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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 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.
Using a data sample of (448.1Β±2.9)Γ106ββπβ‘(3686) decays collected at an π+β’πβ center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay πβ‘(3686)βπ+β’πββ’ππ with a significance of 7.9β’π. The branching fraction is determined to be β¬β‘(πβ‘(3686)βπ+β’πββ’ππ)=(3.77Β±0.4β’0statΒ±0.1β’8syst)Γ10β5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the πβ‘(3686) and the ππ, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ππ decays.
Using about 23ββfβ’bβ1 of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the π+β’πββπ+β’πββ’π½/π Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the πβ‘(4220) and the πβ‘(4320) states, are observed in the energy-dependent cross section with a significance larger than 10β’π. The masses and widths of the two structures are determined to be (π,Ξ)=(4221.4Β±1.5Β±2.0ββMeV/π2,41.8Β±2.9Β±2.7ββMeV) and (π,Ξ)=(4298Β±12Β±26ββMeV/π2,127Β±17Β±10ββMeV), respectively. A small enhancement around 4.5 GeV with a significance about 3β’π, compatible with the πβ‘(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 πβ‘(4320) state.
The hadronic decay ππβ‘(2β’π)β3β’(π+β’πβ) is observed with a statistical significance of 9.3 standard deviations using (448.1Β±2.9)Γ106ββπβ‘(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ππβ‘(2β’π) are (3643.4Β±2.3β(stat)Β±4.4β(syst))ββMeV/π2 and (19.8Β±3.9β(stat)Β±3.1β(syst))ββMeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction β¬β‘[πβ‘(3686)βπΎβ’ππβ‘(2β’π)]Γβ¬β‘[ππβ‘(2β’π)β3β’(π+β’πβ)] is measured to be (9.2Β±1.0β(stat)Β±1.2β(syst))Γ10β6. Using β¬β‘[πβ‘(3686)βπΎβ’ππβ‘(2β’π)]=(7.β’0+3.4β2.5)Γ10β4, we obtain β¬β‘[ππβ‘(2β’π)β3β’(π+β’πβ)]=(1.31Β±0.15β(stat)Β±0.17β(syst) (+0.64β0.47)β(extr))Γ10β2, where the third uncertainty is from β¬β‘[πβ‘(3686)βπΎβ’ππβ‘(2β’π)]. We also measure the ππβ’π½β3β’(π+β’πβ) (π½=0, 1, 2) decays via πβ²βπΎβ’ππβ’π½ transitions. The branching fractions are β¬β‘[ππβ’0β3β’(π+β’πβ)]=(2.080Β±0.006β(stat)Β±0.068β(syst))Γ10β2, β¬β‘[ππβ’1β3β’(π+β’πβ)]=(1.092Β±0.004β(stat)Β±0.035β(syst))Γ10β2, and β¬β‘[ππβ’2β3β’(π+β’πβ)]=(1.565Β±0.005β(stat)Β±0.048β(syst))Γ10β2.
The hadronic decay Ξ·c(2S)β3(Ο+Οβ) is observed with a statistical significance of 9.3 standard deviations using (448.1Β±2.9)Γ106 Ο(3686) events collected by the BESIII detector at the BEPCII collider. The measured mass and width of Ξ·c(2S) are (3643.4Β±2.3(stat.)Β±4.4(syst.)) MeV/c2 and (19.8Β±3.9(stat.)Β±3.1(syst.)) MeV, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction B[Ο(3686) β Ξ³Ξ·c(2S)]ΓB[Ξ·c(2S)β3(Ο+Οβ)] is measured to be (9.2Β±1.0(stat.)Β±0.9(syst.))Γ10β6. Using B[Ο(3686)βΞ³Ξ·c(2S)]=(7.0+3.4β2.5)Γ10β4, we obtain B[Ξ·c(2S)β3(Ο+Οβ)]=(1.31Β±0.15(stat.)Β±0.13(syst.)(+0.64β0.47)(extr))Γ10β2, where the third uncertainty is from B[Ο(3686)βΞ³Ξ·c(2S)]. We also measure the ΟcJβ3(Ο+Οβ) (J=0,1,2) decays via Ο(3686)βΞ³ΟcJ transitions. The branching fractions are B[Οc0β3(Ο+Οβ)]=(2.080Β±0.006(stat.)Β±0.068(syst.))Γ10β2, B[Οc1β3(Ο+Οβ)]=(1.092Β±0.004(stat.)Β±0.035(syst.))Γ10β2, and B[Οc2β3(Ο+Οβ)]=(1.565Β±0.005(stat.)Β±0.048(syst.))Γ10β2.