Measurement of the branching fraction of ψ (2S) →γπ0

Based on (2712.4±14.1)×106 ψ(2S) events, 7.9 fb-1 ψ(3773) data, and 0.8 fb-1 off-resonance data samples collected with the BESIII detector, we measure the branching fraction of ψ(2S)→γπ0 and e+e-→γπ0 form factor at momentum transfers Q2∼13 GeV2. The e+e-→γπ0 cross section is fitted with considering the interference between the ψ(2S) and continuum amplitudes and two solutions are found, B=3.74×10-7 with φ=3.93 rad and B=7.87×10-7 with φ=2.08 rad. Here, B is the branching fraction of ψ(2S)→γπ0 and φ is the relative phase angle between the ψ(2S) and continuum amplitudes. Due to insufficient off-resonance data, the branching fraction B(ψ(2S)→γπ0) is determined to be in the range [2.7,9.7]×10-7 within 1 standard deviation of the contour region.