Observation of Three Resonant Structures in the Cross Section of e+e- →π+π-hc

Using e+e- collision data collected with the BESIII detector operating at the Beijing electron positron collider, the cross section of e+e-→π+π-hc is measured at 59 points with center-of-mass energy s ranging from 4.009 to 4.950 GeV with a total integrated luminosity of 22.2 fb-1. The cross section between 4.3 and 4.45 GeV exhibits a plateaulike shape and drops sharply around 4.5 GeV, which cannot be described by two resonances only. Three coherent Breit-Wigner functions are used to parametrize the s-dependent cross section line shape. The masses and widths are determined to be M1=(4223.6-3.7-2.9+3.6+2.6) MeV/c2, Γ1=(58.5-11.4-6.5+10.8+6.7) MeV, M2=(4327.4-18.8-9.3+20.1+10.7) MeV/c2, Γ2=(244.1-27.1-18.3+34.0+24.2) MeV, and M3=(4467.4-5.4-2.7+7.2+3.2) MeV/c2, and Γ3=(62.8-14.4-7.0+19.2+9.9) MeV. The first uncertainties are statistical and the second are systematic. The inclusion of the relatively narrower third component proves crucial for reproducing the drop at around 4.5 GeV. The statistical significance of the three-resonance assumption over the two-resonance assumption is greater than 5σ.