Precision measurement of the branching fractions of η′ decays

Based on a sample of (1310.6±7.0)×106J/ψ events collected with the BESIII detector, we present measurements of J/ψ and η′ absolute branching fractions using the process J/ψ→γη′. By analyzing events where the radiative photon converts into an e+e-pair, the branching fraction for J/ψ→γη′ is measured to be (5.27±0.03±0.05)×10-3. The absolute branching fractions of the five dominant decay channels of the η′ are then measured for the first time and are determined to be B(η′→γπ+π-)=(29.90±0.03±0.55)%, B(η′→ηπ+π-)=(41.24±0.08±1.24)%, B(η′→ηπ0π0)=(21.36±0.10±0.92)%, B(η′→γω)=(2.489±0.018±0.074)%, and B(η′→γγ)=(2.331±0.012±0.035)%, where the first uncertainties are statistical and the second systematic.