𝑒 with significances of 6.4𝜎 and 2.9𝜎, respectively. The absolute branching fractions are determined to be ℬ(𝐷0→𝑎0(980)−𝑒+𝜈𝑒)×ℬ(𝑎0(980)−→𝜂𝜋−) = [1.33+0.33−0.29(stat)±0.09(syst)]×10−4 and ℬ(𝐷+→𝑎0(980)0𝑒+𝜈𝑒)×ℬ(𝑎0(980)0→𝜂𝜋0)=[1.66+0.81
−0.66(stat)±0.11(syst)]×10−4. This is the first time the 𝑎0(980) meson has been measured in a 𝐷0 semileptonic decay, which would open one more interesting page in the investigation of the nature of the puzzling 𝑎0(980) states.
We study the hadronic decays of Λ+c to the final states Σ+η and Σ+η′, using an e+e− annihilation data sample of 567 pb−1 taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays Λ+c→Σ+η and Σ+η′ with statistical significance of 2.5σ and 3.2σ, respectively. Normalizing to the reference decays Λ+c→Σ+π0 and Σ+ω, we obtain the ratios of the branching fractions B(Λ+c→Σ+η)B(Λ+c→Σ+π0) and B(Λ+c→Σ+η′)B(Λ+c→Σ+ω) to be 0.35±0.16±0.03 and 0.86±0.34±0.07, respectively. The upper limits at the 90\% confidence level are set to be B(Λ+c→Σ+η)B(Λ+c→Σ+π0)<0.58 and B(Λ+c→Σ+η′)B(Λ+c→Σ+ω)<1.2. Using BESIII measurements of the branching fractions of the reference decays, we determine B(Λ+c→Σ+η)=(0.41±0.19±0.05)% (<0.68%) and B(Λ+c→Σ+η′)=(1.34±0.53±0.21)% (<1.9%). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of Λ+c→Σ+η is consistent with the previous measurement, and the branching fraction of Λ+c→Σ+η′ is measured for the first time.
We report a search for a dark photon using 14.9~fb−1 of e+e− annihilation data taken at center-of-mass energies from 4.13 to 4.60~GeV with the BESIII detector operated at the BEPCII storage ring. The dark photon is assumed to be produced in the radiative annihilation process of e+e− and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9~GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90% confidence level on the coupling strength parameter ϵ for a dark photon coupling with an ordinary photon vary between 1.6×10−3 and 5.7×10−3.
Using e+e− collision data samples with center-of-mass energies ranging from 2.000 to 2.644 GeV, collected by the BESIII detector at the BEPCII collider, and with a total integrated luminosity of 300 pb^{-1}, a partial-wave analysis is performed for the process e+e−→K+K−π0π0. The total Born cross sections for the process e+e−→K+K−π0π0, as well as the Born cross sections f or the subprocesses e+e−→ϕπ0π0, K+(1460)K−, K+1(1400)K−, K+1(1270)K− and K∗+(892)K∗−(892), are measured versus the center-of-mass energy. The corresponding results for e+e−→K+K−π0π0 and ϕπ0π0 are consistent with those of BaBar and have much improved this http URL analyzing the cross sections for the four subprocesses, K+(1460)K−, K+1(1400)K−, K+1(1270)K− and K∗+K∗−, a structure with mass M = (2126.5 ± 16.8 ± 12.4)~MeV/c^{2} and width Γ = (106.9 ± 32.1 ± 28.1)~MeV is observed with an overall statistical significance of 6.3 σ, although with very limited significance in the subprocesses e+e−→K+1(1270)K− and K∗+(892)K∗−(892). The resonant parameters of the observed structure suggest it can be identified with the ϕ(2170), thus the results provide valuable input to the internal nature of the ϕ(2170).