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Institute
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.
The Born cross sections and effective form factors for process 𝑒+𝑒−→Ξ−¯Ξ+ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb−1 𝑒+𝑒− collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross section of 𝑒+𝑒−→Ξ−¯Ξ+, no significant threshold effect is observed.
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.
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.
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.
An amplitude analysis of the 𝐾𝑆𝐾𝑆 system produced in radiative 𝐽/𝜓 decays is performed using the (1310.6±7.0)×106 𝐽/𝜓 decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parametrizing the 𝐾𝑆𝐾𝑆 invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the 𝐾𝑆𝐾𝑆 system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the 𝑓0(1710), 𝑓0(2200), and 𝑓′2(1525). The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative 𝐽/𝜓 decays to 𝐾𝑆𝐾𝑆 is measured to be (8.1±0.4)×10−4, where the uncertainty is systematic and the statistical uncertainty is negligible.
By analyzing 2.93 fb−1 of data taken at the ψ(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ → K0S K0S K +, D+ → K0S K0Sπ+, D0 → K0S K0S and D0 → K0S K0S K0S . They are determined to be B(D+ → K0S K0S K +) = (2.54 ± 0.05stat. ± 0.12sys.) × 10−3, B(D+ → K0S K0Sπ+) = (2.70 ± 0.05stat. ± 0.12sys.) × 10−3, B(D0 → K0S K0S ) = (1.67 ± 0.11stat. ± 0.11sys.) × 10−4 and B(D0 → K0S K0S K0S ) = (7.21 ± 0.33stat. ± 0.44sys.) × 10−4, where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.
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.
Based on an 𝑒+𝑒− collision data sample corresponding to an integrated luminosity of 567 pb−1 taken at the center-of-mass energy of √𝑠=4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive decay Λ+𝑐→Λ+𝑋 to be ℬ(Λ+𝑐→Λ+𝑋)=(38.2+2.8−2.2±0.9)% using the double-tag method, where 𝑋 refers to any possible final state particles. In addition, we search for direct 𝐶𝑃 violation in the charge asymmetry of this inclusive decay for the first time, and obtain 𝒜𝐶𝑃≡[ℬ(Λ+𝑐→Λ+𝑋)−ℬ(¯Λ−𝑐 → ¯Λ+𝑋)]/[ℬ(Λ+𝑐→Λ+𝑋)+ℬ(¯Λ−𝑐 → ¯Λ+𝑋)]=(2.1+7.0−6.6±1.6)%, a statistically limited result with no evidence of 𝐶𝑃 violation.
Using 16 energy points of e+e− annihilation data collected in the vicinity of the J/ψ resonance with the BESIII detector and with a total integrated luminosity of around 100 pb−1, we study the relative phase between the strong and electromagnetic amplitudes of J/ψ decays. The relative phase between J/ψ electromagnetic decay and the continuum process (e+e− annihilation without the J/ψ resonance) is confirmed to be zero by studying the cross section lineshape of μ+μ− production. The relative phase between J/ψ strong and electromagnetic decays is then measured to be (84.9 ± 3.6)◦ or (−84.7 ± 3.1)◦ for the 2(π+π−)π0 final state by investigating the interference pattern between the J/ψ decay and the continuum process. This is the first measurement of the relative phase between J/ψ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state ηπ+π− with η → π+π−π0, which provides additional information about the phase between the J/ψ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/ψ → 2(π+π−)π0 is measured to be (4.73 ± 0.44)% or (4.85 ± 0.45)%, and the branching fraction of J/ψ → ηπ+π− is measured to be (3.78 ± 0.68) × 10−4. Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.