Measurement of e+e- → Λ Λ ¯ η from 3.5106 to 4.6988 GeV and study of Λ Λ ¯ mass threshold enhancement

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doi:10.1103/PhysRevD.107.112001

Using data samples with a total integrated luminosity of approximately 18 fb-1 collected by the BESIII detector operating at the Beijing Electron-Positron Collider II, the process e+e- & RARR; A over bar A & eta; is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process e+e-& RARR; A over bar A & eta; is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the AA over bar mass threshold is observed for the first time in the process. The structure can be described by an S-wave Breit-Wigner function. Neglecting contribution of excited A states and potential interferences, the mass and width are determined to be (2356 & PLUSMN; 7 & PLUSMN; 15) MeV=c2 and (304 & PLUSMN; 28 & PLUSMN; 54) MeV, respectively, where the first uncertainties are statistical and the second are systematic.