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Institute
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.
Using a sample of (448.1Β±2.9)Γ106βπβ‘(3686) decays collected with the BESIII detector at BEPCII, we report an observation of Ξβ transverse polarization with a significance of 7.3β’π in the decay πβ‘(3686)βΞββ’ Β―Ξ+ (ΞββΞβ’πβ, Β―Ξ+βΒ―Ξβ’π+, Ξβπβ’πβ, Β―ΞβΒ―πβ’π+). The relative phase of the electric and magnetic form factors is determined to be Ξβ’Ξ¦=(0.667Β±0.111Β±0.058)ββrad. This is the first measurement of the relative phase for a πβ‘(3686) decay into a pair of Ξββ’Β―Ξ+ hyperons. The Ξβ decay parameters (πΌΞβ, πΞβ) and their conjugates (πΌΒ―Ξ+, πΒ―Ξ+), the angular-distribution parameter πΌπ, and the strong-phase difference πΏπβπΏπ for Ξβ’πβ scattering are measured to be consistent with previous BESIII results.
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.).
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)βΞ³Ξ·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.
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 2.9Ο, after considering systematic uncertainties, at a mass of (4123.5Β±0.7stat.Β±1.1syst.)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 section and the branching fraction of Zβ²βcsβDββsDβ0, ΟBornβ
B at the three energy points, under different assumptions of the Zβ²βcs mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV. Under various mass and width assumptions, the upper limits of ΟBornβ
B are found to lie in the range of 2βΌ6, 3βΌ7 and 3βΌ6 pb at sβ=4.661, 4.682 and 4.699 GeV, respectively. The larger data samples that will be collected in the coming years will allow a clearer picture to emerge concerning the existence and nature of the Zβ²βcs state.
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 data samples with an integrated luminosity of 19 fbβ1 at twenty-eight center-of-mass energies from 3.872 GeV to 4.700 GeV collected with the BESIII detector at the BEPCII electron-positron collider, the process e+eβ β Ξ·Ο+Οβ and the intermediate process e+eβ β Ξ·Ο0 are studied for the first time. The Born cross sections are measured. No significant resonance structure is observed in the cross section lineshape.
Using a sample of about 1010ββπ½/π events collected at a center-of-mass energy βπ =3.097ββGeV with the BESIII detector, the electromagnetic Dalitz decays π½/πβπ+β’πββ’π+β’πββ’πβ², with πβ²βπΎβ’π+β’πβ and πβ²βπ+β’πββ’π, have been studied. The decay π½/πβπ+β’πββ’πβ‘(1835) is observed with a significance of 15β’π, and also an π+β’πβ invariant-mass dependent transition form factor of π½/πβπ+β’πββ’πβ‘(1835) is presented for the first time. The intermediate states πβ‘(2120) and πβ‘(2370) are also observed in the π+β’πββ’πβ² invariant-mass spectrum with significances of 5.3β’π and 7.3β’π. The corresponding product branching fractions for π½/πβπ+β’πββ’π, πβπ+β’πββ’πβ² [π=πβ‘(1835), πβ‘(2120), and πβ‘(2370)] are reported.
Based on (10087Β±44)Γ106ββπ½/π events collected with the BESIII detector at BEPCII, the double Dalitz decay πβ²βπ+β’πββ’π+β’πβ is observed for the first time via the π½/πβπΎβ’πβ² decay process. The significance is found to be 5.7β’π with systematic uncertainties taken into consideration. Its branching fraction is determined to be β¬β‘(πβ²βπ+β’πββ’π+β’πβ)=(4.5Β±1.0β’(stat)Β±0.5β’(sys))Γ10β6.