Measurement of the cross sections for e+e- →ηπ+π- at center-of-mass energies between 2.00 and 3.08 GeV

Using data samples collected at center-of-mass energies between 2.000 and 3.080 GeV with the BESIII detector operating at the BEPCII collider, a partial-wave analysis is performed on the process e+e-→ηπ+π-. In addition to the dominant e+e-→ρη component, the e+e-→a2(1320)π process is also sizable, contributing up to 24% of the total reaction. The measured cross sections of the process e+e-→ηπ+π- are systematically higher than those of BABAR by more than 3σ at center-of-mass energies between 2.000 and 2.300 GeV. In the cross section line shape for e+e-→a2(1320)π, a resonant structure is observed with a significance of 5.5σ, with M=(2044±31±4) MeV/c2, Γ=(163±69±24) MeV, and BR·Γe+e-R=(34.6±17.1±6.0) eV or (137.1±73.3±2.1) eV. In the cross section line shape for e+e-→ρη, an evidence of a dip structure around 2180 MeV/c2 is observed with statistical significance of 3.0σ.