Sheng-Sen Sun

Using an e + e − sample of 20.3 fb − 1 collected at a center-of-mass energy s = 3.773 GeV with the BESIII detector, we report measurements of several four-body hadronic decays of D mesons. All studied decay modes are dominated by Cabibbo-favored amplitudes. The absolute branching fractions are determined to be B ( D 0 → K S 0 K S 0 K S 0 π 0 ) = ( 7.8 − 2.0 + 2.3 ± 1.5 ) × 10 − 5 , B ( D 0 → K S 0 K + K − π 0 ) = ( 18.4 − 2.5 + 2.6 ± 2.4 ) × 10 − 5 , B ( D 0 → K S 0 K S 0 K − π + ) = ( 12.9 − 1.6 + 1.7 ± 1.3 ) × 10 − 5 , B ( D 0 → K S 0 K S 0 K + π − ) = ( 5.7 − 1.1 + 1.2 ± 1.0 ) × 10 − 5 , B ( D 0 → K + K − K − π + ) = ( 17.4 − 1.7 + 1.8 ± 2.2 ) × 10 − 5 , B ( D + → K S 0 K S 0 K S 0 π + ) = ( 6.0 − 1.7 + 2.1 ± 1.6 ) × 10 − 5 , and B ( D + → K S 0 K + K − π + ) = ( 13.8 − 2.2 + 2.4 ± 2.5 ) × 10 − 5 . Furthermore, significant ϕ signals are found in the decay channels involving a K + K − pair, and their fractions are determined as B ( D 0 → ϕ K S 0 π 0 ) / B ( D 0 → K S 0 K + K − π 0 ) = ( 6 1 − 14 + 15 ± 10 ) % , B ( D 0 → ϕ K − π + ) / B ( D 0 → K + K − K − π + ) = ( 7 1 − 10 + 10 ± 13 ) % , and B ( D + → ϕ K S 0 π + ) / B ( D + → K S 0 K + K − π + ) = ( 5 9 − 19 + 22 ± 9 ) % . The branching fractions of D 0 → K S 0 K S 0 K S 0 π 0 , D 0 → K S 0 K + K − π 0 , and D + → K S 0 K S 0 K S 0 π + are measured for the first time, and those of D 0 → K S 0 K S 0 K − π + , D 0 → K S 0 K S 0 K + π − , D 0 → K + K − K − π + , D 0 → ϕ K − π + , and D + → K S 0 K + K − π + are measured with improved precision. The first uncertainties are statistical and the second are systematic.

Based on an integrated luminosity of 20.3 fb − 1 of e + e − annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector operating at the BEPCII collider, an improved search for the radiative transitions ψ ( 3770 ) → γ η c ( 1 S , 2 S ) is performed using the hadronic decays η c ( 1 S , 2 S ) → K S 0 K ± π ∓ . No significant signal is observed. The corresponding 90% confidence level upper limits on the product branching fractions are set to be 5.0 × 10 − 6 for the η c ( 1 S ) transition and 3.7 × 10 − 6 for the η c ( 2 S ) transition. The 90% confidence level upper limits on the partial decay widths are also reported to be Γ ( ψ ( 3770 ) → γ η c ( 1 S ) ) < 5.5 keV and Γ ( ψ ( 3770 ) → γ η c ( 2 S ) ) < 29.4 keV . With about seven times larger integrated luminosity than used previously, these results lower the upper limits by approximately a factor of three and two for the η c ( 1 S ) and η c ( 2 S ) transitions, respectively.

Using 44.55 fb − 1 of e + e − collision data collected by the BESIII detector at the BEPCII collider, we report the first measurement of the Born cross sections for the e + e − → K + Ξ 0 Σ ¯ − reaction at 56 center-of-mass energies between 3.51 and 4.95 GeV. A fit to the dressed cross sections reveals the first observation of the ψ ( 3770 ) → K + Ξ 0 Σ ¯ − process, with a statistical significance of 6.0 σ including systematic uncertainties. This result represents the first observation of charmless three-body baryonic decay of a vector charmonium state above the open-charm threshold, providing important experimental input for studying the origin of the large non- D D ¯ component of the ψ ( 3770 ) decay width. No significant signals for other charmonium(like) states i.e., ψ ( 4040 ) , ψ ( 4160 ) , Y ( 4230 ) , Y ( 4360 ) , ψ ( 4415 ) , Y ( 4500 ) , Y ( 4660 ) or Y ( 4710 ) are observed, and the upper limits for the product of the branching fraction and the electronic partial width at the 90% confidence level for each assumed charmonium(like) state are provided. Additionally, the ratios of Born cross sections between this work and the previous measurements of e + e − → K S 0 Ξ ¯ + Σ − and K − Ξ ¯ + Σ 0 are provided, which can be used to validate theoretical predictions related to isospin symmetry.

Based on ( 10.087 ± 0.044 ) × 10 9 J / ψ events collected at the center-of-mass energy s = 3.097 GeV with the BESIII detector, we search for the charged lepton flavor violating decay η → e ± μ ∓ through the process J / ψ → γ η ′ with η ′ → π + π − η . No signal is observed, and an upper limit on the branching fraction is determined to be B ( η → e ± μ ∓ ) < 6.8 × 10 − 7 at the 90% confidence level. This result improves the previous best limit by one order of magnitude.

Using e + e − collision data corresponding to an integrated luminosity of 44 fb − 1 collected with the BESIII detector at the BEPCII Collider, we report the first measurement of Born cross sections and effective form factors for e + e − → Σ − Σ ¯ + at center-of-mass energies between 3.51 and 4.95 GeV. With a fit to the s -dependent dressed cross sections, the decay ψ ( 3770 ) → Σ − Σ ¯ + is observed for the first time with a significance of 5.5 σ , including systematic uncertainties. The corresponding branching fraction is determined to have two solutions, ( 2.9 ± 0.3 ) × 10 − 4 and ( 1.1 ± 0.1 ) × 10 − 4 , where the quoted uncertainties also include systematic uncertainties. Upper limits at the 90% confidence level on the product of the branching fraction and the electronic partial width are provided for other possible charmonium(like) states. The ratios of Born cross sections for the Σ isospin-triplet states are determined and can be used to test the vector-meson-dominance model.

The CEPC clock issue is related with the RF frequency coordination between the various accelerator systems and may affect the operation modes of both the accelerator and the detector. The timing structure of CEPC has been restudied with the collaboration of the accelerator team and the detector team. After discussions between two sides, the CEPC bunch structure is set such that the spacings between adjacent bunches in any CEPC operation mode are integer numbers of 23.08[Formula: see text]ns. The master CEPC clock will be provided by the accelerator to the detector systems with a frequency of 43.33[Formula: see text]MHz, synchronous to the beam. The CEPC detector system relies on the clock to sample physics signal at the right time. It was found that if the circumference of CEPC is slightly changed to 99955.42[Formula: see text]m, the detector would benefit more for the first 10-year operation.

By analyzing a sample of 20.3 fb − 1 of e + e − annihilation data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we have made a first measurement of the absolute branching fractions of the radiative decays D 0 → γ K ¯ * 0 and D 0 → γ ϕ to be ( 3.81 ± 0.1 8 stat ± 0.2 0 syst ) × 10 − 4 and ( 2.51 ± 0.4 4 stat ± 0.1 1 syst ) × 10 − 5 , respectively. The statistical significances of D 0 → γ K ¯ * 0 and D 0 → γ ϕ are 26.8 σ and 7.9 σ , respectively. The obtained branching fractions are consistent with the corresponding world average values. In addition, the measured C P asymmetry A C P ( D 0 → γ K ¯ * 0 ) = ( − 0.7 ± 5.0 stat ± 4.1 syst ) % is consistent with C P conservation.

We report a study of the semileptonic decays D 0 → K ¯ 0 π − ℓ + ν ℓ (where ℓ = e , μ ) based on a sample of 20.3 fb − 1 of e + e − annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. Based on an investigation of the decay dynamics in D 0 → K ¯ 0 π − ℓ + ν ℓ decays, a D -wave component of D 0 → K 2 * ( 1430 ) − ℓ + ν ℓ is observed for the first time with a statistical significance of 8.0 σ , in addition to the dominant K * ( 892 ) − and S -wave components. The D -wave component is determined to account for ( 0.092 ± 0.02 8 stat ± 0.01 8 syst ) % of the total decay rate. The branching fractions of the dominant K * ( 892 ) − components are measured as B ( D 0 → K * ( 892 ) − e + ν e ) = ( 2.043 ± 0.01 8 stat ± 0.01 2 syst ) % and B ( D 0 → K * ( 892 ) − μ + ν μ ) = ( 1.964 ± 0.01 8 stat ± 0.01 2 syst ) % , which are the most precise measurements to date and represent significant improvements over the previous world averages. The hadronic form-factor parameters are measured to be r V = V ( 0 ) / A 1 ( 0 ) = 1.444 ± 0.02 6 stat ± 0.01 0 syst , r 2 = A 2 ( 0 ) / A 1 ( 0 ) = 0.752 ± 0.02 0 stat ± 0.00 4 syst , and A 1 ( 0 ) = 0.618 ± 0.00 2 stat ± 0.00 4 syst , where V ( 0 ) is the vector form factor and A 1 , 2 ( 0 ) are the axial-vector form factors evaluated at q 2 = 0 . This is the most precise determination of the form-factor parameters to date measured in a D → K * ( 892 ) transition. In addition, we report the first model-independent measurement of the S -wave phase shift in the hadronic K ¯ 0 π − system. We also measure the relative ratio between branching fractions of D 0 → K * ( 892 ) − μ + ν μ and D 0 → K * ( 892 ) − μ + ν μ to be R K * ( 892 ) μ / e = 0.961 ± 0.01 2 stat ± 0.00 5 syst , and no violation of lepton flavor universality is found.

Based on events collected with the BESIII detector, the and processes are studied. The is observed in both the and invariant mass spectra, with statistical significances greater than and , respectively. By combining measurements from these processes with those from the previously reported process, the mass and width of the are determined to be and , respectively. In addition, the decay with is observed with a statistical significance exceeding . The properties of the —decay pattern similarities to that of , are consistent with those of a pseudoscalar glueball.