Observation of the Φ (1680) and the Y(2175) in e+e-→Φ π+π

The cross sections for e+e-→Φ π+π- and e+e-→Φ f0(980) are measured from threshold to s=3.0GeV using initial-state radiation. The analysis is based on a data sample of 673fb-1 collected on and below the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. First measurements are reported for the resonance parameters of the Φ (1680) in the Φ π+π- mode: m=(1689±7±10)MeV/c2 and Γ=(211±14±19)MeV/c2. A structure at s=2.1GeV/c2, corresponding to the so called Y(2175), is observed; its mass and width are determined to be (2079±13-28+79)MeV/c2 and (192±23-61+25)MeV/c2, respectively. © 2009 The American Physical Society.