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The processes 𝑒+𝑒−→𝐷+ 𝑠𝐷𝑠1(2460)−+c.c. and 𝑒+𝑒−→𝐷*+ 𝑠𝐷𝑠1(2460)−+c.c. are studied for the first time using data samples collected with the BESIII detector at the BEPCII collider. The Born cross sections of 𝑒+𝑒−→𝐷+ 𝑠𝐷𝑠1(2460)−+c.c. at nine center-of-mass energies between 4.467 GeV and 4.600 GeV and those of 𝑒+𝑒−→𝐷*+ 𝑠𝐷𝑠1(2460)−+c.c. at √𝑠=4.590 GeV and 4.600 GeV are measured. No obvious charmonium or charmoniumlike structure is seen in the measured cross sections.
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.
Using 2.93 fb−1 of 𝑒+𝑒− collision data taken at a center-of-mass energy of 3.773 GeV by the BESIII detector at the BEPCII, we measure the branching fractions of the singly Cabibbo-suppressed decays 𝐷→𝜔𝜋𝜋 to be ℬ(𝐷0→𝜔𝜋+𝜋−)=(1.33±0.16±0.12)×10−3 and ℬ(𝐷+→𝜔𝜋+𝜋0)=(3.87±0.83±0.25)×10−3, where the first uncertainties are statistical and the second ones systematic. The statistical significances are 12.9𝜎 and 7.7𝜎, respectively. The precision of ℬ(𝐷0→𝜔𝜋+𝜋−) is improved by a factor of 2.1 over prior measurements, and ℬ(𝐷+→𝜔𝜋+𝜋0) is measured for the first time. No significant signal for 𝐷0→𝜔𝜋0𝜋0 is observed, and the upper limit on the branching fraction is ℬ(𝐷0→𝜔𝜋0𝜋0)<1.10×10−3 at the 90% confidence level. The branching fractions of 𝐷→𝜂𝜋𝜋 are also measured and consistent with existing results.
Cross sections of the process 𝑒+𝑒−→𝜋0𝜋0𝐽/𝜓 at center-of-mass energies between 3.808 and 4.600 GeV are measured with high precision by using 12.4 fb−1 of data samples collected with the BESIII detector operating at the BEPCII collider facility. A fit to the measured energy-dependent cross sections confirms the existence of the charmoniumlike state 𝑌(4220). The mass and width of the 𝑌(4220) are determined to be (4220.4±2.4±2.3) MeV/𝑐2 and (46.2±4.7±2.1) MeV, respectively, where the first uncertainties are statistical and the second systematic. The mass and width are consistent with those measured in the process 𝑒+𝑒−→𝜋+𝜋−𝐽/𝜓. The neutral charmonium-like state 𝑍𝑐(3900)0 is observed prominently in the 𝜋0𝐽/𝜓 invariant-mass spectrum, and, for the first time, an amplitude analysis is performed to study its properties. The spin-parity of 𝑍𝑐(3900)0 is determined to be 𝐽𝑃=1+, and the pole position is (3893.1±2.2±3.0)−𝑖(22.2±2.6±7.0) MeV/𝑐2, which is consistent with previous studies of electrically charged 𝑍𝑐(3900)±. In addition, cross sections of 𝑒+𝑒− → 𝜋0𝑍𝑐(3900)0 → 𝜋0𝜋0𝐽/𝜓 are extracted, and the corresponding line shape is found to agree with that of the 𝑌(4220).
The electromagnetic process is studied with the initial-state-radiation technique using 7.5 fb−1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/ using the invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
We report the first observation of the semimuonic decay 𝐷+→𝜔𝜇+𝜈𝜇 using an 𝑒+𝑒− collision data sample corresponding to an integrated luminosity of 2.93 fb−1 collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. The absolute branching fraction of the 𝐷+→𝜔𝜇+𝜈𝜇 decay is measured to be ℬ𝐷+→𝜔𝜇+𝜈𝜇=(17.7±1.8stat±1.1syst)×10−4. Its ratio with the world average value of the branching fraction of the 𝐷+→𝜔𝑒+𝜈𝑒 decay probes lepton flavor universality and it is determined to be ℬ𝐷+→𝜔𝜇+𝜈𝜇/ℬPDG 𝐷+→𝜔𝑒+𝜈𝑒=1.05±0.14, in agreement with the standard model expectation within one standard deviation.
Measurement of cross sections for e⁺e⁻ → μ⁺μ⁻ at center-of-mass energies from 3.80 to 4.60 GeV
(2020)
The observed cross sections for 𝑒+𝑒−→𝜇+𝜇− at energies from 3.8 to 4.6 GeV are measured using data samples taken with the BESIII detector operated at the BEPCII collider. We measure the muonic widths and determine the branching fractions of the charmonium states 𝜓(4040), 𝜓(4160), and 𝜓(4415) decaying to 𝜇+𝜇−, as well as making a first determination of the phase of the amplitudes. In addition, we observe evidence for a structure in the dimuon cross section near 4.220 GeV/𝑐2, which we denote as 𝑆(4220). Analyzing a coherent sum of amplitudes yields eight solutions, one of which gives a mass of 𝑀𝑆(4220) = 4216.7±8.9±4.1 MeV/𝑐2, a total width of Γtot S(4220) = 47.2±22.8±10.5 MeV, and a muonic width of Γ𝜇𝜇 𝑆(4220) = 1.53±1.26±0.54 keV, where the first uncertainties are statistical and the second systematic. The eight solutions give the central values of the mass, total width, muonic width to be, respectively, in the range from 4212.8 to 4219.4 MeV/𝑐2, from 36.4 to 49.6 MeV, and from 1.09 to 1.53 keV. The statistical significance of the 𝑆(4220) signal is 3.9𝜎. Correcting the total dimuon cross section for radiative effects yields a statistical significance for this structure of 8.1𝜎.
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.
Using a sample of 106 million 𝜓(3686) decays, 𝜓(3686)→𝛾𝜒𝑐𝐽(𝐽=0,1,2) and 𝜓(3686)→𝛾𝜒𝑐𝐽,𝜒𝑐𝐽→𝛾𝐽/𝜓(𝐽=1,2) events are utilized to study inclusive 𝜒𝑐𝐽→anything, 𝜒𝑐𝐽→hadrons, and 𝐽/𝜓→anything distributions, including distributions of the number of charged tracks, electromagnetic calorimeter showers, and 𝜋0s, and to compare them with distributions obtained from the BESIII Monte Carlo simulation. Information from each Monte Carlo simulated decay event is used to construct matrices connecting the detected distributions to the input predetection “produced” distributions. Assuming these matrices also apply to data, they are used to predict the analogous produced distributions of the decay events. Using these, the charged particle multiplicities are compared with results from MARK I. Further, comparison of the distributions of the number of photons in data with those in Monte Carlo simulation indicates that G-parity conservation should be taken into consideration in the simulation.
Using 5.9 pb−1 of e+e− annihilation data collected at center-of-mass energies from 3.640 to 3.701 GeV with the BESIII detector at the BEPCII Collider, we measure the observed cross sections of e+e−→K0SX (where X=anything). From a fit to these observed cross sections with the sum of continuum and ψ(3686) and J/ψ Breit-Wigner functions and considering initial state radiation and the BEPCII beam energy spread, we obtain for the first time the inclusive decay branching fraction B(ψ(3686)→K0SX)=(16.04±0.29±0.90)%, where the first uncertainty is statistical and the second is systematic.
Based on 586 pb−1 of e+e− annihilation data collected at a center-of-mass energy of s√=4.6 GeV with the BESIII detector at the BEPCII collider, the absolute branching fraction of Λ+c→pK0Sη decays is measured for the first time to be B(Λ+c→pK0Sη)=(0.414±0.084±0.028)%, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction B(Λ+c→pK0Sη)B(Λ+c→pK−π+), and consistent with theoretical predictions of SU(3) flavor symmetry.
The Born cross sections of the e+e− → +¯ − and e+e− → −¯ + processes are determined for centerof-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be described properly by a pQCD function and the resulting ratio of effective form factors for the + and − is consistent with 3. In addition, ratios of the + electric and magnetic form factors, |GE /GM |, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the ± form factors require more theoretical discussions for the hyperons.
Born cross sections for the processes e+e− → ωη and e+e− → ωπ0 have been determined for centerof-mass energies between 2.00 and 3.08 GeV with the BESIII detector at the BEPCII collider. The results obtained in this work are consistent with previous measurements but with improved precision. Two resonant structures are observed. In the e+e− → ωη cross sections, a resonance with a mass of (2176 ± 24 ± 3) MeV/c2 and a width of (89 ± 50 ± 5) MeV is observed with a significance of 6.2σ. Its properties are consistent with the φ(2170). In the e+e− → ωπ0 cross sections, a resonance denoted Y (2040) is observed with a significance of more than 10σ. Its mass and width are determined to be (2034 ± 13 ± 9) MeV/c2 and (234 ± 30 ± 25) MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.
There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like XYZ states at BESIII and B factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons.
We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII during the remaining operation period of BEPCII. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.
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−.
Relative fractions and phases of the intermediate decays are determined. With the detection efficiency estimated by the results of the amplitude analysis, the branching fraction of Dþ s → K−Kþπþπ0 decay is measured to be ð5.42 0.10stat 0.17systÞ%.
Using 𝑒+𝑒−→Λ+𝑐¯Λ−𝑐 production from a 567 pb−1 data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried out simultaneously on the four decay modes of Λ+𝑐→𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0, and Σ0𝜋+. For the first time, the Λ+𝑐 transverse polarization is studied in unpolarized 𝑒+𝑒− collisions, where a nonzero effect is observed with a statistical significance of 2.1𝜎. The decay asymmetry parameters of the Λ+𝑐 weak hadronic decays into 𝑝𝐾0𝑆, Λ𝜋+, Σ+𝜋0 and Σ0𝜋+ are measured to be 0.18±0.43(stat)±0.14(syst), −0.80±0.11(stat)±0.02(syst), −0.57±0.10(stat)±0.07(syst), and −0.73±0.17(stat)±0.07(syst), respectively. In comparison with previous results, the measurements for the Λ𝜋+ and Σ+𝜋0 modes are consistent but with improved precision, while the parameters for the 𝑝𝐾0𝑆 and Σ0𝜋+ modes are measured for the first time.
Search for the reaction channel e⁺e⁻ → ηcηπ⁺π⁻ at center-of-mass energies from 4.23 to 4.60 GeV
(2021)
Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process 𝑒+𝑒−→𝜂𝑐𝜂𝜋+𝜋−. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The 𝜂𝑐 meson is reconstructed in 16 exclusive decay modes. No signal is observed in the 𝜂𝑐 mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.
A partial-wave analysis of the decay 𝐽/𝜓→𝐾+𝐾−𝜋0 has been made using (223.7±1.4)×106 𝐽/𝜓 events collected with the BESIII detector in 2009. The analysis, which is performed within the isobar-model approach, reveals contributions from 𝐾*2(1430)±, 𝐾*2(1980)± and 𝐾*4(2045)± decaying to 𝐾±𝜋0. The two latter states are observed in 𝐽/𝜓 decays for the first time. Two resonance signals decaying to 𝐾+𝐾− are also observed. These contributions cannot be reliably identified and their possible interpretations are discussed. The measured branching fraction 𝐵(𝐽/𝜓→𝐾+𝐾−𝜋0) of (2.88±0.01±0.12)×10−3 is more precise than previous results. Branching fractions for the reported contributions are presented as well. The results of the partial-wave analysis differ significantly from those previously obtained by BESII and BABAR.
Measurement of branching fractions for D meson decaying into ϕ meson and a pseudoscalar meson
(2019)
The four decay modes D0 → φπ0, D0 → φη, D+ → φπ+, and D+ → φK + are studied by using a data sample taken at the centre-of-mass energy √s = 3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of 2.93 fb−1. The branching fractions of the first three decay modes are measured to be B(D0 → φπ0) = (1.168 ± 0.028 ± 0.028) × 10−3, B(D0 → φη) = (1.81 ± 0.46 ± 0.06) × 10−4, and B(D+ → φπ+) = (5.70 ± 0.05 ± 0.13) × 10−3, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the upper limit of the branching fraction for D+ → φK+ is given to be 2.1 × 10−5 at the 90% confidence level. The ratio of B(D0 → φπ0) to B(D+ → φπ+) is calculated to be (20.49 ± 0.50 ± 0.45)%, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes.