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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 10.1 Γ 109 J/Ο events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy βs = 3.097 GeV and collected with the BESIII detector, we present a search for the rare semi-leptonic decay J/Ο β Dβe+Ξ½e + c.c. No excess of signal above background is observed, and an upper limit on the branching fraction B(J/Ο β Dβe +Ξ½e + c.c.) < 7.1 Γ 10β8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.
Using a sample of (10.09Β±0.04)Γ109 J/Ο events collected with the BESIII detector, a partial wave analysis of J/ΟβΞ³Ξ·β²Ξ·β² is performed.The masses and widths of the observed resonances and their branching fractions are reported. The main contribution is from J/ΟβΞ³f0(2020) with f0(2020)βΞ·β²Ξ·β², which is found with a significance of greater than 25Ο. The product branching fraction B(J/Ο β Ξ³f0(2020))β
B(f0(2020) β Ξ·β²Ξ·β² is measured to be (2.63Β±0.06(stat.) + 0.31β0.46(syst.))Γ10β4.
Using (10.087Β±0.044)Γ109ββπ½/π events collected by the Beijing Spectrum III (BESIII) detector at the Beijing Electron Positron Collider II (BEPCII) collider, we search for the hyperon semileptonic decay ΞββΞ0β’πββ’Β―ππ. No significant signal is observed and the upper limit on the branching fraction β¬β‘(ΞββΞ0β’πββ’Β―ππ) is set to be 2.59Γ10β4 at 90% confidence level. This result is one order of magnitude more strict than the previous best limit.
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.
Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matterβantimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry1. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryonβantibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξβ baryon and its antiparticle2 ΞΒ―+
, has enabled a direct determination of the weak-phase difference, (ΞΎPβββΞΎS)β= (1.2βΒ±β3.4βΒ±β0.8)βΓβ10β2βrad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods3. Finally, we provide an independent measurement of the recently debated Ξ decay parameter Ξ±Ξ (refs.β4,5). The ΞΞΒ―
asymmetry is in agreement with and compatible in precision to the most precise previous measurement.
Cross section measurement of eβΊeβ» β ΟβΊΟβ»Ο(3686) from βs = 4.0076 GeV to 4.6984 GeV
(2021)
Using data samples with a total integrated luminosity of 20.1ββfbβ1 collected by the BESIII detector operating at the BEPCII collider, the cross section of the process π+β’πββπ+β’πββ’πβ‘(3686) is measured at center-of-mass energies between 4.0076 and 4.6984 GeV. The measured cross section is consistent with previous results, and with much improved precision. A fit to the measured energy-dependent cross section, which includes three Breit-Wigner functions and a nonresonant contribution, confirms the existence of the charmonium-like states πβ‘(4220), πβ‘(4390), and πβ‘(4660). This is the first observation of the πβ‘(4660) at the BESIII experiment.
We report new measurements of the branching fraction β¬β‘(π·+π ββ+β’π), where β+ is either π+ or π+β‘(βπ+β’Β―ππ), based on 6.32ββfbβ1 of electron-positron annihilation data collected by the BESIII experiment at six center-of-mass energy points between 4.178 and 4.226 GeV. Simultaneously floating the π·+π βπ+β’ππ and π·+π βπ+β’ππ components yields β¬β‘(π·+π βπ+β’ππ)=(5.21Β±0.25Β±0.17)Γ10β2, β¬β‘(π·+π βπ+β’ππ)=(5.35Β±0.13Β±0.16)Γ10β3, and the ratio of decay widths π
=Ξβ‘(π·+π βπ+β’ππ)Ξβ‘(π·+π βπ+β’ππ)=9.7β’3+0.61β0.58Β±0.36, where the first uncertainties are statistical and the second systematic. No evidence of πΆβ’π asymmetry is observed in the decay rates π·Β±π βπΒ±β’ππ and π·Β±π βπΒ±β’ππ: π΄πΆβ’πβ‘(πΒ±β’π)=(β1.2Β±2.5Β±1.0)% and π΄πΆβ’πβ‘(πΒ±β’π)=(+2.9Β±4.8Β±1.0)%. Constraining our measurement to the Standard Model expectation of lepton universality (π
=9.75), we find the more precise results β¬β‘(π·+π βπ+β’ππ)=(5.22Β±0.10Β±0.14)Γ10β2 and π΄πΆβ’πβ‘(πΒ±β’ππ)=(β0.1Β±1.9Β±1.0)%. Combining our results with inputs external to our analysis, we determine the πβΒ―π quark mixing matrix element, π·+π decay constant, and ratio of the decay constants to be |ππβ’π |=0.973Β±0.009Β±0.014, ππ·+π =249.9Β±2.4Β±3.5ββMeV, and ππ·+π /ππ·+=1.232Β±0.035, respectively.