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By using 6.32 fbβ1 of data collected with the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, we perform an amplitude analysis of the decay D+s ! K0S +β0 and determine the relative fractions and phase differences of different intermediate processes, which include K0S (770)+, K0S (1450)+, Kβ(892)0β+, Kβ(892)+β0, and Kβ(1410)0β+. With the detection efficiency based on the amplitude analysis results, the absolute branching fraction is measured to be B(D+s ! K0S +β0) = (5.43 Β± 0.30stat Β± 0.15syst) Γ 10β3.
Using a data sample of 448.1 Γ 106 Ο(3686) events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay Ο(3686) β Ξ· e+eβ, with significances of 7.0Ο and 6.3Ο when reconstructing the Ξ· meson via its decay modes Ξ· β Ξ³Ο+Οβ and Ξ· β Ο+ΟβΞ· (Ξ· β Ξ³Ξ³ ), respectively. The weighted average branching fraction is determined to be B(Ο(3686) β Ξ· e+eβ) = (1.90 Β± 0.25 Β± 0.11) Γ 10β6, where the first uncertainty is statistical and the second systematic.
Using e+eβ annihilation data sets collected with the BESIII detector, we measure the cross sections of the processes e+eββe+eβ and e+eββΞΌ+ΞΌβ at fifteen center-of-mass energy points in the vicinity of the J/Ο resonance. By a simultaneous fit to the measured, center-of-mass energy dependent cross sections of the two processes, the combined quantities ΞeeΞee/Ξtot and ΞeeΞΞΌΞΌ/Ξtot are determined to be (0.346Β±0.009) and (0.335Β±0.006) keV, respectively, where Ξee, ΞΞΌΞΌ, and Ξtot are the electronic, muonic, and total decay widths of the J/Ο resonance, respectively. Using the resultant ΞeeΞΞΌΞΌ/Ξtot and ΞeeΞee/Ξtot, the ratio Ξee/ΞΞΌΞΌ is calculated to be 1.031Β±0.015, which is consistent with the expectation of lepton universality within about two standard deviations. Assuming lepton universality and using the branching fraction of the J/Ο leptonic decay measured by BESIII in 2013, Ξtot and Ξll are determined to be (93.0Β±2.1) and (5.56Β±0.11) keV, respectively, where Ξll is the average leptonic decay width of the J/Ο resonance.
By analyzing (448.1Β±2.9)Γ106ββπβ‘(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of ππβ’π½βΞβ’
Β―Ξβ’π (π½=0, 1, and 2) are observed for the first time with statistical significances of 13.9β’π, 6.7β’π, and 8.2β’π, respectively. The product branching fractions of πβ‘(3686)βπΎβ’ππβ’π½ and ππβ’π½βΞβ’Β―Ξβ’π are measured. Dividing by the world averages of the branching fractions of πβ‘(3686)βπΎβ’ππβ’π½, the branching fractions of ππβ’π½βΞβ’Β―Ξβ’π decays are determined to be (2.31Β±0.30Β±0.21)Γ10β4, (5.86Β±1.38Β±0.68)Γ10β5, and (1.05Β±0.21Β±0.15)Γ10β4 for π½=0, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.
The radiative hyperon decay ΞβnΞ³ is studied using (10087Β±44)Γ106 J/Ο events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay ΞβnΞ³ is determined with a significance of 5.6Ο to be [0.832Β±0.038(stat.)Β±0.054(syst.)]Γ10β3, which lies significantly below the current PDG value. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry Ξ±Ξ³ is reported with a value of β0.16Β±0.10(stat.)Β±0.05(syst.).
Using inclusive decays of the J/Ο, a precise determination of the number of J/Ο events collected with the BESIII detector is performed. For the two data sets taken in 2009 and 2012, the numbers of J/Ο events are recalculated to be (224.0Β±1.3)Γ106 and (1088.5Β±4.4)Γ106 respectively, which are in good agreement with the previous measurements. For the J/Ο sample taken in 2017--2019, the number of events is determined to be (8774.0Β±39.4)Γ106. The total number of J/Ο events collected with the BESIII detector is determined to be (10087Β±44)Γ106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
Using inclusive decays of the J/Ο, a precise determination of the number of J/Ο events collected with the BESIII detector is performed. For the two data sets taken in 2009 and 2012, the numbers of J/Ο events are recalculated to be (224.0Β±1.3)Γ106 and (1088.5Β±4.4)Γ106 respectively, which are in good agreement with the previous measurements. For the J/Ο sample taken in 2017--2019, the number of events is determined to be (8774.0Β±39.4)Γ106. The total number of J/Ο events collected with the BESIII detector is determined to be (10087Β±44)Γ106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
Using about 23 fbβ1 of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the e+eββΟ+ΟβJ/Ο Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the Y(4220) and the Y(4320) states, are observed in the energy-dependent cross section with a significance larger than 10Ο. The masses and widths of the two structures are determined to be (M,Ξ) = (4221.4Β±1.5Β±2.0 MeV/c2, 41.8Β±2.9Β±2.7 MeV) and (M,Ξ) = (4298Β±12Β±26 MeV/c2, 127Β±17Β±10 MeV), respectively. A small enhancement around 4.5 GeV with a significance about 3Ο, compatible with the Ο(4415), might also indicate the presence of an additional resonance in the spectrum. The inclusion of this additional contribution in the fit to the cross section affects the resonance parameters of the Y(4320) state.
Using about 23 fbβ1 of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the e+eββΟ+ΟβJ/Ο Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the Y(4220) and the Y(4320) states, are observed in the energy-dependent cross section with a significance larger than 10Ο. The masses and widths of the two structures are determined to be (M,Ξ) = (4221.4Β±1.5Β±2.0 MeV/c2, 41.8Β±2.9Β±2.7 MeV) and (M,Ξ) = (4298Β±12Β±26 MeV/c2, 127Β±17Β±10 MeV), respectively. A small enhancement around 4.5 GeV with a significance about 3Ο, compatible with the Ο(4415), might also indicate the presence of an additional resonance in the spectrum. The inclusion of this additional contribution in the fit to the cross section affects the resonance parameters of the Y(4320) state.
By analyzing an electron-positron collision data sample corresponding to an integrated luminosity of 2.93ββfbβ1 taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, we obtain for the first time the absolute branching fractions for seven π·0 and π·+ hadronic decay modes and search for the hadronic decay π·0βπΎ0πβ’πΎ0πβ’π0 with much improved sensitivity. The results are β¬β‘(π·0βπΎ0πβ’π0β’π0β’π0)=(7.64Β±0.30Β±0.29)Γ10β3, β‘(π·0βπΎββ’π+β’π0β’π0β’π0)=9.54Β±0.30Β±0.31)Γ10β3, β¬β‘(π·0βπΎ0πβ’π+β’πββ’π0β’π0)=(12.66Β±0.45Β±0.43)Γ10β3, β¬β‘(π·+βπΎ0πβ’π+β’π0β’π0)=(29.04Β±0.62Β±0.87)Γ10β3, β¬β‘(π·+βπΎ0πβ’π+β’π+β’πββ’π0)=(15.28Β±0.57Β±0.60)Γ10β3, β¬β‘(π·+βπΎ0πβ’π+β’π0β’π0β’π0)=(5.54Β±0.44Β±0.32)Γ10β3, β¬β‘(π·+βπΎββ’π+β’π+β’π0β’π0)=(4.95Β±0.26Β±0.19)Γ10β3, and β¬β‘(π·0βπΎ0πβ’πΎ0πβ’π0)<1.45Γ10β4 at the 90% confidence level. Here, the first uncertainties are statistical, and the second ones are systematic. The newly studied decays greatly enrich the knowledge of the π·βΒ―πΎβ’πβ’πβ’π and π·βΒ―πΎβ’πβ’πβ’πβ’π hadronic decays and open a bridge to access more two-body hadronic π· decays containing scalar, vector, axial, and tensor mesons in the charm sector.