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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.).
Search for hidden-charm tetraquark with strangeness in eβΊeβ» β KβΊD*β»β D*β° + c.c.
(2023)
We report a search for a heavier partner of the recently observed Zcs(3985)β state, denoted as Zβ²βcs, in the process e+eββK+DββsDβ0+c.c., based on e+eβ collision data collected at the center-of-mass energies of sβ=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Zβ²βcs is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate K+ recoil-mass spectra, which are probed for a potential contribution from Zβ²βcsβDββsDβ0 (c.c.). We find an excess of Zβ²βcsβDββsDβ0 (c.c.) candidates with a significance of 2.1Ο, after considering systematic uncertainties, at a mass of (4123.5Β±0.7stat.Β±4.7syst.) MeV/c2. As the data set is limited in size, the upper limits are evaluated at the 90\% confidence level on the product of the Born cross sections (ΟBorn) and the branching fraction (B) of Zβ²βcsβDββsDβ0, under different assumptions of the Zβ²βcs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of ΟBornβ
B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Zβ²βcs state and clarify its nature in the coming years.
Search for hidden-charm tetraquark with strangeness in eβΊeβ» β KβΊD*β»β D*β° + c.c.
(2022)
We report a search for a heavier partner of the recently observed Zcs(3985)β state, denoted as Zβ²βcs, in the process e+eββK+DββsDβ0+c.c., based on e+eβ collision data collected at the center-of-mass energies of sβ=4.661, 4.682 and 4.699 GeV with the BESIII detector. The Zβ²βcs is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate K+ recoil-mass spectra, which are probed for a potential contribution from Zβ²βcsβDββsDβ0 (c.c.). We find an excess of Zβ²βcsβDββsDβ0 (c.c.) candidates with a significance of 2.1Ο, after considering systematic uncertainties, at a mass of (4123.5Β±0.7stat.Β±4.7syst.) MeV/c2. As the data set is limited in size, the upper limits are evaluated at the 90\% confidence level on the product of the Born cross sections (ΟBorn) and the branching fraction (B) of Zβ²βcsβDββsDβ0, under different assumptions of the Zβ²βcs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of ΟBornβ
B are found to be at the level of O(1) pb at each energy. Larger data samples are needed to confirm the Zβ²βcs state and clarify its nature in the coming years.
Using a data sample of 4.481Γ108ββπβ‘(3686) events collected with the BESIII detector, we report the first observation of the four-lepton-decays π½/πβπ+β’πββ’π+β’πβ and π½/πβπ+β’πββ’π+β’πβ utilizing the process πβ‘(3686)βπ+β’πββ’π½/π. The branching fractions are determined to be [5.48Β±0.31β’(stat)Β±0.45β’(syst)]Γ10β5 and [3.53Β±0.22β’(stat)Β±0.13β’(syst)]Γ10β5, respectively. The results are consistent with theoretical predictions. No significant signal is observed for π½/πβπ+β’πββ’π+β’πβ, and an upper limit on the branching fraction is set at 1.6Γ10β6 at the 90% confidence level. A πΆβ’π asymmetry observable is constructed for the first two channels, which is measured to be (β0.012Β±0.054Β±0.010) and (0.062Β±0.059Β±0.006), respectively. No evidence for πΆβ’π violation is observed in this process.
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.