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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.
The integrated luminosities of data samples collected in the BESIII experiment in 2016β2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010β2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur.
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 β¬(J/ΟβββDβe+Ξ½eβ+βc. c.)β<β7.1βΓβ10β8 is obtained at 90% confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.
Based on an e+eβ collision data sample corresponding to an integrated luminosity of 2.93 fbβ1 collected with the BESIII detector at βs=3.773 GeV, the first amplitude analysis of the singly Cabibbo-suppressed decay D+βK+K0SΟ0 is performed. From the amplitude analysis, the Kβ(892)+K0S component is found to be dominant with a fraction of (57.1Β±2.6Β±4.2)%, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction B(D+βK+K0SΟ0) measured by BESIII, we obtain B(D+βKβ(892)+K0S)=(8.69Β±0.40Β±0.64Β±0.51)Γ10β3, where the third uncertainty is due to the branching fraction B(D+βK+K0SΟ0). The precision of this result is significantly improved compared to the previous measurement. This result also differs from most of theoretical predictions by about 4Ο, which may help to improve the understanding of the dynamics behind.
Using a data sample of (1310.6Β±7.0)Γ106ββπ½/π events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay Ξ£ββπβ’πββ’πβ and the rare inclusive decay Ξ£ββΞ£+β’π, where π denotes any possible particle combination. The Ξ£β candidates are tagged in π½/πβΒ―Ξ£β’(1385)+β’Ξ£β decays. No signal candidates are found, and the upper limits on the branching fractions at the 90% confidence level are determined to be β¬β‘(Ξ£ββπβ’πββ’πβ)<6.7Γ10β5 and β¬β‘(Ξ£ββΞ£+β’π)<1.2Γ10β4.
The integrated luminosities of the data samples collected in the BESIII experiment in 2016--2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% by analyzing large-angle Bhabha scattering events. The integrated luminosities of the old data sets collected in 2010--2014 are updated by considering correction related to the detector performance, offsettting the effect of newly discovered readout errors in the electromagnetic calorimeter that happen haphazardly.
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 2.93 fbβ1 of e+eβ collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0βK1(1270)βe+Ξ½e semileptonic decay is presented. The statistical significance of the decay D0βK1(1270)βe+Ξ½e is greater than 10Ο. The branching fraction of D0βK1(1270)βe+Ξ½e is measured to be (1.09Β±0.13+0.09β0.13Β±0.12)Γ10β3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)ββKβΟ+Οβ.
Using 2.93 fbβ1 of e+eβ collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D0βK1(1270)βe+Ξ½e semileptonic decay is presented. The statistical significance of the decay D0βK1(1270)βe+Ξ½e is greater than 10Ο. The branching fraction of D0βK1(1270)βe+Ξ½e is measured to be (1.09Β±0.13+0.09β0.16Β±0.12)Γ10β3. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K1(1270)ββKβΟ+Οβ. The fraction of longitudinal polarization in D0βK1(1270)βe+Ξ½e is determined for the first time to be 0.50Β±0.19statΒ±0.08syst.
The process e+eββΟΞ· is studied at 22 center-of-mass energy points (βs) between 2.00 and 3.08 GeV using 715ββpbβ1 of data collected with the BESIII detector. The measured Born cross section of e+eββΟΞ· is found to be consistent with BABAR measurements, but with improved precision. A resonant structure around 2.175 GeV is observed with a significance of 6.9Ο with mass (2163.5Β±6.2Β±3.0)ββMeV/c2 and width (31.1+21.1β11.6Β±1.1)ββMeV, where the first uncertainties are statistical and the second are systematic.
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.
Measurement of the branching fraction of leptonic decay D+s β Ο+Ξ½Ο via Ο+ β Ο+Ο0Β―Ξ½Ο
(2021)
By analyzing 6.32 fb β 1 of e+ eβ annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay D + s β Ο + Ξ½Ο, with Ο+ β Ο + Ο0Β―Ξ½Ο, to be B D + s β Ο + Ξ½ Ο = (5.29 Β± 0.25 stat Β± 0.20 syst) %. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element |Vcs|and the D + s decay constant f D + s to be f D + s|Vcs| = (244.8 Β± 5.8 stat Β± 4.8syst) MeV, using the known values of the Ο + and D + s masses as well as the D + s lifetime, together with our branching fraction measurement. Combining the value of |Vcs| obtained from a global fit in the standard model and f D + s from lattice quantum chromodynamics, we obtain f D + s = (251.6 Β± 5.9 stat Β± 4.9syst) MeV and |Vcs| = 0.980 Β± 0.023 stat Β± 0.019 syst. Using the branching fraction of B D + s β ΞΌ + Ξ½ΞΌ = (5.35Β±0.21)Γ10β3, we obtain the ratio of the branching fractions B D + s β Ο + Ξ½Ο/B D +s β ΞΌ+Ξ½ΞΌ = 9.89Β±0.71, which is consistent with the standard model prediction of lepton flavor universality.
Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process eΓΎeβ β Ο0XΓ°3872ΓΞ³ and search for ZcΓ°4020Γ0 β XΓ°3872ΓΞ³. We find no significant signal and set upper limits on ΟΓ°eΓΎeβ β Ο0XΓ°3872ΓΞ³Γ Β· BΓ°XΓ°3872Γ β ΟΓΎΟβJ=ΟΓ and ΟΓ°eΓΎeβ β Ο0ZcΓ°4020Γ0Γ Β· BΓ°ZcΓ°4020Γ0 β XΓ°3872ΓΞ³Γ Β· BΓ°XΓ°3872Γ β ΟΓΎΟβJ=ΟΓ for each energy point at 90% confidence level, which is of the order of several tenths pb.
We measure the inclusive semielectronic decay branching fraction of the D+s meson. A double-tag technique is applied to e+eβ annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range 4.178β4.230 GeV. We select positrons fromD+sβXe+Ξ½e with momenta greater than 200 MeV/c and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the D+s semielectronic branching fraction to be(6.30Β±0.13(stat.)Β±0.09(syst.)Β±0.04(ext.))%, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the D+s and D0 semielectronic widths, Ξ(D+sβXe+Ξ½e)Ξ(D0βXe+Ξ½e)=0.790Β±0.016(stat.)Β±0.011(syst.)Β±0.016(ext.). Our results are consistent with and more precise than previous measurements.
The electromagnetic process is studied with the initial-state-radiation technique using 7.5 fbβ1 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.
Using a data sample corresponding to an integrated luminosity of 2.93ββfbβ1 collected at a center-of-mass energy βπ =3.773ββGeV by the BESIII detector, the decay π·0βπβ’π is observed for the first time. The branching fraction is measured to be (6.48Β±0.96Β±0.40)Γ10β4 with a significance of 6.3β’π, where the first and second uncertainties are statistical and systematic, respectively. An angular analysis reveals that the π and π mesons from the π·0βπβ’π decay are transversely polarized. The 95% confidence level upper limit on longitudinal polarization fraction is set to be less than 0.24, which is inconsistent with current theoretical expectations and challenges our understanding of the underlying dynamics in charm meson decays.
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.
Using a total of 5.25 fbβ1 of e+eβ collision data with center-of-mass energies from 4.236 to 4.600 GeV, we report the first observation of the process e+eβ β Ξ·Ο(2S) with a statistical significance of 4.9 standard deviations. The data sets were collected by the BESIII detector operating at the BEPCII storage ring. We measure the yield of events integrated over center-of-mass energies and also present the energy dependence of the measured cross section.
The decays D β KβΟ+Ο+Οβ and D β KβΟ+Ο 0 are studied in a sample of quantum-correlated DDΒ― pairs produced through the process e+eβ β Ο(3770) β DDΒ―, exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fbβ1 . Here D indicates a quantum superposition of a D0 and a DΒ― 0 meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle Ξ³ of the Unitarity Triangle in Bβ β DKβ decays at the LHCb and Belle II experiments. The coherence factors are determined to be RK3Ο = 0.52+0.12β0.10 and RKΟΟ0 = 0.78 Β± 0.04, with values for the average strong-phase differences that are Ξ΄ K3Ο D = (167+31β19)β¦ and Ξ΄KΟΟ0D = (196+14β15β¦ , where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the D β KβΟ+Ο+Οβ to yield results that will allow for a more sensitive measurement of Ξ³ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6β¦.
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.