Measurement of e+e- to pi+pi-J/psi Cross Section via Initial State Radiation at Belle
Abstract
The cross section for e+e- to pi+pi-J/psi between 3.8 and 5.5 GeV/c2 is measured using a 548 fb-1 data sample collected on or near the Upsilon(4S) resonance with the Belle detector at KEKB. A peak near 4.25 GeV/c2, corresponding to the so called Y(4260), is observed. In addition, there is another cluster of events at around 4.05 GeV/c2. A fit using two interfering Breit-Wigner shapes describes the data better than one that uses only the Y(4260), especially for the lower mass side of the 4.25 GeV enhancement.
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